Adding upstream version 5.10.209.upstream/5.10.209

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

1 files changed, 1365 insertions, 0 deletions

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
new file mode 100644
index 000000000..da133950d
--- /dev/null
+++ b/fs/erofs/zdata.c
@@ -0,0 +1,1365 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2018 HUAWEI, Inc.
+ *             https://www.huawei.com/
+ * Created by Gao Xiang <gaoxiang25@huawei.com>
+ */
+#include "zdata.h"
+#include "compress.h"
+#include <linux/prefetch.h>
+
+#include <trace/events/erofs.h>
+
+/*
+ * a compressed_pages[] placeholder in order to avoid
+ * being filled with file pages for in-place decompression.
+ */
+#define PAGE_UNALLOCATED     ((void *)0x5F0E4B1D)
+
+/* how to allocate cached pages for a pcluster */
+enum z_erofs_cache_alloctype {
+	DONTALLOC,	/* don't allocate any cached pages */
+	DELAYEDALLOC,	/* delayed allocation (at the time of submitting io) */
+};
+
+/*
+ * tagged pointer with 1-bit tag for all compressed pages
+ * tag 0 - the page is just found with an extra page reference
+ */
+typedef tagptr1_t compressed_page_t;
+
+#define tag_compressed_page_justfound(page) \
+	tagptr_fold(compressed_page_t, page, 1)
+
+static struct workqueue_struct *z_erofs_workqueue __read_mostly;
+static struct kmem_cache *pcluster_cachep __read_mostly;
+
+void z_erofs_exit_zip_subsystem(void)
+{
+	destroy_workqueue(z_erofs_workqueue);
+	kmem_cache_destroy(pcluster_cachep);
+}
+
+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;
+}
+
+static void z_erofs_pcluster_init_once(void *ptr)
+{
+	struct z_erofs_pcluster *pcl = ptr;
+	struct z_erofs_collection *cl = z_erofs_primarycollection(pcl);
+	unsigned int i;
+
+	mutex_init(&cl->lock);
+	cl->nr_pages = 0;
+	cl->vcnt = 0;
+	for (i = 0; i < Z_EROFS_CLUSTER_MAX_PAGES; ++i)
+		pcl->compressed_pages[i] = NULL;
+}
+
+int __init z_erofs_init_zip_subsystem(void)
+{
+	pcluster_cachep = kmem_cache_create("erofs_compress",
+					    Z_EROFS_WORKGROUP_SIZE, 0,
+					    SLAB_RECLAIM_ACCOUNT,
+					    z_erofs_pcluster_init_once);
+	if (pcluster_cachep) {
+		if (!z_erofs_init_workqueue())
+			return 0;
+
+		kmem_cache_destroy(pcluster_cachep);
+	}
+	return -ENOMEM;
+}
+
+enum z_erofs_collectmode {
+	COLLECT_SECONDARY,
+	COLLECT_PRIMARY,
+	/*
+	 * The current collection was the tail of an exist chain, in addition
+	 * that the previous processed chained collections are all decided to
+	 * be hooked up to it.
+	 * A new chain will be created for the remaining collections which are
+	 * not processed yet, therefore different from COLLECT_PRIMARY_FOLLOWED,
+	 * the next collection cannot reuse the whole page safely in
+	 * the following scenario:
+	 *  ________________________________________________________________
+	 * |      tail (partial) page     |       head (partial) page       |
+	 * |   (belongs to the next cl)   |   (belongs to the current cl)   |
+	 * |_______PRIMARY_FOLLOWED_______|________PRIMARY_HOOKED___________|
+	 */
+	COLLECT_PRIMARY_HOOKED,
+	COLLECT_PRIMARY_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)      |
+	 * |  PRIMARY_FOLLOWED or |                                        |
+	 * |_____PRIMARY_HOOKED___|____________PRIMARY_FOLLOWED____________|
+	 *
+	 * [  (*) the above page can be used as inplace I/O.               ]
+	 */
+	COLLECT_PRIMARY_FOLLOWED,
+};
+
+struct z_erofs_collector {
+	struct z_erofs_pagevec_ctor vector;
+
+	struct z_erofs_pcluster *pcl, *tailpcl;
+	struct z_erofs_collection *cl;
+	struct page **compressedpages;
+	z_erofs_next_pcluster_t owned_head;
+
+	enum z_erofs_collectmode mode;
+};
+
+struct z_erofs_decompress_frontend {
+	struct inode *const inode;
+
+	struct z_erofs_collector clt;
+	struct erofs_map_blocks map;
+
+	bool readahead;
+	/* used for applying cache strategy on the fly */
+	bool backmost;
+	erofs_off_t headoffset;
+};
+
+#define COLLECTOR_INIT() { \
+	.owned_head = Z_EROFS_PCLUSTER_TAIL, \
+	.mode = COLLECT_PRIMARY_FOLLOWED }
+
+#define DECOMPRESS_FRONTEND_INIT(__i) { \
+	.inode = __i, .clt = COLLECTOR_INIT(), \
+	.backmost = true, }
+
+static struct page *z_pagemap_global[Z_EROFS_VMAP_GLOBAL_PAGES];
+static DEFINE_MUTEX(z_pagemap_global_lock);
+
+static void preload_compressed_pages(struct z_erofs_collector *clt,
