Adding upstream version 5.10.209.upstream/5.10.209

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

1 files changed, 1366 insertions, 0 deletions

diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
new file mode 100644
index 000000000..2739e218d
--- /dev/null
+++ b/fs/fuse/dax.c
@@ -0,0 +1,1366 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * dax: direct host memory access
+ * Copyright (C) 2020 Red Hat, Inc.
+ */
+
+#include "fuse_i.h"
+
+#include <linux/delay.h>
+#include <linux/dax.h>
+#include <linux/uio.h>
+#include <linux/pfn_t.h>
+#include <linux/iomap.h>
+#include <linux/interval_tree.h>
+
+/*
+ * Default memory range size.  A power of 2 so it agrees with common FUSE_INIT
+ * map_alignment values 4KB and 64KB.
+ */
+#define FUSE_DAX_SHIFT	21
+#define FUSE_DAX_SZ	(1 << FUSE_DAX_SHIFT)
+#define FUSE_DAX_PAGES	(FUSE_DAX_SZ / PAGE_SIZE)
+
+/* Number of ranges reclaimer will try to free in one invocation */
+#define FUSE_DAX_RECLAIM_CHUNK		(10)
+
+/*
+ * Dax memory reclaim threshold in percetage of total ranges. When free
+ * number of free ranges drops below this threshold, reclaim can trigger
+ * Default is 20%
+ */
+#define FUSE_DAX_RECLAIM_THRESHOLD	(20)
+
+/** Translation information for file offsets to DAX window offsets */
+struct fuse_dax_mapping {
+	/* Pointer to inode where this memory range is mapped */
+	struct inode *inode;
+
+	/* Will connect in fcd->free_ranges to keep track of free memory */
+	struct list_head list;
+
+	/* For interval tree in file/inode */
+	struct interval_tree_node itn;
+
+	/* Will connect in fc->busy_ranges to keep track busy memory */
+	struct list_head busy_list;
+
+	/** Position in DAX window */
+	u64 window_offset;
+
+	/** Length of mapping, in bytes */
+	loff_t length;
+
+	/* Is this mapping read-only or read-write */
+	bool writable;
+
+	/* reference count when the mapping is used by dax iomap. */
+	refcount_t refcnt;
+};
+
+/* Per-inode dax map */
+struct fuse_inode_dax {
+	/* Semaphore to protect modifications to the dmap tree */
+	struct rw_semaphore sem;
+
+	/* Sorted rb tree of struct fuse_dax_mapping elements */
+	struct rb_root_cached tree;
+	unsigned long nr;
+};
+
+struct fuse_conn_dax {
+	/* DAX device */
+	struct dax_device *dev;
+
+	/* Lock protecting accessess to  members of this structure */
+	spinlock_t lock;
+
+	/* List of memory ranges which are busy */
+	unsigned long nr_busy_ranges;
+	struct list_head busy_ranges;
+
+	/* Worker to free up memory ranges */
+	struct delayed_work free_work;
+
+	/* Wait queue for a dax range to become free */
+	wait_queue_head_t range_waitq;
+
+	/* DAX Window Free Ranges */
+	long nr_free_ranges;
+	struct list_head free_ranges;
+
+	unsigned long nr_ranges;
+};
+
+static inline struct fuse_dax_mapping *
+node_to_dmap(struct interval_tree_node *node)
+{
+	if (!node)
+		return NULL;
+
+	return container_of(node, struct fuse_dax_mapping, itn);
+}
+
+static struct fuse_dax_mapping *
+alloc_dax_mapping_reclaim(struct fuse_conn_dax *fcd, struct inode *inode);
+
+static void
+__kick_dmap_free_worker(struct fuse_conn_dax *fcd, unsigned long delay_ms)
+{
+	unsigned long free_threshold;
+
+	/* If number of free ranges are below threshold, start reclaim */
+	free_threshold = max_t(unsigned long, fcd->nr_ranges * FUSE_DAX_RECLAIM_THRESHOLD / 100,
+			     1);
+	if (fcd->nr_free_ranges < free_threshold)
+		queue_delayed_work(system_long_wq, &fcd->free_work,
+				   msecs_to_jiffies(delay_ms));
+}
+
+static void kick_dmap_free_worker(struct fuse_conn_dax *fcd,
+				  unsigned long delay_ms)
+{
+	spin_lock(&fcd->lock);
+	__kick_dmap_free_worker(fcd, delay_ms);
+	spin_unlock(&fcd->lock);
+}
+
+static struct fuse_dax_mapping *alloc_dax_mapping(struct fuse_conn_dax *fcd)
+{
+	struct fuse_dax_mapping *dmap;
+
+	spin_lock(&fcd->lock);
+	dmap = list_first_entry_or_null(&fcd->free_ranges,
+					struct fuse_dax_mapping, list);
+	if (dmap) {
+		list_del_init(&dmap->list);
+		WARN_ON(fcd->nr_free_ranges <= 0);
+		fcd->nr_free_ranges--;
+	}
+	spin_unlock(&fcd->lock);
+
+	kick_dmap_free_worker(fcd, 0);
