Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1767 insertions, 0 deletions

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
new file mode 100644
index 000000000..cf9a2fa7f
--- /dev/null
+++ b/fs/erofs/zdata.c
@@ -0,0 +1,1767 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2018 HUAWEI, Inc.
+ *             https://www.huawei.com/
+ * Copyright (C) 2022 Alibaba Cloud
+ */
+#include "compress.h"
+#include <linux/prefetch.h>
+#include <linux/psi.h>
+
+#include <trace/events/erofs.h>
+
+#define Z_EROFS_PCLUSTER_MAX_PAGES	(Z_EROFS_PCLUSTER_MAX_SIZE / PAGE_SIZE)
+#define Z_EROFS_INLINE_BVECS		2
+
+/*
+ * let's leave a type here in case of introducing
+ * another tagged pointer later.
+ */
+typedef void *z_erofs_next_pcluster_t;
+
+struct z_erofs_bvec {
+	struct page *page;
+	int offset;
+	unsigned int end;
+};
+
+#define __Z_EROFS_BVSET(name, total) \
+struct name { \
+	/* point to the next page which contains the following bvecs */ \
+	struct page *nextpage; \
+	struct z_erofs_bvec bvec[total]; \
+}
+__Z_EROFS_BVSET(z_erofs_bvset,);
+__Z_EROFS_BVSET(z_erofs_bvset_inline, Z_EROFS_INLINE_BVECS);
+
+/*
+ * Structure fields follow one of the following exclusion rules.
+ *
+ * I: Modifiable by initialization/destruction paths and read-only
+ *    for everyone else;
+ *
+ * L: Field should be protected by the pcluster lock;
+ *
+ * A: Field should be accessed / updated in atomic for parallelized code.
+ */
+struct z_erofs_pcluster {
+	struct erofs_workgroup obj;
+	struct mutex lock;
+
+	/* A: point to next chained pcluster or TAILs */
+	z_erofs_next_pcluster_t next;
+
+	/* L: the maximum decompression size of this round */
+	unsigned int length;
+
+	/* L: total number of bvecs */
+	unsigned int vcnt;
+
+	/* I: page offset of start position of decompression */
+	unsigned short pageofs_out;
+
+	/* I: page offset of inline compressed data */
+	unsigned short pageofs_in;
+
+	union {
+		/* L: inline a certain number of bvec for bootstrap */
+		struct z_erofs_bvset_inline bvset;
+
+		/* I: can be used to free the pcluster by RCU. */
+		struct rcu_head rcu;
+	};
+
+	union {
+		/* I: physical cluster size in pages */
+		unsigned short pclusterpages;
+
+		/* I: tailpacking inline compressed size */
+		unsigned short tailpacking_size;
+	};
+
+	/* I: compression algorithm format */
+	unsigned char algorithmformat;
+
+	/* L: whether partial decompression or not */
+	bool partial;
+
+	/* L: indicate several pageofs_outs or not */
+	bool multibases;
+
+	/* A: compressed bvecs (can be cached or inplaced pages) */
+	struct z_erofs_bvec compressed_bvecs[];
+};
+
+/* let's avoid the valid 32-bit kernel addresses */
+
+/* the end of a chain of pclusters */
+#define Z_EROFS_PCLUSTER_TAIL           ((void *)0x5F0ECAFE)
+#define Z_EROFS_PCLUSTER_NIL            (NULL)
+
+struct z_erofs_decompressqueue {
+	struct super_block *sb;
+	atomic_t pending_bios;
+	z_erofs_next_pcluster_t head;
+
+	union {
+		struct completion done;
+		struct work_struct work;
+	} u;
+	bool eio, sync;
+};
+
+static inline bool z_erofs_is_inline_pcluster(struct z_erofs_pcluster *pcl)
+{
+	return !pcl->obj.index;
+}
+
+static inline unsigned int z_erofs_pclusterpages(struct z_erofs_pcluster *pcl)
+{
+	if (z_erofs_is_inline_pcluster(pcl))
+		return 1;
+	return pcl->pclusterpages;
+}
+
+/*
+ * bit 30: I/O error occurred on this page
+ * bit 0 - 29: remaining parts to complete this page
+ */
+#define Z_EROFS_PAGE_EIO			(1 << 30)
+
+static inline void z_erofs_onlinepage_init(struct page *page)
+{
+	union {
+		atomic_t o;
+		unsigned long v;
+	} u = { .o = ATOMIC_INIT(1) };
+
+	set_page_private(page, u.v);
+	smp_wmb();
+	SetPagePrivate(page);
+}
+
+static inline void z_erofs_onlinepage_split(struct page *page)
+{
+	atomic_inc((atomic_t *)&page->private);
+}
+
+static inline void z_erofs_page_mark_eio(struct page *page)
+{
+	int orig;
+
+	do {
+		orig = atomic_read((atomic_t *)&page->private);
+	} while (atomic_cmpxchg((atomic_t *)&page->private, orig,
+				orig | Z_EROFS_PAGE_EIO) != orig);
+}
+
+static inline void z_erofs_onlinepage_endio(struct page *page)
+{
+	unsigned int v;
+
+	DBG_BUGON(!PagePrivate(page));
+	v = atomic_dec_return((atomic_t *)&page->private);
+	if (!(v & ~Z_EROFS_PAGE_EIO)) {
+		set_page_private(page, 0);
+		ClearPagePrivate(page);
+		if (!(v & Z_EROFS_PAGE_EIO))
+			SetPageUptodate(page);
+		unlock_page(page);
+	}
+}
+
+#define Z_EROFS_ONSTACK_PAGES		32
+
+/*
+ * since pclustersize is variable for big pcluster feature, introduce slab
+ * pools implementation for different pcluster sizes.