+				     struct address_space *mc,
+				     enum z_erofs_cache_alloctype type)
+{
+	const struct z_erofs_pcluster *pcl = clt->pcl;
+	const unsigned int clusterpages = BIT(pcl->clusterbits);
+	struct page **pages = clt->compressedpages;
+	pgoff_t index = pcl->obj.index + (pages - pcl->compressed_pages);
+	bool standalone = true;
+
+	if (clt->mode < COLLECT_PRIMARY_FOLLOWED)
+		return;
+
+	for (; pages < pcl->compressed_pages + clusterpages; ++pages) {
+		struct page *page;
+		compressed_page_t t;
+
+		/* the compressed page was loaded before */
+		if (READ_ONCE(*pages))
+			continue;
+
+		page = find_get_page(mc, index);
+
+		if (page) {
+			t = tag_compressed_page_justfound(page);
+		} else if (type == DELAYEDALLOC) {
+			t = tagptr_init(compressed_page_t, PAGE_UNALLOCATED);
+		} else {	/* DONTALLOC */
+			if (standalone)
+				clt->compressedpages = pages;
+			standalone = false;
+			continue;
+		}
+
+		if (!cmpxchg_relaxed(pages, NULL, tagptr_cast_ptr(t)))
+			continue;
+
+		if (page)
+			put_page(page);
+	}
+
+	if (standalone)		/* downgrade to PRIMARY_FOLLOWED_NOINPLACE */
+		clt->mode = COLLECT_PRIMARY_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);
+	struct address_space *const mapping = MNGD_MAPPING(sbi);
+	const unsigned int clusterpages = BIT(pcl->clusterbits);
+	int i;
+
+	/*
+	 * refcount of workgroup is now freezed as 1,
+	 * therefore no need to worry about available decompression users.
+	 */
+	for (i = 0; i < clusterpages; ++i) {
+		struct page *page = pcl->compressed_pages[i];
+
+		if (!page)
+			continue;
+
+		/* block other users from reclaiming or migrating the page */
+		if (!trylock_page(page))
+			return -EBUSY;
+
+		if (page->mapping != mapping)
+			continue;
+
+		/* barrier is implied in the following 'unlock_page' */
+		WRITE_ONCE(pcl->compressed_pages[i], NULL);
+		set_page_private(page, 0);
+		ClearPagePrivate(page);
+
+		unlock_page(page);
+		put_page(page);
+	}
+	return 0;
+}
+
+int erofs_try_to_free_cached_page(struct address_space *mapping,
+				  struct page *page)
+{
+	struct z_erofs_pcluster *const pcl = (void *)page_private(page);
+	const unsigned int clusterpages = BIT(pcl->clusterbits);
+	int ret = 0;	/* 0 - busy */
+
+	if (erofs_workgroup_try_to_freeze(&pcl->obj, 1)) {
+		unsigned int i;
+
+		for (i = 0; i < clusterpages; ++i) {
+			if (pcl->compressed_pages[i] == page) {
+				WRITE_ONCE(pcl->compressed_pages[i], NULL);
+				ret = 1;
+				break;
+			}
+		}
+		erofs_workgroup_unfreeze(&pcl->obj, 1);
+
+		if (ret) {
+			ClearPagePrivate(page);
+			put_page(page);
+		}
+	}
+	return ret;
+}
+
+/* page_type must be Z_EROFS_PAGE_TYPE_EXCLUSIVE */
+static inline bool z_erofs_try_inplace_io(struct z_erofs_collector *clt,
+					  struct page *page)
+{
+	struct z_erofs_pcluster *const pcl = clt->pcl;
+	const unsigned int clusterpages = BIT(pcl->clusterbits);
+
+	while (clt->compressedpages < pcl->compressed_pages + clusterpages) {
+		if (!cmpxchg(clt->compressedpages++, NULL, page))
+			return true;
+	}
+	return false;
+}
+
+/* callers must be with collection lock held */
+static int z_erofs_attach_page(struct z_erofs_collector *clt,
+			       struct page *page, enum z_erofs_page_type type,
+			       bool pvec_safereuse)
+{
+	int ret;
+
+	/* give priority for inplaceio */
+	if (clt->mode >= COLLECT_PRIMARY &&
+	    type == Z_EROFS_PAGE_TYPE_EXCLUSIVE &&
+	    z_erofs_try_inplace_io(clt, page))
+		return 0;
+
+	ret = z_erofs_pagevec_enqueue(&clt->vector, page, type,
+				      pvec_safereuse);
+	clt->cl->vcnt += (unsigned int)ret;
+	return ret ? 0 : -EAGAIN;
+}
+
+static enum z_erofs_collectmode
+try_to_claim_pcluster(struct z_erofs_pcluster *pcl,
+		      z_erofs_next_pcluster_t *owned_head)
+{
+	/* let's claim these following types of pclusters */
+retry:
+	if (pcl->next == Z_EROFS_PCLUSTER_NIL) {
+		/* type 1, nil pcluster */
+		if (cmpxchg(&pcl->next, Z_EROFS_PCLUSTER_NIL,
+			    *owned_head) != Z_EROFS_PCLUSTER_NIL)
+			goto retry;
+
+		*owned_head = &pcl->next;
+		/* lucky, I am the followee :) */
+		return COLLECT_PRIMARY_FOLLOWED;
+	} else if (pcl->next == Z_EROFS_PCLUSTER_TAIL) {
+		/*
+		 * type 2, link to the end of a existing open chain,
+		 * be careful that its submission itself is governed
+		 * by the original owned chain.