+	return dmap;
+}
+
+/* This assumes fcd->lock is held */
+static void __dmap_remove_busy_list(struct fuse_conn_dax *fcd,
+				    struct fuse_dax_mapping *dmap)
+{
+	list_del_init(&dmap->busy_list);
+	WARN_ON(fcd->nr_busy_ranges == 0);
+	fcd->nr_busy_ranges--;
+}
+
+static void dmap_remove_busy_list(struct fuse_conn_dax *fcd,
+				  struct fuse_dax_mapping *dmap)
+{
+	spin_lock(&fcd->lock);
+	__dmap_remove_busy_list(fcd, dmap);
+	spin_unlock(&fcd->lock);
+}
+
+/* This assumes fcd->lock is held */
+static void __dmap_add_to_free_pool(struct fuse_conn_dax *fcd,
+				struct fuse_dax_mapping *dmap)
+{
+	list_add_tail(&dmap->list, &fcd->free_ranges);
+	fcd->nr_free_ranges++;
+	wake_up(&fcd->range_waitq);
+}
+
+static void dmap_add_to_free_pool(struct fuse_conn_dax *fcd,
+				struct fuse_dax_mapping *dmap)
+{
+	/* Return fuse_dax_mapping to free list */
+	spin_lock(&fcd->lock);
+	__dmap_add_to_free_pool(fcd, dmap);
+	spin_unlock(&fcd->lock);
+}
+
+static int fuse_setup_one_mapping(struct inode *inode, unsigned long start_idx,
+				  struct fuse_dax_mapping *dmap, bool writable,
+				  bool upgrade)
+{
+	struct fuse_mount *fm = get_fuse_mount(inode);
+	struct fuse_conn_dax *fcd = fm->fc->dax;
+	struct fuse_inode *fi = get_fuse_inode(inode);
+	struct fuse_setupmapping_in inarg;
+	loff_t offset = start_idx << FUSE_DAX_SHIFT;
+	FUSE_ARGS(args);
+	ssize_t err;
+
+	WARN_ON(fcd->nr_free_ranges < 0);
+
+	/* Ask fuse daemon to setup mapping */
+	memset(&inarg, 0, sizeof(inarg));
+	inarg.foffset = offset;
+	inarg.fh = -1;
+	inarg.moffset = dmap->window_offset;
+	inarg.len = FUSE_DAX_SZ;
+	inarg.flags |= FUSE_SETUPMAPPING_FLAG_READ;
+	if (writable)
+		inarg.flags |= FUSE_SETUPMAPPING_FLAG_WRITE;
+	args.opcode = FUSE_SETUPMAPPING;
+	args.nodeid = fi->nodeid;
+	args.in_numargs = 1;
+	args.in_args[0].size = sizeof(inarg);
+	args.in_args[0].value = &inarg;
+	err = fuse_simple_request(fm, &args);
+	if (err < 0)
+		return err;
+	dmap->writable = writable;
+	if (!upgrade) {
+		/*
+		 * We don't take a refernce on inode. inode is valid right now
+		 * and when inode is going away, cleanup logic should first
+		 * cleanup dmap entries.
+		 */
+		dmap->inode = inode;
+		dmap->itn.start = dmap->itn.last = start_idx;
+		/* Protected by fi->dax->sem */
+		interval_tree_insert(&dmap->itn, &fi->dax->tree);
+		fi->dax->nr++;
+		spin_lock(&fcd->lock);
+		list_add_tail(&dmap->busy_list, &fcd->busy_ranges);
+		fcd->nr_busy_ranges++;
+		spin_unlock(&fcd->lock);
+	}
+	return 0;
+}
+
+static int fuse_send_removemapping(struct inode *inode,
+				   struct fuse_removemapping_in *inargp,
+				   struct fuse_removemapping_one *remove_one)
+{
+	struct fuse_inode *fi = get_fuse_inode(inode);
+	struct fuse_mount *fm = get_fuse_mount(inode);
+	FUSE_ARGS(args);
+
+	args.opcode = FUSE_REMOVEMAPPING;
+	args.nodeid = fi->nodeid;
+	args.in_numargs = 2;
+	args.in_args[0].size = sizeof(*inargp);
+	args.in_args[0].value = inargp;
+	args.in_args[1].size = inargp->count * sizeof(*remove_one);
+	args.in_args[1].value = remove_one;
+	return fuse_simple_request(fm, &args);
+}
+
+static int dmap_removemapping_list(struct inode *inode, unsigned int num,
+				   struct list_head *to_remove)
+{
+	struct fuse_removemapping_one *remove_one, *ptr;
+	struct fuse_removemapping_in inarg;
+	struct fuse_dax_mapping *dmap;
+	int ret, i = 0, nr_alloc;
+
+	nr_alloc = min_t(unsigned int, num, FUSE_REMOVEMAPPING_MAX_ENTRY);
+	remove_one = kmalloc_array(nr_alloc, sizeof(*remove_one), GFP_NOFS);
+	if (!remove_one)
+		return -ENOMEM;
+
+	ptr = remove_one;
+	list_for_each_entry(dmap, to_remove, list) {
+		ptr->moffset = dmap->window_offset;
+		ptr->len = dmap->length;
+		ptr++;
+		i++;
+		num--;
+		if (i >= nr_alloc || num == 0) {
+			memset(&inarg, 0, sizeof(inarg));
+			inarg.count = i;
+			ret = fuse_send_removemapping(inode, &inarg,
+						      remove_one);
+			if (ret)
+				goto out;
+			ptr = remove_one;
+			i = 0;
+		}
+	}
+out:
+	kfree(remove_one);
+	return ret;
+}
+
+/*
+ * Cleanup dmap entry and add back to free list. This should be called with
+ * fcd->lock held.