+ */
+struct z_erofs_pcluster_slab {
+	struct kmem_cache *slab;
+	unsigned int maxpages;
+	char name[48];
+};
+
+#define _PCLP(n) { .maxpages = n }
+
+static struct z_erofs_pcluster_slab pcluster_pool[] __read_mostly = {
+	_PCLP(1), _PCLP(4), _PCLP(16), _PCLP(64), _PCLP(128),
+	_PCLP(Z_EROFS_PCLUSTER_MAX_PAGES)
+};
+
+struct z_erofs_bvec_iter {
+	struct page *bvpage;
+	struct z_erofs_bvset *bvset;
+	unsigned int nr, cur;
+};
+
+static struct page *z_erofs_bvec_iter_end(struct z_erofs_bvec_iter *iter)
+{
+	if (iter->bvpage)
+		kunmap_local(iter->bvset);
+	return iter->bvpage;
+}
+
+static struct page *z_erofs_bvset_flip(struct z_erofs_bvec_iter *iter)
+{
+	unsigned long base = (unsigned long)((struct z_erofs_bvset *)0)->bvec;
+	/* have to access nextpage in advance, otherwise it will be unmapped */
+	struct page *nextpage = iter->bvset->nextpage;
+	struct page *oldpage;
+
+	DBG_BUGON(!nextpage);
+	oldpage = z_erofs_bvec_iter_end(iter);
+	iter->bvpage = nextpage;
+	iter->bvset = kmap_local_page(nextpage);
+	iter->nr = (PAGE_SIZE - base) / sizeof(struct z_erofs_bvec);
+	iter->cur = 0;
+	return oldpage;
+}
+
+static void z_erofs_bvec_iter_begin(struct z_erofs_bvec_iter *iter,
+				    struct z_erofs_bvset_inline *bvset,
+				    unsigned int bootstrap_nr,
+				    unsigned int cur)
+{
+	*iter = (struct z_erofs_bvec_iter) {
+		.nr = bootstrap_nr,
+		.bvset = (struct z_erofs_bvset *)bvset,
+	};
+
+	while (cur > iter->nr) {
+		cur -= iter->nr;
+		z_erofs_bvset_flip(iter);
+	}
+	iter->cur = cur;
+}
+
+static int z_erofs_bvec_enqueue(struct z_erofs_bvec_iter *iter,
+				struct z_erofs_bvec *bvec,
+				struct page **candidate_bvpage)
+{
+	if (iter->cur == iter->nr) {
+		if (!*candidate_bvpage)
+			return -EAGAIN;
+
+		DBG_BUGON(iter->bvset->nextpage);
+		iter->bvset->nextpage = *candidate_bvpage;
+		z_erofs_bvset_flip(iter);
+
+		iter->bvset->nextpage = NULL;
+		*candidate_bvpage = NULL;
+	}
+	iter->bvset->bvec[iter->cur++] = *bvec;
+	return 0;
+}
+
+static void z_erofs_bvec_dequeue(struct z_erofs_bvec_iter *iter,
+				 struct z_erofs_bvec *bvec,
+				 struct page **old_bvpage)
+{
+	if (iter->cur == iter->nr)
+		*old_bvpage = z_erofs_bvset_flip(iter);
+	else
+		*old_bvpage = NULL;
+	*bvec = iter->bvset->bvec[iter->cur++];
+}
+
+static void z_erofs_destroy_pcluster_pool(void)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(pcluster_pool); ++i) {
+		if (!pcluster_pool[i].slab)
+			continue;
+		kmem_cache_destroy(pcluster_pool[i].slab);
+		pcluster_pool[i].slab = NULL;
+	}
+}
+
+static int z_erofs_create_pcluster_pool(void)
+{
+	struct z_erofs_pcluster_slab *pcs;
+	struct z_erofs_pcluster *a;
+	unsigned int size;
+
+	for (pcs = pcluster_pool;
+	     pcs < pcluster_pool + ARRAY_SIZE(pcluster_pool); ++pcs) {
+		size = struct_size(a, compressed_bvecs, pcs->maxpages);
+
+		sprintf(pcs->name, "erofs_pcluster-%u", pcs->maxpages);
+		pcs->slab = kmem_cache_create(pcs->name, size, 0,
+					      SLAB_RECLAIM_ACCOUNT, NULL);
+		if (pcs->slab)
+			continue;
+
+		z_erofs_destroy_pcluster_pool();
+		return -ENOMEM;
+	}
+	return 0;
+}
+
+static struct z_erofs_pcluster *z_erofs_alloc_pcluster(unsigned int nrpages)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(pcluster_pool); ++i) {
+		struct z_erofs_pcluster_slab *pcs = pcluster_pool + i;
+		struct z_erofs_pcluster *pcl;
+
+		if (nrpages > pcs->maxpages)
+			continue;
+
+		pcl = kmem_cache_zalloc(pcs->slab, GFP_NOFS);
+		if (!pcl)
+			return ERR_PTR(-ENOMEM);
+		pcl->pclusterpages = nrpages;
+		return pcl;
+	}
+	return ERR_PTR(-EINVAL);
+}
+
+static void z_erofs_free_pcluster(struct z_erofs_pcluster *pcl)
+{
+	unsigned int pclusterpages = z_erofs_pclusterpages(pcl);
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(pcluster_pool); ++i) {
+		struct z_erofs_pcluster_slab *pcs = pcluster_pool + i;
+
+		if (pclusterpages > pcs->maxpages)
+			continue;
+
+		kmem_cache_free(pcs->slab, pcl);
+		return;
+	}
+	DBG_BUGON(1);
+}
+
+static struct workqueue_struct *z_erofs_workqueue __read_mostly;
+
+void z_erofs_exit_zip_subsystem(void)
+{
+	destroy_workqueue(z_erofs_workqueue);
+	z_erofs_destroy_pcluster_pool();
+}
+
+static inline int z_erofs_init_workqueue(void)
+{
+	const unsigned int onlinecpus = num_possible_cpus();
+
+	/*
+	 * no need to spawn too many threads, limiting threads could minimum
+	 * scheduling overhead, perhaps per-CPU threads should be better?
+	 */
+	z_erofs_workqueue = alloc_workqueue("erofs_unzipd",
+					    WQ_UNBOUND | WQ_HIGHPRI,
+					    onlinecpus + onlinecpus / 4);
+	return z_erofs_workqueue ? 0 : -ENOMEM;
+}
+
+int __init z_erofs_init_zip_subsystem(void)
+{
+	int err = z_erofs_create_pcluster_pool();
+
+	if (err)
+		return err;
+	err = z_erofs_init_workqueue();
+	if (err)
+		z_erofs_destroy_pcluster_pool();
+	return err;
+}
+
+enum z_erofs_pclustermode {
+	Z_EROFS_PCLUSTER_INFLIGHT,
+	/*
+	 * a weak form of Z_EROFS_PCLUSTER_FOLLOWED, the difference is that it
+	 * could be dispatched into bypass queue later due to uptodated managed
+	 * pages. All related online pages cannot be reused for inplace I/O (or
+	 * bvpage) since it can be directly decoded without I/O submission.
+	 */
+	Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE,
+	/*
+	 * The current collection has been linked with the owned chain, and
+	 * could also be linked with the remaining collections, which means
+	 * if the processing page is the tail page of the collection, thus
+	 * the current collection can safely use the whole page (since
+	 * the previous collection is under control) for in-place I/O, as
+	 * illustrated below:
+	 *  ________________________________________________________________
+	 * |  tail (partial) page |          head (partial) page           |
+	 * |  (of the current cl) |      (of the previous collection)      |
+	 * |                      |                                        |
+	 * |__PCLUSTER_FOLLOWED___|___________PCLUSTER_FOLLOWED____________|
+	 *
+	 * [  (*) the above page can be used as inplace I/O.               ]
+	 */
+	Z_EROFS_PCLUSTER_FOLLOWED,
+};
+
+struct z_erofs_decompress_frontend {
+	struct inode *const inode;
+	struct erofs_map_blocks map;
+	struct z_erofs_bvec_iter biter;
+
+	struct page *candidate_bvpage;
+	struct z_erofs_pcluster *pcl;
+	z_erofs_next_pcluster_t owned_head;
+	enum z_erofs_pclustermode mode;
+
+	bool readahead;
+	/* used for applying cache strategy on the fly */
+	bool backmost;
+	erofs_off_t headoffset;
+
+	/* a pointer used to pick up inplace I/O pages */
+	unsigned int icur;
+};
+
+#define DECOMPRESS_FRONTEND_INIT(__i) { \
+	.inode = __i, .owned_head = Z_EROFS_PCLUSTER_TAIL, \
+	.mode = Z_EROFS_PCLUSTER_FOLLOWED, .backmost = true }
+
+static bool z_erofs_should_alloc_cache(struct z_erofs_decompress_frontend *fe)
+{
+	unsigned int cachestrategy = EROFS_I_SB(fe->inode)->opt.cache_strategy;
+
+	if (cachestrategy <= EROFS_ZIP_CACHE_DISABLED)
+		return false;
+
+	if (fe->backmost)
+		return true;
+
+	if (cachestrategy >= EROFS_ZIP_CACHE_READAROUND &&
+	    fe->map.m_la < fe->headoffset)
+		return true;
+
+	return false;
+}
+
+static void z_erofs_bind_cache(struct z_erofs_decompress_frontend *fe,
+			       struct page **pagepool)
+{
+	struct address_space *mc = MNGD_MAPPING(EROFS_I_SB(fe->inode));
+	struct z_erofs_pcluster *pcl = fe->pcl;
+	bool shouldalloc = z_erofs_should_alloc_cache(fe);
+	bool standalone = true;
+	/*
+	 * optimistic allocation without direct reclaim since inplace I/O
+	 * can be used if low memory otherwise.
+	 */
+	gfp_t gfp = (mapping_gfp_mask(mc) & ~__GFP_DIRECT_RECLAIM) |
+			__GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN;
+	unsigned int i;
+
+	if (fe->mode < Z_EROFS_PCLUSTER_FOLLOWED)
+		return;
+
+	for (i = 0; i < pcl->pclusterpages; ++i) {
+		struct page *page;
+		void *t;	/* mark pages just found for debugging */
+		struct page *newpage = NULL;
+
+		/* the compressed page was loaded before */
+		if (READ_ONCE(pcl->compressed_bvecs[i].page))
+			continue;
+
+		page = find_get_page(mc, pcl->obj.index + i);
+
+		if (page) {
+			t = (void *)((unsigned long)page | 1);
+		} else {
+			/* I/O is needed, no possible to decompress directly */
+			standalone = false;
+			if (!shouldalloc)
+				continue;
+
+			/*
+			 * try to use cached I/O if page allocation
+			 * succeeds or fallback to in-place I/O instead
+			 * to avoid any direct reclaim.