+		 */
+		if (cmpxchg(&pcl->next, Z_EROFS_PCLUSTER_TAIL,
+			    *owned_head) != Z_EROFS_PCLUSTER_TAIL)
+			goto retry;
+		*owned_head = Z_EROFS_PCLUSTER_TAIL;
+		return COLLECT_PRIMARY_HOOKED;
+	}
+	return COLLECT_PRIMARY;	/* :( better luck next time */
+}
+
+static int z_erofs_lookup_collection(struct z_erofs_collector *clt,
+				     struct inode *inode,
+				     struct erofs_map_blocks *map)
+{
+	struct z_erofs_pcluster *pcl = clt->pcl;
+	struct z_erofs_collection *cl;
+	unsigned int length;
+
+	/* to avoid unexpected loop formed by corrupted images */
+	if (clt->owned_head == &pcl->next || pcl == clt->tailpcl) {
+		DBG_BUGON(1);
+		return -EFSCORRUPTED;
+	}
+
+	cl = z_erofs_primarycollection(pcl);
+	if (cl->pageofs != (map->m_la & ~PAGE_MASK)) {
+		DBG_BUGON(1);
+		return -EFSCORRUPTED;
+	}
+
+	length = READ_ONCE(pcl->length);
+	if (length & Z_EROFS_PCLUSTER_FULL_LENGTH) {
+		if ((map->m_llen << Z_EROFS_PCLUSTER_LENGTH_BIT) > length) {
+			DBG_BUGON(1);
+			return -EFSCORRUPTED;
+		}
+	} else {
+		unsigned int llen = map->m_llen << Z_EROFS_PCLUSTER_LENGTH_BIT;
+
+		if (map->m_flags & EROFS_MAP_FULL_MAPPED)
+			llen |= Z_EROFS_PCLUSTER_FULL_LENGTH;
+
+		while (llen > length &&
+		       length != cmpxchg_relaxed(&pcl->length, length, llen)) {
+			cpu_relax();
+			length = READ_ONCE(pcl->length);
+		}
+	}
+	mutex_lock(&cl->lock);
+	/* used to check tail merging loop due to corrupted images */
+	if (clt->owned_head == Z_EROFS_PCLUSTER_TAIL)
+		clt->tailpcl = pcl;
+	clt->mode = try_to_claim_pcluster(pcl, &clt->owned_head);
+	/* clean tailpcl if the current owned_head is Z_EROFS_PCLUSTER_TAIL */
+	if (clt->owned_head == Z_EROFS_PCLUSTER_TAIL)
+		clt->tailpcl = NULL;
+	clt->cl = cl;
+	return 0;
+}
+
+static int z_erofs_register_collection(struct z_erofs_collector *clt,
+				       struct inode *inode,
+				       struct erofs_map_blocks *map)
+{
+	struct z_erofs_pcluster *pcl;
+	struct z_erofs_collection *cl;
+	struct erofs_workgroup *grp;
+	int err;
+
+	/* no available workgroup, let's allocate one */
+	pcl = kmem_cache_alloc(pcluster_cachep, GFP_NOFS);
+	if (!pcl)
+		return -ENOMEM;
+
+	atomic_set(&pcl->obj.refcount, 1);
+	pcl->obj.index = map->m_pa >> PAGE_SHIFT;
+
+	pcl->length = (map->m_llen << Z_EROFS_PCLUSTER_LENGTH_BIT) |
+		(map->m_flags & EROFS_MAP_FULL_MAPPED ?
+			Z_EROFS_PCLUSTER_FULL_LENGTH : 0);
+
+	if (map->m_flags & EROFS_MAP_ZIPPED)
+		pcl->algorithmformat = Z_EROFS_COMPRESSION_LZ4;
+	else
+		pcl->algorithmformat = Z_EROFS_COMPRESSION_SHIFTED;
+
+	pcl->clusterbits = EROFS_I(inode)->z_physical_clusterbits[0];
+	pcl->clusterbits -= PAGE_SHIFT;
+
+	/* new pclusters should be claimed as type 1, primary and followed */
+	pcl->next = clt->owned_head;
+	clt->mode = COLLECT_PRIMARY_FOLLOWED;
+
+	cl = z_erofs_primarycollection(pcl);
+
+	/* must be cleaned before freeing to slab */
+	DBG_BUGON(cl->nr_pages);
+	DBG_BUGON(cl->vcnt);
+
+	cl->pageofs = map->m_la & ~PAGE_MASK;
+
+	/*
+	 * lock all primary followed works before visible to others
+	 * and mutex_trylock *never* fails for a new pcluster.