+ */
+static void dmap_reinit_add_to_free_pool(struct fuse_conn_dax *fcd,
+					    struct fuse_dax_mapping *dmap)
+{
+	pr_debug("fuse: freeing memory range start_idx=0x%lx end_idx=0x%lx window_offset=0x%llx length=0x%llx\n",
+		 dmap->itn.start, dmap->itn.last, dmap->window_offset,
+		 dmap->length);
+	__dmap_remove_busy_list(fcd, dmap);
+	dmap->inode = NULL;
+	dmap->itn.start = dmap->itn.last = 0;
+	__dmap_add_to_free_pool(fcd, dmap);
+}
+
+/*
+ * Free inode dmap entries whose range falls inside [start, end].
+ * Does not take any locks. At this point of time it should only be
+ * called from evict_inode() path where we know all dmap entries can be
+ * reclaimed.
+ */
+static void inode_reclaim_dmap_range(struct fuse_conn_dax *fcd,
+				     struct inode *inode,
+				     loff_t start, loff_t end)
+{
+	struct fuse_inode *fi = get_fuse_inode(inode);
+	struct fuse_dax_mapping *dmap, *n;
+	int err, num = 0;
+	LIST_HEAD(to_remove);
+	unsigned long start_idx = start >> FUSE_DAX_SHIFT;
+	unsigned long end_idx = end >> FUSE_DAX_SHIFT;
+	struct interval_tree_node *node;
+
+	while (1) {
+		node = interval_tree_iter_first(&fi->dax->tree, start_idx,
+						end_idx);
+		if (!node)
+			break;
+		dmap = node_to_dmap(node);
+		/* inode is going away. There should not be any users of dmap */
+		WARN_ON(refcount_read(&dmap->refcnt) > 1);
+		interval_tree_remove(&dmap->itn, &fi->dax->tree);
+		num++;
+		list_add(&dmap->list, &to_remove);
+	}
+
+	/* Nothing to remove */
+	if (list_empty(&to_remove))
+		return;
+
+	WARN_ON(fi->dax->nr < num);
+	fi->dax->nr -= num;
+	err = dmap_removemapping_list(inode, num, &to_remove);
+	if (err && err != -ENOTCONN) {
+		pr_warn("Failed to removemappings. start=0x%llx end=0x%llx\n",
+			start, end);
+	}
+	spin_lock(&fcd->lock);
+	list_for_each_entry_safe(dmap, n, &to_remove, list) {
+		list_del_init(&dmap->list);
+		dmap_reinit_add_to_free_pool(fcd, dmap);
+	}
+	spin_unlock(&fcd->lock);
+}
+
+static int dmap_removemapping_one(struct inode *inode,
+				  struct fuse_dax_mapping *dmap)
+{
+	struct fuse_removemapping_one forget_one;
+	struct fuse_removemapping_in inarg;
+
+	memset(&inarg, 0, sizeof(inarg));
+	inarg.count = 1;
+	memset(&forget_one, 0, sizeof(forget_one));
+	forget_one.moffset = dmap->window_offset;
+	forget_one.len = dmap->length;
+
+	return fuse_send_removemapping(inode, &inarg, &forget_one);
+}
+
+/*
+ * It is called from evict_inode() and by that time inode is going away. So
+ * this function does not take any locks like fi->dax->sem for traversing
+ * that fuse inode interval tree. If that lock is taken then lock validator
+ * complains of deadlock situation w.r.t fs_reclaim lock.
+ */
+void fuse_dax_inode_cleanup(struct inode *inode)
+{
+	struct fuse_conn *fc = get_fuse_conn(inode);
+	struct fuse_inode *fi = get_fuse_inode(inode);
+
+	/*
+	 * fuse_evict_inode() has already called truncate_inode_pages_final()
+	 * before we arrive here. So we should not have to worry about any
+	 * pages/exception entries still associated with inode.