+			 */
+			newpage = erofs_allocpage(pagepool, gfp);
+			if (!newpage)
+				continue;
+			set_page_private(newpage, Z_EROFS_PREALLOCATED_PAGE);
+			t = (void *)((unsigned long)newpage | 1);
+		}
+
+		if (!cmpxchg_relaxed(&pcl->compressed_bvecs[i].page, NULL, t))
+			continue;
+
+		if (page)
+			put_page(page);
+		else if (newpage)
+			erofs_pagepool_add(pagepool, newpage);
+	}
+
+	/*
+	 * don't do inplace I/O if all compressed pages are available in
+	 * managed cache since it can be moved to the bypass queue instead.
+	 */
+	if (standalone)
+		fe->mode = Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE;
+}
+
+/* called by erofs_shrinker to get rid of all compressed_pages */
+int erofs_try_to_free_all_cached_pages(struct erofs_sb_info *sbi,
+				       struct erofs_workgroup *grp)
+{
+	struct z_erofs_pcluster *const pcl =
+		container_of(grp, struct z_erofs_pcluster, obj);
+	int i;
+
+	DBG_BUGON(z_erofs_is_inline_pcluster(pcl));
+	/*
+	 * refcount of workgroup is now freezed as 1,
+	 * therefore no need to worry about available decompression users.
+	 */
+	for (i = 0; i < pcl->pclusterpages; ++i) {
+		struct page *page = pcl->compressed_bvecs[i].page;
+
+		if (!page)
+			continue;
+
+		/* block other users from reclaiming or migrating the page */
+		if (!trylock_page(page))
+			return -EBUSY;
+
+		if (!erofs_page_is_managed(sbi, page))
+			continue;
+
+		/* barrier is implied in the following 'unlock_page' */
+		WRITE_ONCE(pcl->compressed_bvecs[i].page, NULL);
+		detach_page_private(page);
+		unlock_page(page);
+	}
+	return 0;
+}
+
+int erofs_try_to_free_cached_page(struct page *page)
+{
+	struct z_erofs_pcluster *const pcl = (void *)page_private(page);
+	int ret, i;
+
+	if (!erofs_workgroup_try_to_freeze(&pcl->obj, 1))
+		return 0;
+
+	ret = 0;
+	DBG_BUGON(z_erofs_is_inline_pcluster(pcl));
+	for (i = 0; i < pcl->pclusterpages; ++i) {
+		if (pcl->compressed_bvecs[i].page == page) {
+			WRITE_ONCE(pcl->compressed_bvecs[i].page, NULL);
+			ret = 1;
+			break;
+		}
+	}
+	erofs_workgroup_unfreeze(&pcl->obj, 1);
+	if (ret)
+		detach_page_private(page);
+	return ret;
+}
+
+static bool z_erofs_try_inplace_io(struct z_erofs_decompress_frontend *fe,
+				   struct z_erofs_bvec *bvec)
+{
+	struct z_erofs_pcluster *const pcl = fe->pcl;
+
+	while (fe->icur > 0) {
+		if (!cmpxchg(&pcl->compressed_bvecs[--fe->icur].page,
+			     NULL, bvec->page)) {
+			pcl->compressed_bvecs[fe->icur] = *bvec;
+			return true;
+		}
+	}
+	return false;
+}
+
+/* callers must be with pcluster lock held */
+static int z_erofs_attach_page(struct z_erofs_decompress_frontend *fe,
+			       struct z_erofs_bvec *bvec, bool exclusive)
+{
+	int ret;
+
+	if (exclusive) {
+		/* give priority for inplaceio to use file pages first */
+		if (z_erofs_try_inplace_io(fe, bvec))
+			return 0;
+		/* otherwise, check if it can be used as a bvpage */
+		if (fe->mode >= Z_EROFS_PCLUSTER_FOLLOWED &&
+		    !fe->candidate_bvpage)
+			fe->candidate_bvpage = bvec->page;
+	}
+	ret = z_erofs_bvec_enqueue(&fe->biter, bvec, &fe->candidate_bvpage);
+	fe->pcl->vcnt += (ret >= 0);
+	return ret;
+}
+
+static void z_erofs_try_to_claim_pcluster(struct z_erofs_decompress_frontend *f)
+{
+	struct z_erofs_pcluster *pcl = f->pcl;
+	z_erofs_next_pcluster_t *owned_head = &f->owned_head;
+
+	/* type 1, nil pcluster (this pcluster doesn't belong to any chain.) */
+	if (cmpxchg(&pcl->next, Z_EROFS_PCLUSTER_NIL,
+		    *owned_head) == Z_EROFS_PCLUSTER_NIL) {
+		*owned_head = &pcl->next;
+		/* so we can attach this pcluster to our submission chain. */
+		f->mode = Z_EROFS_PCLUSTER_FOLLOWED;
+		return;
+	}
+
+	/* type 2, it belongs to an ongoing chain */
+	f->mode = Z_EROFS_PCLUSTER_INFLIGHT;
+}
+
+static int z_erofs_register_pcluster(struct z_erofs_decompress_frontend *fe)
+{
+	struct erofs_map_blocks *map = &fe->map;
+	bool ztailpacking = map->m_flags & EROFS_MAP_META;
+	struct z_erofs_pcluster *pcl;
+	struct erofs_workgroup *grp;
+	int err;
+
+	if (!(map->m_flags & EROFS_MAP_ENCODED) ||
+	    (!ztailpacking && !(map->m_pa >> PAGE_SHIFT))) {
+		DBG_BUGON(1);
+		return -EFSCORRUPTED;
+	}
+
+	/* no available pcluster, let's allocate one */
+	pcl = z_erofs_alloc_pcluster(ztailpacking ? 1 :
+				     map->m_plen >> PAGE_SHIFT);
+	if (IS_ERR(pcl))
+		return PTR_ERR(pcl);
+
+	atomic_set(&pcl->obj.refcount, 1);
+	pcl->algorithmformat = map->m_algorithmformat;
+	pcl->length = 0;
+	pcl->partial = true;
+
+	/* new pclusters should be claimed as type 1, primary and followed */
+	pcl->next = fe->owned_head;
+	pcl->pageofs_out = map->m_la & ~PAGE_MASK;
+	fe->mode = Z_EROFS_PCLUSTER_FOLLOWED;
+
+	/*
+	 * lock all primary followed works before visible to others
+	 * and mutex_trylock *never* fails for a new pcluster.