+	 */
+	DBG_BUGON(!mutex_trylock(&cl->lock));
+
+	grp = erofs_insert_workgroup(inode->i_sb, &pcl->obj);
+	if (IS_ERR(grp)) {
+		err = PTR_ERR(grp);
+		goto err_out;
+	}
+
+	if (grp != &pcl->obj) {
+		clt->pcl = container_of(grp, struct z_erofs_pcluster, obj);
+		err = -EEXIST;
+		goto err_out;
+	}
+	/* used to check tail merging loop due to corrupted images */
+	if (clt->owned_head == Z_EROFS_PCLUSTER_TAIL)
+		clt->tailpcl = pcl;
+	clt->owned_head = &pcl->next;
+	clt->pcl = pcl;
+	clt->cl = cl;
+	return 0;
+
+err_out:
+	mutex_unlock(&cl->lock);
+	kmem_cache_free(pcluster_cachep, pcl);
+	return err;
+}
+
+static int z_erofs_collector_begin(struct z_erofs_collector *clt,
+				   struct inode *inode,
+				   struct erofs_map_blocks *map)
+{
+	struct erofs_workgroup *grp;
+	int ret;
+
+	DBG_BUGON(clt->cl);
+
+	/* must be Z_EROFS_PCLUSTER_TAIL or pointed to previous collection */
+	DBG_BUGON(clt->owned_head == Z_EROFS_PCLUSTER_NIL);
+	DBG_BUGON(clt->owned_head == Z_EROFS_PCLUSTER_TAIL_CLOSED);
+
+	if (!PAGE_ALIGNED(map->m_pa)) {
+		DBG_BUGON(1);
+		return -EINVAL;
+	}
+
+	grp = erofs_find_workgroup(inode->i_sb, map->m_pa >> PAGE_SHIFT);
+	if (grp) {
+		clt->pcl = container_of(grp, struct z_erofs_pcluster, obj);
+	} else {
+		ret = z_erofs_register_collection(clt, inode, map);
+
+		if (!ret)
+			goto out;
+		if (ret != -EEXIST)
+			return ret;
+	}
+
+	ret = z_erofs_lookup_collection(clt, inode, map);
+	if (ret) {
+		erofs_workgroup_put(&clt->pcl->obj);
+		return ret;
+	}
+
+out:
+	z_erofs_pagevec_ctor_init(&clt->vector, Z_EROFS_NR_INLINE_PAGEVECS,
+				  clt->cl->pagevec, clt->cl->vcnt);
+
+	clt->compressedpages = clt->pcl->compressed_pages;
+	if (clt->mode <= COLLECT_PRIMARY) /* cannot do in-place I/O */
+		clt->compressedpages += Z_EROFS_CLUSTER_MAX_PAGES;
+	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)
+{
+	struct z_erofs_collection *const cl =
+		container_of(head, struct z_erofs_collection, rcu);
+
+	kmem_cache_free(pcluster_cachep,
+			container_of(cl, struct z_erofs_pcluster,
+				     primary_collection));
+}
+
+void erofs_workgroup_free_rcu(struct erofs_workgroup *grp)
+{
+	struct z_erofs_pcluster *const pcl =
+		container_of(grp, struct z_erofs_pcluster, obj);
+	struct z_erofs_collection *const cl = z_erofs_primarycollection(pcl);
+
+	call_rcu(&cl->rcu, z_erofs_rcu_callback);
+}
+
+static void z_erofs_collection_put(struct z_erofs_collection *cl)
+{
+	struct z_erofs_pcluster *const pcl =
+		container_of(cl, struct z_erofs_pcluster, primary_collection);
+
+	erofs_workgroup_put(&pcl->obj);
+}
+
+static bool z_erofs_collector_end(struct z_erofs_collector *clt)
+{
+	struct z_erofs_collection *cl = clt->cl;
+
+	if (!cl)
+		return false;
+
+	z_erofs_pagevec_ctor_exit(&clt->vector, false);
+	mutex_unlock(&cl->lock);
+
+	/*
+	 * if all pending pages are added, don't hold its reference
+	 * any longer if the pcluster isn't hosted by ourselves.
+	 */
+	if (clt->mode < COLLECT_PRIMARY_FOLLOWED_NOINPLACE)
+		z_erofs_collection_put(cl);
+
+	clt->cl = NULL;
+	return true;
+}
+
+static bool should_alloc_managed_pages(struct z_erofs_decompress_frontend *fe,
+				       unsigned int cachestrategy,
+				       erofs_off_t la)
+{
+	if (cachestrategy <= EROFS_ZIP_CACHE_DISABLED)
+		return false;
+
+	if (fe->backmost)
+		return true;
+
+	return cachestrategy >= EROFS_ZIP_CACHE_READAROUND &&
+		la < fe->headoffset;
+}
+
+static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
+				struct page *page)
+{
+	struct inode *const inode = fe->inode;
+	struct erofs_sb_info *const sbi = EROFS_I_SB(inode);
+	struct erofs_map_blocks *const map = &fe->map;
+	struct z_erofs_collector *const clt = &fe->clt;
+	const loff_t offset = page_offset(page);
+	bool tight = true;
+
+	enum z_erofs_cache_alloctype cache_strategy;
+	enum z_erofs_page_type page_type;
+	unsigned int cur, end, spiltted, index;
+	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;
+
+	/* lucky, within the range of the current map_blocks */
+	if (offset + cur >= map->m_la &&
+	    offset + cur < map->m_la + map->m_llen) {
+		/* didn't get a valid collection previously (very rare) */
+		if (!clt->cl)
+			goto restart_now;
+		goto hitted;
+	}
+
+	/* go ahead the next map_blocks */
+	erofs_dbg("%s: [out-of-range] pos %llu", __func__, offset + cur);
+
+	if (z_erofs_collector_end(clt))
+		fe->backmost = false;
+
+	map->m_la = offset + cur;
+	map->m_llen = 0;
+	err = z_erofs_map_blocks_iter(inode, map, 0);
+	if (err)
+		goto err_out;
+
+restart_now:
+	if (!(map->m_flags & EROFS_MAP_MAPPED))
+		goto hitted;
+
+	err = z_erofs_collector_begin(clt, inode, map);
+	if (err)
+		goto err_out;
+
+	/* preload all compressed pages (maybe downgrade role if necessary) */
+	if (should_alloc_managed_pages(fe, sbi->ctx.cache_strategy, map->m_la))
+		cache_strategy = DELAYEDALLOC;
+	else
+		cache_strategy = DONTALLOC;
+
+	preload_compressed_pages(clt, MNGD_MAPPING(sbi), cache_strategy);
+
+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 pagevec (should be processed in strict order.)