+	 */
+	inode_reclaim_dmap_range(fc->dax, inode, 0, -1);
+	WARN_ON(fi->dax->nr);
+}
+
+static void fuse_fill_iomap_hole(struct iomap *iomap, loff_t length)
+{
+	iomap->addr = IOMAP_NULL_ADDR;
+	iomap->length = length;
+	iomap->type = IOMAP_HOLE;
+}
+
+static void fuse_fill_iomap(struct inode *inode, loff_t pos, loff_t length,
+			    struct iomap *iomap, struct fuse_dax_mapping *dmap,
+			    unsigned int flags)
+{
+	loff_t offset, len;
+	loff_t i_size = i_size_read(inode);
+
+	offset = pos - (dmap->itn.start << FUSE_DAX_SHIFT);
+	len = min(length, dmap->length - offset);
+
+	/* If length is beyond end of file, truncate further */
+	if (pos + len > i_size)
+		len = i_size - pos;
+
+	if (len > 0) {
+		iomap->addr = dmap->window_offset + offset;
+		iomap->length = len;
+		if (flags & IOMAP_FAULT)
+			iomap->length = ALIGN(len, PAGE_SIZE);
+		iomap->type = IOMAP_MAPPED;
+		/*
+		 * increace refcnt so that reclaim code knows this dmap is in
+		 * use. This assumes fi->dax->sem mutex is held either
+		 * shared/exclusive.
+		 */
+		refcount_inc(&dmap->refcnt);
+
+		/* iomap->private should be NULL */
+		WARN_ON_ONCE(iomap->private);
+		iomap->private = dmap;
+	} else {
+		/* Mapping beyond end of file is hole */
+		fuse_fill_iomap_hole(iomap, length);
+	}
+}
+
+static int fuse_setup_new_dax_mapping(struct inode *inode, loff_t pos,
+				      loff_t length, unsigned int flags,
+				      struct iomap *iomap)
+{
+	struct fuse_inode *fi = get_fuse_inode(inode);
+	struct fuse_conn *fc = get_fuse_conn(inode);
+	struct fuse_conn_dax *fcd = fc->dax;
+	struct fuse_dax_mapping *dmap, *alloc_dmap = NULL;
+	int ret;
+	bool writable = flags & IOMAP_WRITE;
+	unsigned long start_idx = pos >> FUSE_DAX_SHIFT;
+	struct interval_tree_node *node;
+
+	/*
+	 * Can't do inline reclaim in fault path. We call
+	 * dax_layout_busy_page() before we free a range. And
+	 * fuse_wait_dax_page() drops fi->i_mmap_sem lock and requires it.
+	 * In fault path we enter with fi->i_mmap_sem held and can't drop
+	 * it. Also in fault path we hold fi->i_mmap_sem shared and not
+	 * exclusive, so that creates further issues with fuse_wait_dax_page().
+	 * Hence return -EAGAIN and fuse_dax_fault() will wait for a memory
+	 * range to become free and retry.
+	 */
+	if (flags & IOMAP_FAULT) {
+		alloc_dmap = alloc_dax_mapping(fcd);
+		if (!alloc_dmap)
+			return -EAGAIN;
+	} else {
+		alloc_dmap = alloc_dax_mapping_reclaim(fcd, inode);
+		if (IS_ERR(alloc_dmap))
+			return PTR_ERR(alloc_dmap);
+	}
+
+	/* If we are here, we should have memory allocated */
+	if (WARN_ON(!alloc_dmap))
+		return -EIO;
+
+	/*
+	 * Take write lock so that only one caller can try to setup mapping
+	 * and other waits.
+	 */
+	down_write(&fi->dax->sem);
+	/*
+	 * We dropped lock. Check again if somebody else setup
+	 * mapping already.
+	 */
+	node = interval_tree_iter_first(&fi->dax->tree, start_idx, start_idx);
+	if (node) {
+		dmap = node_to_dmap(node);
+		fuse_fill_iomap(inode, pos, length, iomap, dmap, flags);
+		dmap_add_to_free_pool(fcd, alloc_dmap);
+		up_write(&fi->dax->sem);
+		return 0;
+	}
+
+	/* Setup one mapping */
+	ret = fuse_setup_one_mapping(inode, pos >> FUSE_DAX_SHIFT, alloc_dmap,
+				     writable, false);
+	if (ret < 0) {
+		dmap_add_to_free_pool(fcd, alloc_dmap);
+		up_write(&fi->dax->sem);
+		return ret;
+	}
+	fuse_fill_iomap(inode, pos, length, iomap, alloc_dmap, flags);
+	up_write(&fi->dax->sem);
+	return 0;
+}
+
+static int fuse_upgrade_dax_mapping(struct inode *inode, loff_t pos,
+				    loff_t length, unsigned int flags,
+				    struct iomap *iomap)
+{
+	struct fuse_inode *fi = get_fuse_inode(inode);
+	struct fuse_dax_mapping *dmap;
+	int ret;
+	unsigned long idx = pos >> FUSE_DAX_SHIFT;
+	struct interval_tree_node *node;
+
+	/*
+	 * Take exclusive lock so that only one caller can try to setup
+	 * mapping and others wait.