+	 */
+	mutex_init(&pcl->lock);
+	DBG_BUGON(!mutex_trylock(&pcl->lock));
+
+	if (ztailpacking) {
+		pcl->obj.index = 0;	/* which indicates ztailpacking */
+		pcl->pageofs_in = erofs_blkoff(map->m_pa);
+		pcl->tailpacking_size = map->m_plen;
+	} else {
+		pcl->obj.index = map->m_pa >> PAGE_SHIFT;
+
+		grp = erofs_insert_workgroup(fe->inode->i_sb, &pcl->obj);
+		if (IS_ERR(grp)) {
+			err = PTR_ERR(grp);
+			goto err_out;
+		}
+
+		if (grp != &pcl->obj) {
+			fe->pcl = container_of(grp,
+					struct z_erofs_pcluster, obj);
+			err = -EEXIST;
+			goto err_out;
+		}
+	}
+	fe->owned_head = &pcl->next;
+	fe->pcl = pcl;
+	return 0;
+
+err_out:
+	mutex_unlock(&pcl->lock);
+	z_erofs_free_pcluster(pcl);
+	return err;
+}
+
+static int z_erofs_collector_begin(struct z_erofs_decompress_frontend *fe)
+{
+	struct erofs_map_blocks *map = &fe->map;
+	struct erofs_workgroup *grp = NULL;
+	int ret;
+
+	DBG_BUGON(fe->pcl);
+
+	/* must be Z_EROFS_PCLUSTER_TAIL or pointed to previous pcluster */
+	DBG_BUGON(fe->owned_head == Z_EROFS_PCLUSTER_NIL);
+
+	if (!(map->m_flags & EROFS_MAP_META)) {
+		grp = erofs_find_workgroup(fe->inode->i_sb,
+					   map->m_pa >> PAGE_SHIFT);
+	} else if ((map->m_pa & ~PAGE_MASK) + map->m_plen > PAGE_SIZE) {
+		DBG_BUGON(1);
+		return -EFSCORRUPTED;
+	}
+
+	if (grp) {
+		fe->pcl = container_of(grp, struct z_erofs_pcluster, obj);
+		ret = -EEXIST;
+	} else {
+		ret = z_erofs_register_pcluster(fe);
+	}
+
+	if (ret == -EEXIST) {
+		mutex_lock(&fe->pcl->lock);
+		z_erofs_try_to_claim_pcluster(fe);
+	} else if (ret) {
+		return ret;
+	}
+	z_erofs_bvec_iter_begin(&fe->biter, &fe->pcl->bvset,
+				Z_EROFS_INLINE_BVECS, fe->pcl->vcnt);
+	/* since file-backed online pages are traversed in reverse order */
+	fe->icur = z_erofs_pclusterpages(fe->pcl);
+	return 0;
+}
+
+/*
+ * keep in mind that no referenced pclusters will be freed
+ * only after a RCU grace period.
+ */
+static void z_erofs_rcu_callback(struct rcu_head *head)
+{
+	z_erofs_free_pcluster(container_of(head,
+			struct z_erofs_pcluster, rcu));
+}
+
+void erofs_workgroup_free_rcu(struct erofs_workgroup *grp)
+{
+	struct z_erofs_pcluster *const pcl =
+		container_of(grp, struct z_erofs_pcluster, obj);
+
+	call_rcu(&pcl->rcu, z_erofs_rcu_callback);
+}
+
+static bool z_erofs_collector_end(struct z_erofs_decompress_frontend *fe)
+{
+	struct z_erofs_pcluster *pcl = fe->pcl;
+
+	if (!pcl)
+		return false;
+
+	z_erofs_bvec_iter_end(&fe->biter);
+	mutex_unlock(&pcl->lock);
+
+	if (fe->candidate_bvpage) {
+		DBG_BUGON(z_erofs_is_shortlived_page(fe->candidate_bvpage));
+		fe->candidate_bvpage = NULL;
+	}
+
+	/*
+	 * if all pending pages are added, don't hold its reference
+	 * any longer if the pcluster isn't hosted by ourselves.
+	 */
+	if (fe->mode < Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE)
+		erofs_workgroup_put(&pcl->obj);
+
+	fe->pcl = NULL;
+	return true;
+}
+
+static int z_erofs_read_fragment(struct inode *inode, erofs_off_t pos,
+				 struct page *page, unsigned int pageofs,
+				 unsigned int len)
+{
+	struct inode *packed_inode = EROFS_I_SB(inode)->packed_inode;
+	struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
+	u8 *src, *dst;
+	unsigned int i, cnt;
+
+	if (!packed_inode)
+		return -EFSCORRUPTED;
+
+	pos += EROFS_I(inode)->z_fragmentoff;
+	for (i = 0; i < len; i += cnt) {
+		cnt = min_t(unsigned int, len - i,
+			    EROFS_BLKSIZ - erofs_blkoff(pos));
+		src = erofs_bread(&buf, packed_inode,
+				  erofs_blknr(pos), EROFS_KMAP);
+		if (IS_ERR(src)) {
+			erofs_put_metabuf(&buf);
+			return PTR_ERR(src);
+		}
+
+		dst = kmap_local_page(page);
+		memcpy(dst + pageofs + i, src + erofs_blkoff(pos), cnt);
+		kunmap_local(dst);
+		pos += cnt;
+	}
+	erofs_put_metabuf(&buf);
+	return 0;
+}
+
+static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
+				struct page *page, struct page **pagepool)
+{
+	struct inode *const inode = fe->inode;
+	struct erofs_map_blocks *const map = &fe->map;
+	const loff_t offset = page_offset(page);
+	bool tight = true, exclusive;
+	unsigned int cur, end, spiltted;
+	int err = 0;
+
+	/* register locked file pages as online pages in pack */
+	z_erofs_onlinepage_init(page);
+
+	spiltted = 0;
+	end = PAGE_SIZE;
+repeat:
+	cur = end - 1;
+
+	if (offset + cur < map->m_la ||
+	    offset + cur >= map->m_la + map->m_llen) {
+		erofs_dbg("out-of-range map @ pos %llu", offset + cur);
+
+		if (z_erofs_collector_end(fe))
+			fe->backmost = false;
+		map->m_la = offset + cur;
+		map->m_llen = 0;
+		err = z_erofs_map_blocks_iter(inode, map, 0);
+		if (err)
+			goto out;
+	} else {
+		if (fe->pcl)
+			goto hitted;
+		/* didn't get a valid pcluster previously (very rare) */
+	}
+
+	if (!(map->m_flags & EROFS_MAP_MAPPED) ||
+	    map->m_flags & EROFS_MAP_FRAGMENT)
+		goto hitted;
+
+	err = z_erofs_collector_begin(fe);
+	if (err)
+		goto out;
+
+	if (z_erofs_is_inline_pcluster(fe->pcl)) {
+		void *mp;
+
+		mp = erofs_read_metabuf(&fe->map.buf, inode->i_sb,
+					erofs_blknr(map->m_pa), EROFS_NO_KMAP);
+		if (IS_ERR(mp)) {
+			err = PTR_ERR(mp);
+			erofs_err(inode->i_sb,
+				  "failed to get inline page, err %d", err);
+			goto out;
+		}
+		get_page(fe->map.buf.page);
+		WRITE_ONCE(fe->pcl->compressed_bvecs[0].page,
+			   fe->map.buf.page);
+		fe->mode = Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE;
+	} else {
+		/* bind cache first when cached decompression is preferred */
+		z_erofs_bind_cache(fe, pagepool);
+	}
+hitted:
+	/*
+	 * Ensure the current partial page belongs to this submit chain rather
+	 * than other concurrent submit chains or the noio(bypass) chain since
+	 * those chains are handled asynchronously thus the page cannot be used
+	 * for inplace I/O or bvpage (should be processed in a strict order.)