+	 */
+	tight &= (clt->mode >= COLLECT_PRIMARY_HOOKED &&
+		  clt->mode != COLLECT_PRIMARY_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;
+	}
+
+	/* let's derive page type */
+	page_type = cur ? Z_EROFS_VLE_PAGE_TYPE_HEAD :
+		(!spiltted ? Z_EROFS_PAGE_TYPE_EXCLUSIVE :
+			(tight ? Z_EROFS_PAGE_TYPE_EXCLUSIVE :
+				Z_EROFS_VLE_PAGE_TYPE_TAIL_SHARED));
+
+	if (cur)
+		tight &= (clt->mode >= COLLECT_PRIMARY_FOLLOWED);
+
+retry:
+	err = z_erofs_attach_page(clt, page, page_type,
+				  clt->mode >= COLLECT_PRIMARY_FOLLOWED);
+	/* should allocate an additional staging page for pagevec */
+	if (err == -EAGAIN) {
+		struct page *const newpage =
+				alloc_page(GFP_NOFS | __GFP_NOFAIL);
+
+		newpage->mapping = Z_EROFS_MAPPING_STAGING;
+		err = z_erofs_attach_page(clt, newpage,
+					  Z_EROFS_PAGE_TYPE_EXCLUSIVE, true);
+		if (!err)
+			goto retry;
+	}
+
+	if (err)
+		goto err_out;
+
+	index = page->index - (map->m_la >> PAGE_SHIFT);
+
+	z_erofs_onlinepage_fixup(page, index, true);
+
+	/* bump up the number of spiltted parts of a page */
+	++spiltted;
+	/* also update nr_pages */
+	clt->cl->nr_pages = max_t(pgoff_t, clt->cl->nr_pages, index + 1);
+next_part:
+	/* can be used for verification */
+	map->m_llen = offset + cur - map->m_la;
+
+	end = cur;
+	if (end > 0)
+		goto repeat;
+
+out:
+	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;
+
+	/* if some error occurred while processing this page */
+err_out:
+	SetPageError(page);
+	goto out;
+}
+
+static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
+				       bool sync, int bios)
+{
+	/* wake up the caller thread for sync decompression */
+	if (sync) {
+		unsigned long flags;
+
+		spin_lock_irqsave(&io->u.wait.lock, flags);
+		if (!atomic_add_return(bios, &io->pending_bios))
+			wake_up_locked(&io->u.wait);
+		spin_unlock_irqrestore(&io->u.wait.lock, flags);
+		return;
+	}
+
+	if (!atomic_add_return(bios, &io->pending_bios))
+		queue_work(z_erofs_workqueue, &io->u.work);
+}
+
+static void z_erofs_decompressqueue_endio(struct bio *bio)
+{
+	tagptr1_t t = tagptr_init(tagptr1_t, bio->bi_private);
+	struct z_erofs_decompressqueue *q = tagptr_unfold_ptr(t);
+	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(!page->mapping);
+
+		if (err)
+			SetPageError(page);
+
+		if (erofs_page_is_managed(EROFS_SB(q->sb), page)) {
+			if (!err)
+				SetPageUptodate(page);
+			unlock_page(page);
+		}
+	}
+	z_erofs_decompress_kickoff(q, tagptr_unfold_tags(t), -1);
+	bio_put(bio);
+}
+
+static int z_erofs_decompress_pcluster(struct super_block *sb,
+				       struct z_erofs_pcluster *pcl,
+				       struct list_head *pagepool)
+{
+	struct erofs_sb_info *const sbi = EROFS_SB(sb);
+	const unsigned int clusterpages = BIT(pcl->clusterbits);
+	struct z_erofs_pagevec_ctor ctor;
+	unsigned int i, outputsize, llen, nr_pages;
+	struct page *pages_onstack[Z_EROFS_VMAP_ONSTACK_PAGES];
+	struct page **pages, **compressed_pages, *page;
+
+	enum z_erofs_page_type page_type;
+	bool overlapped, partial;
+	struct z_erofs_collection *cl;
+	int err;
+
+	might_sleep();
+	cl = z_erofs_primarycollection(pcl);
+	DBG_BUGON(!READ_ONCE(cl->nr_pages));
+
+	mutex_lock(&cl->lock);
+	nr_pages = cl->nr_pages;
+
+	if (nr_pages <= Z_EROFS_VMAP_ONSTACK_PAGES) {
+		pages = pages_onstack;
+	} else if (nr_pages <= Z_EROFS_VMAP_GLOBAL_PAGES &&
+		   mutex_trylock(&z_pagemap_global_lock)) {
+		pages = z_pagemap_global;
+	} else {
+		gfp_t gfp_flags = GFP_KERNEL;
+
+		if (nr_pages > Z_EROFS_VMAP_GLOBAL_PAGES)
+			gfp_flags |= __GFP_NOFAIL;
+
+		pages = kvmalloc_array(nr_pages, sizeof(struct page *),
+				       gfp_flags);
+
+		/* fallback to global pagemap for the lowmem scenario */
+		if (!pages) {
+			mutex_lock(&z_pagemap_global_lock);
+			pages = z_pagemap_global;
+		}
+	}
+
+	for (i = 0; i < nr_pages; ++i)
+		pages[i] = NULL;
+
+	err = 0;
+	z_erofs_pagevec_ctor_init(&ctor, Z_EROFS_NR_INLINE_PAGEVECS,
+				  cl->pagevec, 0);
+
+	for (i = 0; i < cl->vcnt; ++i) {
+		unsigned int pagenr;
+
+		page = z_erofs_pagevec_dequeue(&ctor, &page_type);
+
+		/* all pages in pagevec ought to be valid */
+		DBG_BUGON(!page);
+		DBG_BUGON(!page->mapping);
+
+		if (z_erofs_put_stagingpage(pagepool, page))
+			continue;
+
+		if (page_type == Z_EROFS_VLE_PAGE_TYPE_HEAD)
+			pagenr = 0;
+		else
+			pagenr = z_erofs_onlinepage_index(page);
+
+		DBG_BUGON(pagenr >= nr_pages);
+
+		/*
+		 * currently EROFS doesn't support multiref(dedup),
+		 * so here erroring out one multiref page.