+	 */
+	down_write(&fi->dax->sem);
+	node = interval_tree_iter_first(&fi->dax->tree, idx, idx);
+
+	/* We are holding either inode lock or i_mmap_sem, and that should
+	 * ensure that dmap can't be truncated. We are holding a reference
+	 * on dmap and that should make sure it can't be reclaimed. So dmap
+	 * should still be there in tree despite the fact we dropped and
+	 * re-acquired the fi->dax->sem lock.
+	 */
+	ret = -EIO;
+	if (WARN_ON(!node))
+		goto out_err;
+
+	dmap = node_to_dmap(node);
+
+	/* We took an extra reference on dmap to make sure its not reclaimd.
+	 * Now we hold fi->dax->sem lock and that reference is not needed
+	 * anymore. Drop it.
+	 */
+	if (refcount_dec_and_test(&dmap->refcnt)) {
+		/* refcount should not hit 0. This object only goes
+		 * away when fuse connection goes away
+		 */
+		WARN_ON_ONCE(1);
+	}
+
+	/* Maybe another thread already upgraded mapping while we were not
+	 * holding lock.
+	 */
+	if (dmap->writable) {
+		ret = 0;
+		goto out_fill_iomap;
+	}
+
+	ret = fuse_setup_one_mapping(inode, pos >> FUSE_DAX_SHIFT, dmap, true,
+				     true);
+	if (ret < 0)
+		goto out_err;
+out_fill_iomap:
+	fuse_fill_iomap(inode, pos, length, iomap, dmap, flags);
+out_err:
+	up_write(&fi->dax->sem);
+	return ret;
+}
+
+/* This is just for DAX and the mapping is ephemeral, do not use it for other
+ * purposes since there is no block device with a permanent mapping.
+ */
+static int fuse_iomap_begin(struct inode *inode, loff_t pos, loff_t length,
+			    unsigned int flags, struct iomap *iomap,
+			    struct iomap *srcmap)
+{
+	struct fuse_inode *fi = get_fuse_inode(inode);
+	struct fuse_conn *fc = get_fuse_conn(inode);
+	struct fuse_dax_mapping *dmap;
+	bool writable = flags & IOMAP_WRITE;
+	unsigned long start_idx = pos >> FUSE_DAX_SHIFT;
+	struct interval_tree_node *node;
+
+	/* We don't support FIEMAP */
+	if (WARN_ON(flags & IOMAP_REPORT))
+		return -EIO;
+
+	iomap->offset = pos;
+	iomap->flags = 0;
+	iomap->bdev = NULL;
+	iomap->dax_dev = fc->dax->dev;
+
+	/*
+	 * Both read/write and mmap path can race here. So we need something
+	 * to make sure if we are setting up mapping, then other path waits
+	 *
+	 * For now, use a semaphore for this. It probably needs to be
+	 * optimized later.
+	 */
+	down_read(&fi->dax->sem);
+	node = interval_tree_iter_first(&fi->dax->tree, start_idx, start_idx);
+	if (node) {
+		dmap = node_to_dmap(node);
+		if (writable && !dmap->writable) {
+			/* Upgrade read-only mapping to read-write. This will
+			 * require exclusive fi->dax->sem lock as we don't want
+			 * two threads to be trying to this simultaneously
+			 * for same dmap. So drop shared lock and acquire
+			 * exclusive lock.
+			 *
+			 * Before dropping fi->dax->sem lock, take reference
+			 * on dmap so that its not freed by range reclaim.
+			 */
+			refcount_inc(&dmap->refcnt);
+			up_read(&fi->dax->sem);
+			pr_debug("%s: Upgrading mapping at offset 0x%llx length 0x%llx\n",
+				 __func__, pos, length);
+			return fuse_upgrade_dax_mapping(inode, pos, length,
+							flags, iomap);
+		} else {
+			fuse_fill_iomap(inode, pos, length, iomap, dmap, flags);
+			up_read(&fi->dax->sem);
+			return 0;
+		}
+	} else {
+		up_read(&fi->dax->sem);
+		pr_debug("%s: no mapping at offset 0x%llx length 0x%llx\n",
+				__func__, pos, length);
+		if (pos >= i_size_read(inode))
+			goto iomap_hole;
+
+		return fuse_setup_new_dax_mapping(inode, pos, length, flags,
+						  iomap);
+	}
+
+	/*
+	 * If read beyond end of file happnes, fs code seems to return
+	 * it as hole
+	 */
+iomap_hole:
+	fuse_fill_iomap_hole(iomap, length);
+	pr_debug("%s returning hole mapping. pos=0x%llx length_asked=0x%llx length_returned=0x%llx\n",
+		 __func__, pos, length, iomap->length);
+	return 0;
+}
+
+static int fuse_iomap_end(struct inode *inode, loff_t pos, loff_t length,
+			  ssize_t written, unsigned int flags,
+			  struct iomap *iomap)
+{
+	struct fuse_dax_mapping *dmap = iomap->private;
+
+	if (dmap) {
+		if (refcount_dec_and_test(&dmap->refcnt)) {
+			/* refcount should not hit 0. This object only goes
+			 * away when fuse connection goes away
+			 */
+			WARN_ON_ONCE(1);
+		}
+	}
+
+	/* DAX writes beyond end-of-file aren't handled using iomap, so the
+	 * file size is unchanged and there is nothing to do here.