+	 */
+	tight &= (fe->mode > Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE);
+
+	cur = end - min_t(erofs_off_t, offset + end - map->m_la, end);
+	if (!(map->m_flags & EROFS_MAP_MAPPED)) {
+		zero_user_segment(page, cur, end);
+		++spiltted;
+		tight = false;
+		goto next_part;
+	}
+	if (map->m_flags & EROFS_MAP_FRAGMENT) {
+		unsigned int pageofs, skip, len;
+
+		if (offset > map->m_la) {
+			pageofs = 0;
+			skip = offset - map->m_la;
+		} else {
+			pageofs = map->m_la & ~PAGE_MASK;
+			skip = 0;
+		}
+		len = min_t(unsigned int, map->m_llen - skip, end - cur);
+		err = z_erofs_read_fragment(inode, skip, page, pageofs, len);
+		if (err)
+			goto out;
+		++spiltted;
+		tight = false;
+		goto next_part;
+	}
+
+	exclusive = (!cur && (!spiltted || tight));
+	if (cur)
+		tight &= (fe->mode >= Z_EROFS_PCLUSTER_FOLLOWED);
+
+retry:
+	err = z_erofs_attach_page(fe, &((struct z_erofs_bvec) {
+					.page = page,
+					.offset = offset - map->m_la,
+					.end = end,
+				  }), exclusive);
+	/* should allocate an additional short-lived page for bvset */
+	if (err == -EAGAIN && !fe->candidate_bvpage) {
+		fe->candidate_bvpage = alloc_page(GFP_NOFS | __GFP_NOFAIL);
+		set_page_private(fe->candidate_bvpage,
+				 Z_EROFS_SHORTLIVED_PAGE);
+		goto retry;
+	}
+
+	if (err) {
+		DBG_BUGON(err == -EAGAIN && fe->candidate_bvpage);
+		goto out;
+	}
+
+	z_erofs_onlinepage_split(page);
+	/* bump up the number of spiltted parts of a page */
+	++spiltted;
+	if (fe->pcl->pageofs_out != (map->m_la & ~PAGE_MASK))
+		fe->pcl->multibases = true;
+	if (fe->pcl->length < offset + end - map->m_la) {
+		fe->pcl->length = offset + end - map->m_la;
+		fe->pcl->pageofs_out = map->m_la & ~PAGE_MASK;
+	}
+	if ((map->m_flags & EROFS_MAP_FULL_MAPPED) &&
+	    !(map->m_flags & EROFS_MAP_PARTIAL_REF) &&
+	    fe->pcl->length == map->m_llen)
+		fe->pcl->partial = false;
+next_part:
+	/* shorten the remaining extent to update progress */
+	map->m_llen = offset + cur - map->m_la;
+	map->m_flags &= ~EROFS_MAP_FULL_MAPPED;
+
+	end = cur;
+	if (end > 0)
+		goto repeat;
+
+out:
+	if (err)
+		z_erofs_page_mark_eio(page);
+	z_erofs_onlinepage_endio(page);
+
+	erofs_dbg("%s, finish page: %pK spiltted: %u map->m_llen %llu",
+		  __func__, page, spiltted, map->m_llen);
+	return err;
+}
+
+static bool z_erofs_get_sync_decompress_policy(struct erofs_sb_info *sbi,
+				       unsigned int readahead_pages)
+{
+	/* auto: enable for read_folio, disable for readahead */
+	if ((sbi->opt.sync_decompress == EROFS_SYNC_DECOMPRESS_AUTO) &&
+	    !readahead_pages)
+		return true;
+
+	if ((sbi->opt.sync_decompress == EROFS_SYNC_DECOMPRESS_FORCE_ON) &&
+	    (readahead_pages <= sbi->opt.max_sync_decompress_pages))
+		return true;
+
+	return false;
+}
+
+static bool z_erofs_page_is_invalidated(struct page *page)
+{
+	return !page->mapping && !z_erofs_is_shortlived_page(page);
+}
+
+struct z_erofs_decompress_backend {
+	struct page *onstack_pages[Z_EROFS_ONSTACK_PAGES];
+	struct super_block *sb;
+	struct z_erofs_pcluster *pcl;
+
+	/* pages with the longest decompressed length for deduplication */
+	struct page **decompressed_pages;
+	/* pages to keep the compressed data */
+	struct page **compressed_pages;
+
+	struct list_head decompressed_secondary_bvecs;
+	struct page **pagepool;
+	unsigned int onstack_used, nr_pages;
+};
+
+struct z_erofs_bvec_item {
+	struct z_erofs_bvec bvec;
+	struct list_head list;
+};
+
+static void z_erofs_do_decompressed_bvec(struct z_erofs_decompress_backend *be,
+					 struct z_erofs_bvec *bvec)
+{
+	struct z_erofs_bvec_item *item;
+	unsigned int pgnr;
+
+	if (!((bvec->offset + be->pcl->pageofs_out) & ~PAGE_MASK) &&
+	    (bvec->end == PAGE_SIZE ||
+	     bvec->offset + bvec->end == be->pcl->length)) {
+		pgnr = (bvec->offset + be->pcl->pageofs_out) >> PAGE_SHIFT;
+		DBG_BUGON(pgnr >= be->nr_pages);
+		if (!be->decompressed_pages[pgnr]) {
+			be->decompressed_pages[pgnr] = bvec->page;
+			return;
+		}
+	}
+
+	/* (cold path) one pcluster is requested multiple times */
+	item = kmalloc(sizeof(*item), GFP_KERNEL | __GFP_NOFAIL);
+	item->bvec = *bvec;
+	list_add(&item->list, &be->decompressed_secondary_bvecs);
+}
+
+static void z_erofs_fill_other_copies(struct z_erofs_decompress_backend *be,
+				      int err)
+{
+	unsigned int off0 = be->pcl->pageofs_out;
+	struct list_head *p, *n;
+
+	list_for_each_safe(p, n, &be->decompressed_secondary_bvecs) {
+		struct z_erofs_bvec_item *bvi;
+		unsigned int end, cur;
+		void *dst, *src;
+
+		bvi = container_of(p, struct z_erofs_bvec_item, list);
+		cur = bvi->bvec.offset < 0 ? -bvi->bvec.offset : 0;
+		end = min_t(unsigned int, be->pcl->length - bvi->bvec.offset,
+			    bvi->bvec.end);
+		dst = kmap_local_page(bvi->bvec.page);
+		while (cur < end) {
+			unsigned int pgnr, scur, len;
+
+			pgnr = (bvi->bvec.offset + cur + off0) >> PAGE_SHIFT;
+			DBG_BUGON(pgnr >= be->nr_pages);
+
+			scur = bvi->bvec.offset + cur -
+					((pgnr << PAGE_SHIFT) - off0);
+			len = min_t(unsigned int, end - cur, PAGE_SIZE - scur);
+			if (!be->decompressed_pages[pgnr]) {
+				err = -EFSCORRUPTED;
+				cur += len;
+				continue;
+			}
+			src = kmap_local_page(be->decompressed_pages[pgnr]);
+			memcpy(dst + cur, src + scur, len);
+			kunmap_local(src);
+			cur += len;
+		}
+		kunmap_local(dst);
+		if (err)
+			z_erofs_page_mark_eio(bvi->bvec.page);
+		z_erofs_onlinepage_endio(bvi->bvec.page);
+		list_del(p);
+		kfree(bvi);
+	}
+}
+
+static void z_erofs_parse_out_bvecs(struct z_erofs_decompress_backend *be)
+{
+	struct z_erofs_pcluster *pcl = be->pcl;
+	struct z_erofs_bvec_iter biter;
+	struct page *old_bvpage;
+	int i;
+
+	z_erofs_bvec_iter_begin(&biter, &pcl->bvset, Z_EROFS_INLINE_BVECS, 0);
+	for (i = 0; i < pcl->vcnt; ++i) {
+		struct z_erofs_bvec bvec;
+
+		z_erofs_bvec_dequeue(&biter, &bvec, &old_bvpage);
+
+		if (old_bvpage)
+			z_erofs_put_shortlivedpage(be->pagepool, old_bvpage);
+
+		DBG_BUGON(z_erofs_page_is_invalidated(bvec.page));
+		z_erofs_do_decompressed_bvec(be, &bvec);
+	}
+
+	old_bvpage = z_erofs_bvec_iter_end(&biter);
+	if (old_bvpage)
+		z_erofs_put_shortlivedpage(be->pagepool, old_bvpage);
+}
+
+static int z_erofs_parse_in_bvecs(struct z_erofs_decompress_backend *be,
+				  bool *overlapped)
+{
+	struct z_erofs_pcluster *pcl = be->pcl;
+	unsigned int pclusterpages = z_erofs_pclusterpages(pcl);
+	int i, err = 0;
+
+	*overlapped = false;
+	for (i = 0; i < pclusterpages; ++i) {
+		struct z_erofs_bvec *bvec = &pcl->compressed_bvecs[i];
+		struct page *page = bvec->page;
+