+		 */
+		if (pages[pagenr]) {
+			DBG_BUGON(1);
+			SetPageError(pages[pagenr]);
+			z_erofs_onlinepage_endio(pages[pagenr]);
+			err = -EFSCORRUPTED;
+		}
+		pages[pagenr] = page;
+	}
+	z_erofs_pagevec_ctor_exit(&ctor, true);
+
+	overlapped = false;
+	compressed_pages = pcl->compressed_pages;
+
+	for (i = 0; i < clusterpages; ++i) {
+		unsigned int pagenr;
+
+		page = compressed_pages[i];
+
+		/* all compressed pages ought to be valid */
+		DBG_BUGON(!page);
+		DBG_BUGON(!page->mapping);
+
+		if (!z_erofs_page_is_staging(page)) {
+			if (erofs_page_is_managed(sbi, page)) {
+				if (!PageUptodate(page))
+					err = -EIO;
+				continue;
+			}
+
+			/*
+			 * only if non-head page can be selected
+			 * for inplace decompression
+			 */
+			pagenr = z_erofs_onlinepage_index(page);
+
+			DBG_BUGON(pagenr >= nr_pages);
+			if (pages[pagenr]) {
+				DBG_BUGON(1);
+				SetPageError(pages[pagenr]);
+				z_erofs_onlinepage_endio(pages[pagenr]);
+				err = -EFSCORRUPTED;
+			}
+			pages[pagenr] = page;
+
+			overlapped = true;
+		}
+
+		/* PG_error needs checking for inplaced and staging pages */
+		if (PageError(page)) {
+			DBG_BUGON(PageUptodate(page));
+			err = -EIO;
+		}
+	}
+
+	if (err)
+		goto out;
+
+	llen = pcl->length >> Z_EROFS_PCLUSTER_LENGTH_BIT;
+	if (nr_pages << PAGE_SHIFT >= cl->pageofs + llen) {
+		outputsize = llen;
+		partial = !(pcl->length & Z_EROFS_PCLUSTER_FULL_LENGTH);
+	} else {
+		outputsize = (nr_pages << PAGE_SHIFT) - cl->pageofs;
+		partial = true;
+	}
+
+	err = z_erofs_decompress(&(struct z_erofs_decompress_req) {
+					.sb = sb,
+					.in = compressed_pages,
+					.out = pages,
+					.pageofs_out = cl->pageofs,
+					.inputsize = PAGE_SIZE,
+					.outputsize = outputsize,
+					.alg = pcl->algorithmformat,
+					.inplace_io = overlapped,
+					.partial_decoding = partial
+				 }, pagepool);
+
+out:
+	/* must handle all compressed pages before endding pages */
+	for (i = 0; i < clusterpages; ++i) {
+		page = compressed_pages[i];
+
+		if (erofs_page_is_managed(sbi, page))
+			continue;
+
+		/* recycle all individual staging pages */
+		(void)z_erofs_put_stagingpage(pagepool, page);
+
+		WRITE_ONCE(compressed_pages[i], NULL);
+	}
+
+	for (i = 0; i < nr_pages; ++i) {
+		page = pages[i];
+		if (!page)
+			continue;
+
+		DBG_BUGON(!page->mapping);
+
+		/* recycle all individual staging pages */
+		if (z_erofs_put_stagingpage(pagepool, page))
+			continue;
+
+		if (err < 0)
+			SetPageError(page);
+
+		z_erofs_onlinepage_endio(page);
+	}
+
+	if (pages == z_pagemap_global)
+		mutex_unlock(&z_pagemap_global_lock);
+	else if (pages != pages_onstack)
+		kvfree(pages);
+
+	cl->nr_pages = 0;
+	cl->vcnt = 0;
+
+	/* all cl locks MUST be taken before the following line */
+	WRITE_ONCE(pcl->next, Z_EROFS_PCLUSTER_NIL);
+
+	/* all cl locks SHOULD be released right now */
+	mutex_unlock(&cl->lock);
+
+	z_erofs_collection_put(cl);
+	return err;
+}
+
+static void z_erofs_decompress_queue(const struct z_erofs_decompressqueue *io,
+				     struct list_head *pagepool)
+{
+	z_erofs_next_pcluster_t owned = io->head;
+
+	while (owned != Z_EROFS_PCLUSTER_TAIL_CLOSED) {
+		struct z_erofs_pcluster *pcl;
+
+		/* no possible that 'owned' equals Z_EROFS_WORK_TPTR_TAIL */
+		DBG_BUGON(owned == Z_EROFS_PCLUSTER_TAIL);
+
+		/* no possible that 'owned' equals NULL */
+		DBG_BUGON(owned == Z_EROFS_PCLUSTER_NIL);
+
+		pcl = container_of(owned, struct z_erofs_pcluster, next);
+		owned = READ_ONCE(pcl->next);
+
+		z_erofs_decompress_pcluster(io->sb, pcl, pagepool);
+	}
+}
+
+static void z_erofs_decompressqueue_work(struct work_struct *work)
+{
+	struct z_erofs_decompressqueue *bgq =
+		container_of(work, struct z_erofs_decompressqueue, u.work);
+	LIST_HEAD(pagepool);
+
+	DBG_BUGON(bgq->head == Z_EROFS_PCLUSTER_TAIL_CLOSED);