+	 */
+	return 0;
+}
+
+static const struct iomap_ops fuse_iomap_ops = {
+	.iomap_begin = fuse_iomap_begin,
+	.iomap_end = fuse_iomap_end,
+};
+
+static void fuse_wait_dax_page(struct inode *inode)
+{
+	struct fuse_inode *fi = get_fuse_inode(inode);
+
+	up_write(&fi->i_mmap_sem);
+	schedule();
+	down_write(&fi->i_mmap_sem);
+}
+
+/* Should be called with fi->i_mmap_sem lock held exclusively */
+static int __fuse_dax_break_layouts(struct inode *inode, bool *retry,
+				    loff_t start, loff_t end)
+{
+	struct page *page;
+
+	page = dax_layout_busy_page_range(inode->i_mapping, start, end);
+	if (!page)
+		return 0;
+
+	*retry = true;
+	return ___wait_var_event(&page->_refcount,
+			atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE,
+			0, 0, fuse_wait_dax_page(inode));
+}
+
+/* dmap_end == 0 leads to unmapping of whole file */
+int fuse_dax_break_layouts(struct inode *inode, u64 dmap_start,
+				  u64 dmap_end)
+{
+	bool	retry;
+	int	ret;
+
+	do {
+		retry = false;
+		ret = __fuse_dax_break_layouts(inode, &retry, dmap_start,
+					       dmap_end);
+	} while (ret == 0 && retry);
+
+	return ret;
+}
+
+ssize_t fuse_dax_read_iter(struct kiocb *iocb, struct iov_iter *to)
+{
+	struct inode *inode = file_inode(iocb->ki_filp);
+	ssize_t ret;
+
+	if (iocb->ki_flags & IOCB_NOWAIT) {
+		if (!inode_trylock_shared(inode))
+			return -EAGAIN;
+	} else {
+		inode_lock_shared(inode);
+	}
+
+	ret = dax_iomap_rw(iocb, to, &fuse_iomap_ops);
+	inode_unlock_shared(inode);
+
+	/* TODO file_accessed(iocb->f_filp) */
+	return ret;
+}
+
+static bool file_extending_write(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct inode *inode = file_inode(iocb->ki_filp);
+
+	return (iov_iter_rw(from) == WRITE &&
+		((iocb->ki_pos) >= i_size_read(inode) ||
+		  (iocb->ki_pos + iov_iter_count(from) > i_size_read(inode))));
+}
+
+static ssize_t fuse_dax_direct_write(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct inode *inode = file_inode(iocb->ki_filp);
+	struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(iocb);
+	ssize_t ret;
+
+	ret = fuse_direct_io(&io, from, &iocb->ki_pos, FUSE_DIO_WRITE);
+	if (ret < 0)
+		return ret;
+
+	fuse_invalidate_attr(inode);
+	fuse_write_update_size(inode, iocb->ki_pos);
+	return ret;
+}
+
+ssize_t fuse_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct inode *inode = file_inode(iocb->ki_filp);
+	ssize_t ret;
+
+	if (iocb->ki_flags & IOCB_NOWAIT) {
+		if (!inode_trylock(inode))
+			return -EAGAIN;
+	} else {
+		inode_lock(inode);
+	}
+
+	ret = generic_write_checks(iocb, from);
+	if (ret <= 0)
+		goto out;
+
+	ret = file_remove_privs(iocb->ki_filp);
+	if (ret)
+		goto out;
+	/* TODO file_update_time() but we don't want metadata I/O */
+
+	/* Do not use dax for file extending writes as write and on
+	 * disk i_size increase are not atomic otherwise.
+	 */
+	if (file_extending_write(iocb, from))
+		ret = fuse_dax_direct_write(iocb, from);
+	else
+		ret = dax_iomap_rw(iocb, from, &fuse_iomap_ops);
+
+out:
+	inode_unlock(inode);
+
+	if (ret > 0)
+		ret = generic_write_sync(iocb, ret);
+	return ret;
+}
+
+static int fuse_dax_writepages(struct address_space *mapping,
+			       struct writeback_control *wbc)
+{
+
+	struct inode *inode = mapping->host;
+	struct fuse_conn *fc = get_fuse_conn(inode);
+
+	return dax_writeback_mapping_range(mapping, fc->dax->dev, wbc);
+}
+
+static vm_fault_t __fuse_dax_fault(struct vm_fault *vmf,
+				   enum page_entry_size pe_size, bool write)
+{
+	vm_fault_t ret;
+	struct inode *inode = file_inode(vmf->vma->vm_file);
+	struct super_block *sb = inode->i_sb;
+	pfn_t pfn;
+	int error = 0;
+	struct fuse_conn *fc = get_fuse_conn(inode);
+	struct fuse_conn_dax *fcd = fc->dax;
+	bool retry = false;
+
+	if (write)
+		sb_start_pagefault(sb);
+retry:
+	if (retry && !(fcd->nr_free_ranges > 0))
+		wait_event(fcd->range_waitq, (fcd->nr_free_ranges > 0));
+
+	/*
+	 * We need to serialize against not only truncate but also against
+	 * fuse dax memory range reclaim. While a range is being reclaimed,
+	 * we do not want any read/write/mmap to make progress and try
+	 * to populate page cache or access memory we are trying to free.