+		/* compressed pages ought to be present before decompressing */
+		if (!page) {
+			DBG_BUGON(1);
+			continue;
+		}
+		be->compressed_pages[i] = page;
+
+		if (z_erofs_is_inline_pcluster(pcl)) {
+			if (!PageUptodate(page))
+				err = -EIO;
+			continue;
+		}
+
+		DBG_BUGON(z_erofs_page_is_invalidated(page));
+		if (!z_erofs_is_shortlived_page(page)) {
+			if (erofs_page_is_managed(EROFS_SB(be->sb), page)) {
+				if (!PageUptodate(page))
+					err = -EIO;
+				continue;
+			}
+			z_erofs_do_decompressed_bvec(be, bvec);
+			*overlapped = true;
+		}
+	}
+
+	if (err)
+		return err;
+	return 0;
+}
+
+static int z_erofs_decompress_pcluster(struct z_erofs_decompress_backend *be,
+				       int err)
+{
+	struct erofs_sb_info *const sbi = EROFS_SB(be->sb);
+	struct z_erofs_pcluster *pcl = be->pcl;
+	unsigned int pclusterpages = z_erofs_pclusterpages(pcl);
+	unsigned int i, inputsize;
+	int err2;
+	struct page *page;
+	bool overlapped;
+
+	mutex_lock(&pcl->lock);
+	be->nr_pages = PAGE_ALIGN(pcl->length + pcl->pageofs_out) >> PAGE_SHIFT;
+
+	/* allocate (de)compressed page arrays if cannot be kept on stack */
+	be->decompressed_pages = NULL;
+	be->compressed_pages = NULL;
+	be->onstack_used = 0;
+	if (be->nr_pages <= Z_EROFS_ONSTACK_PAGES) {
+		be->decompressed_pages = be->onstack_pages;
+		be->onstack_used = be->nr_pages;
+		memset(be->decompressed_pages, 0,
+		       sizeof(struct page *) * be->nr_pages);
+	}
+
+	if (pclusterpages + be->onstack_used <= Z_EROFS_ONSTACK_PAGES)
+		be->compressed_pages = be->onstack_pages + be->onstack_used;
+
+	if (!be->decompressed_pages)
+		be->decompressed_pages =
+			kvcalloc(be->nr_pages, sizeof(struct page *),
+				 GFP_KERNEL | __GFP_NOFAIL);
+	if (!be->compressed_pages)
+		be->compressed_pages =
+			kvcalloc(pclusterpages, sizeof(struct page *),
+				 GFP_KERNEL | __GFP_NOFAIL);
+
+	z_erofs_parse_out_bvecs(be);
+	err2 = z_erofs_parse_in_bvecs(be, &overlapped);
+	if (err2)
+		err = err2;
+	if (err)
+		goto out;
+
+	if (z_erofs_is_inline_pcluster(pcl))
+		inputsize = pcl->tailpacking_size;
+	else
+		inputsize = pclusterpages * PAGE_SIZE;
+
+	err = z_erofs_decompress(&(struct z_erofs_decompress_req) {
+					.sb = be->sb,
+					.in = be->compressed_pages,
+					.out = be->decompressed_pages,
+					.pageofs_in = pcl->pageofs_in,
+					.pageofs_out = pcl->pageofs_out,
+					.inputsize = inputsize,
+					.outputsize = pcl->length,
+					.alg = pcl->algorithmformat,
+					.inplace_io = overlapped,
+					.partial_decoding = pcl->partial,
+					.fillgaps = pcl->multibases,
+				 }, be->pagepool);
+
+out:
+	/* must handle all compressed pages before actual file pages */
+	if (z_erofs_is_inline_pcluster(pcl)) {
+		page = pcl->compressed_bvecs[0].page;
+		WRITE_ONCE(pcl->compressed_bvecs[0].page, NULL);
+		put_page(page);
+	} else {
+		for (i = 0; i < pclusterpages; ++i) {
+			/* consider shortlived pages added when decompressing */
+			page = be->compressed_pages[i];
+
+			if (erofs_page_is_managed(sbi, page))
+				continue;
+			(void)z_erofs_put_shortlivedpage(be->pagepool, page);
+			WRITE_ONCE(pcl->compressed_bvecs[i].page, NULL);
+		}
+	}
+	if (be->compressed_pages < be->onstack_pages ||
+	    be->compressed_pages >= be->onstack_pages + Z_EROFS_ONSTACK_PAGES)
+		kvfree(be->compressed_pages);
+	z_erofs_fill_other_copies(be, err);
+
+	for (i = 0; i < be->nr_pages; ++i) {
+		page = be->decompressed_pages[i];
+		if (!page)
+			continue;
+
+		DBG_BUGON(z_erofs_page_is_invalidated(page));
+
+		/* recycle all individual short-lived pages */
+		if (z_erofs_put_shortlivedpage(be->pagepool, page))
+			continue;
+		if (err)
+			z_erofs_page_mark_eio(page);
+		z_erofs_onlinepage_endio(page);
+	}
+
+	if (be->decompressed_pages != be->onstack_pages)
+		kvfree(be->decompressed_pages);
+
+	pcl->length = 0;
+	pcl->partial = true;
+	pcl->multibases = false;
+	pcl->bvset.nextpage = NULL;
+	pcl->vcnt = 0;
+
+	/* pcluster lock MUST be taken before the following line */
+	WRITE_ONCE(pcl->next, Z_EROFS_PCLUSTER_NIL);
+	mutex_unlock(&pcl->lock);
+	return err;
+}
+
+static void z_erofs_decompress_queue(const struct z_erofs_decompressqueue *io,
+				     struct page **pagepool)
+{
+	struct z_erofs_decompress_backend be = {
+		.sb = io->sb,
+		.pagepool = pagepool,
+		.decompressed_secondary_bvecs =
+			LIST_HEAD_INIT(be.decompressed_secondary_bvecs),
+	};
+	z_erofs_next_pcluster_t owned = io->head;
+
+	while (owned != Z_EROFS_PCLUSTER_TAIL) {
+		DBG_BUGON(owned == Z_EROFS_PCLUSTER_NIL);
+
+		be.pcl = container_of(owned, struct z_erofs_pcluster, next);
+		owned = READ_ONCE(be.pcl->next);
+
+		z_erofs_decompress_pcluster(&be, io->eio ? -EIO : 0);
+		erofs_workgroup_put(&be.pcl->obj);
+	}
+}
+
+static void z_erofs_decompressqueue_work(struct work_struct *work)
+{
+	struct z_erofs_decompressqueue *bgq =
+		container_of(work, struct z_erofs_decompressqueue, u.work);
+	struct page *pagepool = NULL;
+
+	DBG_BUGON(bgq->head == Z_EROFS_PCLUSTER_TAIL);
+	z_erofs_decompress_queue(bgq, &pagepool);
+
+	erofs_release_pages(&pagepool);
+	kvfree(bgq);
+}
+
+static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
+				       int bios)
+{
+	struct erofs_sb_info *const sbi = EROFS_SB(io->sb);
+
+	/* wake up the caller thread for sync decompression */
+	if (io->sync) {
+		if (!atomic_add_return(bios, &io->pending_bios))
+			complete(&io->u.done);
+		return;
+	}
+
+	if (atomic_add_return(bios, &io->pending_bios))
+		return;
+	/* Use workqueue and sync decompression for atomic contexts only */
+	if (in_atomic() || irqs_disabled()) {
+		queue_work(z_erofs_workqueue, &io->u.work);
+		/* enable sync decompression for readahead */
+		if (sbi->opt.sync_decompress == EROFS_SYNC_DECOMPRESS_AUTO)
+			sbi->opt.sync_decompress = EROFS_SYNC_DECOMPRESS_FORCE_ON;
+		return;
+	}
+	z_erofs_decompressqueue_work(&io->u.work);
+}
+
+static struct page *pickup_page_for_submission(struct z_erofs_pcluster *pcl,
+					       unsigned int nr,
+					       struct page **pagepool,
+					       struct address_space *mc)
+{
+	const pgoff_t index = pcl->obj.index;
+	gfp_t gfp = mapping_gfp_mask(mc);
+	bool tocache = false;
+
+	struct address_space *mapping;
+	struct page *oldpage, *page;
+	int justfound;
+
+repeat:
+	page = READ_ONCE(pcl->compressed_bvecs[nr].page);
+	oldpage = page;
+
+	if (!page)
+		goto out_allocpage;
+
+	justfound = (unsigned long)page & 1UL;
+	page = (struct page *)((unsigned long)page & ~1UL);
+
+	/*
+	 * preallocated cached pages, which is used to avoid direct reclaim
+	 * otherwise, it will go inplace I/O path instead.