+	z_erofs_decompress_queue(bgq, &pagepool);
+
+	put_pages_list(&pagepool);
+	kvfree(bgq);
+}
+
+static struct page *pickup_page_for_submission(struct z_erofs_pcluster *pcl,
+					       unsigned int nr,
+					       struct list_head *pagepool,
+					       struct address_space *mc,
+					       gfp_t gfp)
+{
+	const pgoff_t index = pcl->obj.index;
+	bool tocache = false;
+
+	struct address_space *mapping;
+	struct page *oldpage, *page;
+
+	compressed_page_t t;
+	int justfound;
+
+repeat:
+	page = READ_ONCE(pcl->compressed_pages[nr]);
+	oldpage = page;
+
+	if (!page)
+		goto out_allocpage;
+
+	/*
+	 * the cached page has not been allocated and
+	 * an placeholder is out there, prepare it now.
+	 */
+	if (page == PAGE_UNALLOCATED) {
+		tocache = true;
+		goto out_allocpage;
+	}
+
+	/* process the target tagged pointer */
+	t = tagptr_init(compressed_page_t, page);
+	justfound = tagptr_unfold_tags(t);
+	page = tagptr_unfold_ptr(t);
+
+	mapping = READ_ONCE(page->mapping);
+
+	/*
+	 * unmanaged (file) pages are all locked solidly,
+	 * therefore it is impossible for `mapping' to be NULL.
+	 */
+	if (mapping && mapping != mc)
+		/* ought to be unmanaged pages */
+		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_pages[nr], page);
+
+		ClearPageError(page);
+		if (!PagePrivate(page)) {
+			/*
+			 * impossible to be !PagePrivate(page) for
+			 * the current restriction as well if
+			 * the page is already in compressed_pages[].
+			 */
+			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 (!tocache || add_to_page_cache_lru(page, mc, index + nr, gfp)) {
+		/* non-LRU / non-movable temporary page is needed */
+		page->mapping = Z_EROFS_MAPPING_STAGING;
+		tocache = false;
+	}
+
+	if (oldpage != cmpxchg(&pcl->compressed_pages[nr], oldpage, page)) {
+		if (tocache) {
+			/* since it added to managed cache successfully */
+			unlock_page(page);
+			put_page(page);
+		} else {
+			list_add(&page->lru, pagepool);
+		}
+		cond_resched();
+		goto repeat;
+	}
+
+	if (tocache) {
+		set_page_private(page, (unsigned long)pcl);
+		SetPagePrivate(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_waitqueue_head(&fgq->u.wait);
+		atomic_set(&fgq->pending_bios, 0);
+	}
+	q->sb = sb;
+	q->head = Z_EROFS_PCLUSTER_TAIL_CLOSED;
+	return q;
+}
+
+/* define decompression jobqueue types */
+enum {
+	JQ_BYPASS,
+	JQ_SUBMIT,
+	NR_JOBQUEUES,
+};
+
+static void *jobqueueset_init(struct super_block *sb,
+			      struct z_erofs_decompressqueue *q[],
+			      struct z_erofs_decompressqueue *fgq, bool *fg)
+{
+	/*
+	 * 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, fg);
+
+	return tagptr_cast_ptr(tagptr_fold(tagptr1_t, q[JQ_SUBMIT], *fg));
+}
+
+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];
+
+	DBG_BUGON(owned_head == Z_EROFS_PCLUSTER_TAIL_CLOSED);
+	if (owned_head == Z_EROFS_PCLUSTER_TAIL)
+		owned_head = Z_EROFS_PCLUSTER_TAIL_CLOSED;
+
+	WRITE_ONCE(pcl->next, Z_EROFS_PCLUSTER_TAIL_CLOSED);
+
+	WRITE_ONCE(*submit_qtail, owned_head);
+	WRITE_ONCE(*bypass_qtail, &pcl->next);
+
+	qtail[JQ_BYPASS] = &pcl->next;
+}
+
+static void z_erofs_submit_queue(struct super_block *sb,
+				 struct z_erofs_decompress_frontend *f,
+				 struct list_head *pagepool,
+				 struct z_erofs_decompressqueue *fgq,
+				 bool *force_fg)
+{
+	struct erofs_sb_info *const sbi = EROFS_SB(sb);
+	z_erofs_next_pcluster_t qtail[NR_JOBQUEUES];
+	struct z_erofs_decompressqueue *q[NR_JOBQUEUES];
+	void *bi_private;
+	z_erofs_next_pcluster_t owned_head = f->clt.owned_head;
+	/* since bio will be NULL, no need to initialize last_index */
+	pgoff_t last_index;
+	unsigned int nr_bios = 0;
+	struct bio *bio = NULL;
+
+	bi_private = jobqueueset_init(sb, q, fgq, 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 z_erofs_pcluster *pcl;
+		pgoff_t cur, end;
+		unsigned int i = 0;