+	 */
+	down_read(&get_fuse_inode(inode)->i_mmap_sem);
+	ret = dax_iomap_fault(vmf, pe_size, &pfn, &error, &fuse_iomap_ops);
+	if ((ret & VM_FAULT_ERROR) && error == -EAGAIN) {
+		error = 0;
+		retry = true;
+		up_read(&get_fuse_inode(inode)->i_mmap_sem);
+		goto retry;
+	}
+
+	if (ret & VM_FAULT_NEEDDSYNC)
+		ret = dax_finish_sync_fault(vmf, pe_size, pfn);
+	up_read(&get_fuse_inode(inode)->i_mmap_sem);
+
+	if (write)
+		sb_end_pagefault(sb);
+
+	return ret;
+}
+
+static vm_fault_t fuse_dax_fault(struct vm_fault *vmf)
+{
+	return __fuse_dax_fault(vmf, PE_SIZE_PTE,
+				vmf->flags & FAULT_FLAG_WRITE);
+}
+
+static vm_fault_t fuse_dax_huge_fault(struct vm_fault *vmf,
+			       enum page_entry_size pe_size)
+{
+	return __fuse_dax_fault(vmf, pe_size, vmf->flags & FAULT_FLAG_WRITE);
+}
+
+static vm_fault_t fuse_dax_page_mkwrite(struct vm_fault *vmf)
+{
+	return __fuse_dax_fault(vmf, PE_SIZE_PTE, true);
+}
+
+static vm_fault_t fuse_dax_pfn_mkwrite(struct vm_fault *vmf)
+{
+	return __fuse_dax_fault(vmf, PE_SIZE_PTE, true);
+}
+
+static const struct vm_operations_struct fuse_dax_vm_ops = {
+	.fault		= fuse_dax_fault,
+	.huge_fault	= fuse_dax_huge_fault,
+	.page_mkwrite	= fuse_dax_page_mkwrite,
+	.pfn_mkwrite	= fuse_dax_pfn_mkwrite,
+};
+
+int fuse_dax_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	file_accessed(file);
+	vma->vm_ops = &fuse_dax_vm_ops;
+	vma->vm_flags |= VM_MIXEDMAP | VM_HUGEPAGE;
+	return 0;
+}
+
+static int dmap_writeback_invalidate(struct inode *inode,
+				     struct fuse_dax_mapping *dmap)
+{
+	int ret;
+	loff_t start_pos = dmap->itn.start << FUSE_DAX_SHIFT;
+	loff_t end_pos = (start_pos + FUSE_DAX_SZ - 1);
+
+	ret = filemap_fdatawrite_range(inode->i_mapping, start_pos, end_pos);
+	if (ret) {
+		pr_debug("fuse: filemap_fdatawrite_range() failed. err=%d start_pos=0x%llx, end_pos=0x%llx\n",
+			 ret, start_pos, end_pos);
+		return ret;
+	}
+
+	ret = invalidate_inode_pages2_range(inode->i_mapping,
+					    start_pos >> PAGE_SHIFT,
+					    end_pos >> PAGE_SHIFT);
+	if (ret)
+		pr_debug("fuse: invalidate_inode_pages2_range() failed err=%d\n",
+			 ret);
+
+	return ret;
+}
+
+static int reclaim_one_dmap_locked(struct inode *inode,
+				   struct fuse_dax_mapping *dmap)
+{
+	int ret;
+	struct fuse_inode *fi = get_fuse_inode(inode);
+
+	/*
+	 * igrab() was done to make sure inode won't go under us, and this
+	 * further avoids the race with evict().
+	 */
+	ret = dmap_writeback_invalidate(inode, dmap);
+	if (ret)
+		return ret;
+
+	/* Remove dax mapping from inode interval tree now */
+	interval_tree_remove(&dmap->itn, &fi->dax->tree);
+	fi->dax->nr--;
+
+	/* It is possible that umount/shutdown has killed the fuse connection
+	 * and worker thread is trying to reclaim memory in parallel.  Don't
+	 * warn in that case.
+	 */
+	ret = dmap_removemapping_one(inode, dmap);
+	if (ret && ret != -ENOTCONN) {
+		pr_warn("Failed to remove mapping. offset=0x%llx len=0x%llx ret=%d\n",
+			dmap->window_offset, dmap->length, ret);
+	}
+	return 0;
+}
+
+/* Find first mapped dmap for an inode and return file offset. Caller needs
+ * to hold fi->dax->sem lock either shared or exclusive.