+	 */
+	if (page->private == Z_EROFS_PREALLOCATED_PAGE) {
+		WRITE_ONCE(pcl->compressed_bvecs[nr].page, page);
+		set_page_private(page, 0);
+		tocache = true;
+		goto out_tocache;
+	}
+	mapping = READ_ONCE(page->mapping);
+
+	/*
+	 * file-backed online pages in plcuster are all locked steady,
+	 * therefore it is impossible for `mapping' to be NULL.
+	 */
+	if (mapping && mapping != mc)
+		/* ought to be unmanaged pages */
+		goto out;
+
+	/* directly return for shortlived page as well */
+	if (z_erofs_is_shortlived_page(page))
+		goto out;
+
+	lock_page(page);
+
+	/* only true if page reclaim goes wrong, should never happen */
+	DBG_BUGON(justfound && PagePrivate(page));
+
+	/* the page is still in manage cache */
+	if (page->mapping == mc) {
+		WRITE_ONCE(pcl->compressed_bvecs[nr].page, page);
+
+		if (!PagePrivate(page)) {
+			/*
+			 * impossible to be !PagePrivate(page) for
+			 * the current restriction as well if
+			 * the page is already in compressed_bvecs[].
+			 */
+			DBG_BUGON(!justfound);
+
+			justfound = 0;
+			set_page_private(page, (unsigned long)pcl);
+			SetPagePrivate(page);
+		}
+
+		/* no need to submit io if it is already up-to-date */
+		if (PageUptodate(page)) {
+			unlock_page(page);
+			page = NULL;
+		}
+		goto out;
+	}
+
+	/*
+	 * the managed page has been truncated, it's unsafe to
+	 * reuse this one, let's allocate a new cache-managed page.
+	 */
+	DBG_BUGON(page->mapping);
+	DBG_BUGON(!justfound);
+
+	tocache = true;
+	unlock_page(page);
+	put_page(page);
+out_allocpage:
+	page = erofs_allocpage(pagepool, gfp | __GFP_NOFAIL);
+	if (oldpage != cmpxchg(&pcl->compressed_bvecs[nr].page,
+			       oldpage, page)) {
+		erofs_pagepool_add(pagepool, page);
+		cond_resched();
+		goto repeat;
+	}
+out_tocache:
+	if (!tocache || add_to_page_cache_lru(page, mc, index + nr, gfp)) {
+		/* turn into temporary page if fails (1 ref) */
+		set_page_private(page, Z_EROFS_SHORTLIVED_PAGE);
+		goto out;
+	}
+	attach_page_private(page, pcl);
+	/* drop a refcount added by allocpage (then we have 2 refs here) */
+	put_page(page);
+
+out:	/* the only exit (for tracing and debugging) */
+	return page;
+}
+
+static struct z_erofs_decompressqueue *jobqueue_init(struct super_block *sb,
+			      struct z_erofs_decompressqueue *fgq, bool *fg)
+{
+	struct z_erofs_decompressqueue *q;
+
+	if (fg && !*fg) {
+		q = kvzalloc(sizeof(*q), GFP_KERNEL | __GFP_NOWARN);
+		if (!q) {
+			*fg = true;
+			goto fg_out;
+		}
+		INIT_WORK(&q->u.work, z_erofs_decompressqueue_work);
+	} else {
+fg_out:
+		q = fgq;
+		init_completion(&fgq->u.done);
+		atomic_set(&fgq->pending_bios, 0);
+		q->eio = false;
+		q->sync = true;
+	}
+	q->sb = sb;
+	q->head = Z_EROFS_PCLUSTER_TAIL;
+	return q;
+}
+
+/* define decompression jobqueue types */
+enum {
+	JQ_BYPASS,
+	JQ_SUBMIT,
+	NR_JOBQUEUES,
+};
+
+static void move_to_bypass_jobqueue(struct z_erofs_pcluster *pcl,
+				    z_erofs_next_pcluster_t qtail[],
+				    z_erofs_next_pcluster_t owned_head)
+{
+	z_erofs_next_pcluster_t *const submit_qtail = qtail[JQ_SUBMIT];
+	z_erofs_next_pcluster_t *const bypass_qtail = qtail[JQ_BYPASS];
+
+	WRITE_ONCE(pcl->next, Z_EROFS_PCLUSTER_TAIL);
+
+	WRITE_ONCE(*submit_qtail, owned_head);
+	WRITE_ONCE(*bypass_qtail, &pcl->next);
+
+	qtail[JQ_BYPASS] = &pcl->next;
+}
+
+static void z_erofs_decompressqueue_endio(struct bio *bio)
+{
+	struct z_erofs_decompressqueue *q = bio->bi_private;
+	blk_status_t err = bio->bi_status;
+	struct bio_vec *bvec;
+	struct bvec_iter_all iter_all;
+
+	bio_for_each_segment_all(bvec, bio, iter_all) {
+		struct page *page = bvec->bv_page;
+
+		DBG_BUGON(PageUptodate(page));
+		DBG_BUGON(z_erofs_page_is_invalidated(page));
+
+		if (erofs_page_is_managed(EROFS_SB(q->sb), page)) {
+			if (!err)
+				SetPageUptodate(page);
+			unlock_page(page);
+		}
+	}
+	if (err)
+		q->eio = true;
+	z_erofs_decompress_kickoff(q, -1);
+	bio_put(bio);
+}
+
+static void z_erofs_submit_queue(struct z_erofs_decompress_frontend *f,
+				 struct page **pagepool,
+				 struct z_erofs_decompressqueue *fgq,
+				 bool *force_fg)
+{
+	struct super_block *sb = f->inode->i_sb;
+	struct address_space *mc = MNGD_MAPPING(EROFS_SB(sb));
+	z_erofs_next_pcluster_t qtail[NR_JOBQUEUES];
+	struct z_erofs_decompressqueue *q[NR_JOBQUEUES];
+	z_erofs_next_pcluster_t owned_head = f->owned_head;
+	/* bio is NULL initially, so no need to initialize last_{index,bdev} */
+	pgoff_t last_index;
+	struct block_device *last_bdev;
+	unsigned int nr_bios = 0;
+	struct bio *bio = NULL;
+	unsigned long pflags;
+	int memstall = 0;
+
+	/*
+	 * if managed cache is enabled, bypass jobqueue is needed,
+	 * no need to read from device for all pclusters in this queue.