+		bool bypass = true;
+
+		/* no possible 'owned_head' equals the following */
+		DBG_BUGON(owned_head == Z_EROFS_PCLUSTER_TAIL_CLOSED);
+		DBG_BUGON(owned_head == Z_EROFS_PCLUSTER_NIL);
+
+		pcl = container_of(owned_head, struct z_erofs_pcluster, next);
+
+		cur = pcl->obj.index;
+		end = cur + BIT(pcl->clusterbits);
+
+		/* close the main owned chain at first */
+		owned_head = cmpxchg(&pcl->next, Z_EROFS_PCLUSTER_TAIL,
+				     Z_EROFS_PCLUSTER_TAIL_CLOSED);
+
+		do {
+			struct page *page;
+
+			page = pickup_page_for_submission(pcl, i++, pagepool,
+							  MNGD_MAPPING(sbi),
+							  GFP_NOFS);
+			if (!page)
+				continue;
+
+			if (bio && cur != last_index + 1) {
+submit_bio_retry:
+				submit_bio(bio);
+				bio = NULL;
+			}
+
+			if (!bio) {
+				bio = bio_alloc(GFP_NOIO, BIO_MAX_PAGES);
+
+				bio->bi_end_io = z_erofs_decompressqueue_endio;
+				bio_set_dev(bio, sb->s_bdev);
+				bio->bi_iter.bi_sector = (sector_t)cur <<
+					LOG_SECTORS_PER_BLOCK;
+				bio->bi_private = bi_private;
+				bio->bi_opf = REQ_OP_READ;
+				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);
+
+	/*
+	 * 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], *force_fg, nr_bios);
+}
+
+static void z_erofs_runqueue(struct super_block *sb,
+			     struct z_erofs_decompress_frontend *f,
+			     struct list_head *pagepool, bool force_fg)
+{
+	struct z_erofs_decompressqueue io[NR_JOBQUEUES];
+
+	if (f->clt.owned_head == Z_EROFS_PCLUSTER_TAIL)
+		return;
+	z_erofs_submit_queue(sb, 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 */
+	io_wait_event(io[JQ_SUBMIT].u.wait,
+		      !atomic_read(&io[JQ_SUBMIT].pending_bios));
+
+	/* handle synchronous decompress queue in the caller context */
+	z_erofs_decompress_queue(&io[JQ_SUBMIT], pagepool);
+}
+
+static int z_erofs_readpage(struct file *file, struct page *page)
+{
+	struct inode *const inode = page->mapping->host;
+	struct z_erofs_decompress_frontend f = DECOMPRESS_FRONTEND_INIT(inode);
+	int err;
+	LIST_HEAD(pagepool);
+
+	trace_erofs_readpage(page, false);
+
+	f.headoffset = (erofs_off_t)page->index << PAGE_SHIFT;
+
+	err = z_erofs_do_read_page(&f, page);
+	(void)z_erofs_collector_end(&f.clt);
+
+	/* if some compressed cluster ready, need submit them anyway */
+	z_erofs_runqueue(inode->i_sb, &f, &pagepool, true);
+
+	if (err)
+		erofs_err(inode->i_sb, "failed to read, err [%d]", err);
+
+	if (f.map.mpage)
+		put_page(f.map.mpage);
+
+	/* clean up the remaining free pages */
+	put_pages_list(&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);
+
+	unsigned int nr_pages = readahead_count(rac);
+	bool sync = (nr_pages <= sbi->ctx.max_sync_decompress_pages);
+	struct z_erofs_decompress_frontend f = DECOMPRESS_FRONTEND_INIT(inode);
+	struct page *page, *head = NULL;
+	LIST_HEAD(pagepool);
+
+	trace_erofs_readpages(inode, readahead_index(rac), nr_pages, false);
+
+	f.readahead = true;
+	f.headoffset = readahead_pos(rac);
+
+	while ((page = readahead_page(rac))) {
+		prefetchw(&page->flags);
+
+		/*
+		 * A pure asynchronous readahead is indicated if
+		 * a PG_readahead marked page is hitted at first.
+		 * Let's also do asynchronous decompression for this case.
+		 */
+		sync &= !(PageReadahead(page) && !head);
+
+		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);
+		if (err)
+			erofs_err(inode->i_sb,
+				  "readahead error at page %lu @ nid %llu",
+				  page->index, EROFS_I(inode)->nid);
+		put_page(page);
+	}
+
+	(void)z_erofs_collector_end(&f.clt);
+
+	z_erofs_runqueue(inode->i_sb, &f, &pagepool, sync);
+
+	if (f.map.mpage)
+		put_page(f.map.mpage);
+
+	/* clean up the remaining free pages */
+	put_pages_list(&pagepool);
+}
+
+const struct address_space_operations z_erofs_aops = {
+	.readpage = z_erofs_readpage,
+	.readahead = z_erofs_readahead,
+};
+