+	 */
+	q[JQ_BYPASS] = jobqueue_init(sb, fgq + JQ_BYPASS, NULL);
+	q[JQ_SUBMIT] = jobqueue_init(sb, fgq + JQ_SUBMIT, force_fg);
+
+	qtail[JQ_BYPASS] = &q[JQ_BYPASS]->head;
+	qtail[JQ_SUBMIT] = &q[JQ_SUBMIT]->head;
+
+	/* by default, all need io submission */
+	q[JQ_SUBMIT]->head = owned_head;
+
+	do {
+		struct erofs_map_dev mdev;
+		struct z_erofs_pcluster *pcl;
+		pgoff_t cur, end;
+		unsigned int i = 0;
+		bool bypass = true;
+
+		DBG_BUGON(owned_head == Z_EROFS_PCLUSTER_NIL);
+		pcl = container_of(owned_head, struct z_erofs_pcluster, next);
+		owned_head = READ_ONCE(pcl->next);
+
+		if (z_erofs_is_inline_pcluster(pcl)) {
+			move_to_bypass_jobqueue(pcl, qtail, owned_head);
+			continue;
+		}
+
+		/* no device id here, thus it will always succeed */
+		mdev = (struct erofs_map_dev) {
+			.m_pa = blknr_to_addr(pcl->obj.index),
+		};
+		(void)erofs_map_dev(sb, &mdev);
+
+		cur = erofs_blknr(mdev.m_pa);
+		end = cur + pcl->pclusterpages;
+
+		do {
+			struct page *page;
+
+			page = pickup_page_for_submission(pcl, i++, pagepool,
+							  mc);
+			if (!page)
+				continue;
+
+			if (bio && (cur != last_index + 1 ||
+				    last_bdev != mdev.m_bdev)) {
+submit_bio_retry:
+				submit_bio(bio);
+				if (memstall) {
+					psi_memstall_leave(&pflags);
+					memstall = 0;
+				}
+				bio = NULL;
+			}
+
+			if (unlikely(PageWorkingset(page)) && !memstall) {
+				psi_memstall_enter(&pflags);
+				memstall = 1;
+			}
+
+			if (!bio) {
+				bio = bio_alloc(mdev.m_bdev, BIO_MAX_VECS,
+						REQ_OP_READ, GFP_NOIO);
+				bio->bi_end_io = z_erofs_decompressqueue_endio;
+
+				last_bdev = mdev.m_bdev;
+				bio->bi_iter.bi_sector = (sector_t)cur <<
+					LOG_SECTORS_PER_BLOCK;
+				bio->bi_private = q[JQ_SUBMIT];
+				if (f->readahead)
+					bio->bi_opf |= REQ_RAHEAD;
+				++nr_bios;
+			}
+
+			if (bio_add_page(bio, page, PAGE_SIZE, 0) < PAGE_SIZE)
+				goto submit_bio_retry;
+
+			last_index = cur;
+			bypass = false;
+		} while (++cur < end);
+
+		if (!bypass)
+			qtail[JQ_SUBMIT] = &pcl->next;
+		else
+			move_to_bypass_jobqueue(pcl, qtail, owned_head);
+	} while (owned_head != Z_EROFS_PCLUSTER_TAIL);
+
+	if (bio) {
+		submit_bio(bio);
+		if (memstall)
+			psi_memstall_leave(&pflags);
+	}
+
+	/*
+	 * although background is preferred, no one is pending for submission.
+	 * don't issue workqueue for decompression but drop it directly instead.
+	 */
+	if (!*force_fg && !nr_bios) {
+		kvfree(q[JQ_SUBMIT]);
+		return;
+	}
+	z_erofs_decompress_kickoff(q[JQ_SUBMIT], nr_bios);
+}
+
+static void z_erofs_runqueue(struct z_erofs_decompress_frontend *f,
+			     struct page **pagepool, bool force_fg)
+{
+	struct z_erofs_decompressqueue io[NR_JOBQUEUES];
+
+	if (f->owned_head == Z_EROFS_PCLUSTER_TAIL)
+		return;
+	z_erofs_submit_queue(f, pagepool, io, &force_fg);
+
+	/* handle bypass queue (no i/o pclusters) immediately */
+	z_erofs_decompress_queue(&io[JQ_BYPASS], pagepool);
+
+	if (!force_fg)
+		return;
+
+	/* wait until all bios are completed */
+	wait_for_completion_io(&io[JQ_SUBMIT].u.done);
+
+	/* handle synchronous decompress queue in the caller context */
+	z_erofs_decompress_queue(&io[JQ_SUBMIT], pagepool);
+}
+
+/*
+ * Since partial uptodate is still unimplemented for now, we have to use
+ * approximate readmore strategies as a start.
+ */
+static void z_erofs_pcluster_readmore(struct z_erofs_decompress_frontend *f,
+				      struct readahead_control *rac,
+				      erofs_off_t end,
+				      struct page **pagepool,
+				      bool backmost)
+{
+	struct inode *inode = f->inode;
+	struct erofs_map_blocks *map = &f->map;
+	erofs_off_t cur;
+	int err;
+
+	if (backmost) {
+		map->m_la = end;
+		err = z_erofs_map_blocks_iter(inode, map,
+					      EROFS_GET_BLOCKS_READMORE);
+		if (err)
+			return;
+
+		/* expend ra for the trailing edge if readahead */
+		if (rac) {
+			loff_t newstart = readahead_pos(rac);
+
+			cur = round_up(map->m_la + map->m_llen, PAGE_SIZE);
+			readahead_expand(rac, newstart, cur - newstart);
+			return;
+		}
+		end = round_up(end, PAGE_SIZE);
+	} else {
+		end = round_up(map->m_la, PAGE_SIZE);
+
+		if (!map->m_llen)
+			return;
+	}
+
+	cur = map->m_la + map->m_llen - 1;
+	while ((cur >= end) && (cur < i_size_read(inode))) {
+		pgoff_t index = cur >> PAGE_SHIFT;
+		struct page *page;
+
+		page = erofs_grab_cache_page_nowait(inode->i_mapping, index);
+		if (page) {
+			if (PageUptodate(page)) {
+				unlock_page(page);
+			} else {
+				err = z_erofs_do_read_page(f, page, pagepool);
+				if (err)
+					erofs_err(inode->i_sb,
+						  "readmore error at page %lu @ nid %llu",
+						  index, EROFS_I(inode)->nid);
+			}
+			put_page(page);
+		}
+
+		if (cur < PAGE_SIZE)
+			break;
+		cur = (index << PAGE_SHIFT) - 1;
+	}
+}
+
+static int z_erofs_read_folio(struct file *file, struct folio *folio)
+{
+	struct page *page = &folio->page;
+	struct inode *const inode = page->mapping->host;
+	struct erofs_sb_info *const sbi = EROFS_I_SB(inode);
+	struct z_erofs_decompress_frontend f = DECOMPRESS_FRONTEND_INIT(inode);
+	struct page *pagepool = NULL;
+	int err;
+
+	trace_erofs_readpage(page, false);
+	f.headoffset = (erofs_off_t)page->index << PAGE_SHIFT;
+
+	z_erofs_pcluster_readmore(&f, NULL, f.headoffset + PAGE_SIZE - 1,
+				  &pagepool, true);
+	err = z_erofs_do_read_page(&f, page, &pagepool);
+	z_erofs_pcluster_readmore(&f, NULL, 0, &pagepool, false);
+
+	(void)z_erofs_collector_end(&f);
+
+	/* if some compressed cluster ready, need submit them anyway */
+	z_erofs_runqueue(&f, &pagepool,
+			 z_erofs_get_sync_decompress_policy(sbi, 0));
+
+	if (err)
+		erofs_err(inode->i_sb, "failed to read, err [%d]", err);
+
+	erofs_put_metabuf(&f.map.buf);
+	erofs_release_pages(&pagepool);
+	return err;
+}
+
+static void z_erofs_readahead(struct readahead_control *rac)
+{
+	struct inode *const inode = rac->mapping->host;
+	struct erofs_sb_info *const sbi = EROFS_I_SB(inode);
+	struct z_erofs_decompress_frontend f = DECOMPRESS_FRONTEND_INIT(inode);
+	struct page *pagepool = NULL, *head = NULL, *page;
+	unsigned int nr_pages;
+
+	f.readahead = true;
+	f.headoffset = readahead_pos(rac);
+
+	z_erofs_pcluster_readmore(&f, rac, f.headoffset +
+				  readahead_length(rac) - 1, &pagepool, true);
+	nr_pages = readahead_count(rac);
+	trace_erofs_readpages(inode, readahead_index(rac), nr_pages, false);
+
+	while ((page = readahead_page(rac))) {
+		set_page_private(page, (unsigned long)head);
+		head = page;
+	}
+
+	while (head) {
+		struct page *page = head;
+		int err;
+
+		/* traversal in reverse order */
+		head = (void *)page_private(page);
+
+		err = z_erofs_do_read_page(&f, page, &pagepool);
+		if (err)
+			erofs_err(inode->i_sb,
+				  "readahead error at page %lu @ nid %llu",
+				  page->index, EROFS_I(inode)->nid);
+		put_page(page);
+	}
+	z_erofs_pcluster_readmore(&f, rac, 0, &pagepool, false);
+	(void)z_erofs_collector_end(&f);
+
+	z_erofs_runqueue(&f, &pagepool,
+			 z_erofs_get_sync_decompress_policy(sbi, nr_pages));
+	erofs_put_metabuf(&f.map.buf);
+	erofs_release_pages(&pagepool);
+}
+
+const struct address_space_operations z_erofs_aops = {
+	.read_folio = z_erofs_read_folio,
+	.readahead = z_erofs_readahead,
+};