+ */
+static struct fuse_dax_mapping *inode_lookup_first_dmap(struct inode *inode)
+{
+	struct fuse_inode *fi = get_fuse_inode(inode);
+	struct fuse_dax_mapping *dmap;
+	struct interval_tree_node *node;
+
+	for (node = interval_tree_iter_first(&fi->dax->tree, 0, -1); node;
+	     node = interval_tree_iter_next(node, 0, -1)) {
+		dmap = node_to_dmap(node);
+		/* still in use. */
+		if (refcount_read(&dmap->refcnt) > 1)
+			continue;
+
+		return dmap;
+	}
+
+	return NULL;
+}
+
+/*
+ * Find first mapping in the tree and free it and return it. Do not add
+ * it back to free pool.
+ */
+static struct fuse_dax_mapping *
+inode_inline_reclaim_one_dmap(struct fuse_conn_dax *fcd, struct inode *inode,
+			      bool *retry)
+{
+	struct fuse_inode *fi = get_fuse_inode(inode);
+	struct fuse_dax_mapping *dmap;
+	u64 dmap_start, dmap_end;
+	unsigned long start_idx;
+	int ret;
+	struct interval_tree_node *node;
+
+	down_write(&fi->i_mmap_sem);
+
+	/* Lookup a dmap and corresponding file offset to reclaim. */
+	down_read(&fi->dax->sem);
+	dmap = inode_lookup_first_dmap(inode);
+	if (dmap) {
+		start_idx = dmap->itn.start;
+		dmap_start = start_idx << FUSE_DAX_SHIFT;
+		dmap_end = dmap_start + FUSE_DAX_SZ - 1;
+	}
+	up_read(&fi->dax->sem);
+
+	if (!dmap)
+		goto out_mmap_sem;
+	/*
+	 * Make sure there are no references to inode pages using
+	 * get_user_pages()
+	 */
+	ret = fuse_dax_break_layouts(inode, dmap_start, dmap_end);
+	if (ret) {
+		pr_debug("fuse: fuse_dax_break_layouts() failed. err=%d\n",
+			 ret);
+		dmap = ERR_PTR(ret);
+		goto out_mmap_sem;
+	}
+
+	down_write(&fi->dax->sem);
+	node = interval_tree_iter_first(&fi->dax->tree, start_idx, start_idx);
+	/* Range already got reclaimed by somebody else */
+	if (!node) {
+		if (retry)
+			*retry = true;
+		goto out_write_dmap_sem;
+	}
+
+	dmap = node_to_dmap(node);
+	/* still in use. */
+	if (refcount_read(&dmap->refcnt) > 1) {
+		dmap = NULL;
+		if (retry)
+			*retry = true;
+		goto out_write_dmap_sem;
+	}
+
+	ret = reclaim_one_dmap_locked(inode, dmap);
+	if (ret < 0) {
+		dmap = ERR_PTR(ret);
+		goto out_write_dmap_sem;
+	}
+
+	/* Clean up dmap. Do not add back to free list */
+	dmap_remove_busy_list(fcd, dmap);
+	dmap->inode = NULL;
+	dmap->itn.start = dmap->itn.last = 0;
+
+	pr_debug("fuse: %s: inline reclaimed memory range. inode=%p, window_offset=0x%llx, length=0x%llx\n",
+		 __func__, inode, dmap->window_offset, dmap->length);
+
+out_write_dmap_sem:
+	up_write(&fi->dax->sem);
+out_mmap_sem:
+	up_write(&fi->i_mmap_sem);
+	return dmap;
+}
+
+static struct fuse_dax_mapping *
+alloc_dax_mapping_reclaim(struct fuse_conn_dax *fcd, struct inode *inode)
+{
+	struct fuse_dax_mapping *dmap;
+	struct fuse_inode *fi = get_fuse_inode(inode);
+
+	while (1) {
+		bool retry = false;
+
+		dmap = alloc_dax_mapping(fcd);
+		if (dmap)
+			return dmap;
+
+		dmap = inode_inline_reclaim_one_dmap(fcd, inode, &retry);
+		/*
+		 * Either we got a mapping or it is an error, return in both
+		 * the cases.
+		 */
+		if (dmap)
+			return dmap;
+
+		/* If we could not reclaim a mapping because it
+		 * had a reference or some other temporary failure,
+		 * Try again. We want to give up inline reclaim only
+		 * if there is no range assigned to this node. Otherwise
+		 * if a deadlock is possible if we sleep with fi->i_mmap_sem
+		 * held and worker to free memory can't make progress due
+		 * to unavailability of fi->i_mmap_sem lock. So sleep
+		 * only if fi->dax->nr=0
+		 */
+		if (retry)
+			continue;
+		/*
+		 * There are no mappings which can be reclaimed. Wait for one.
+		 * We are not holding fi->dax->sem. So it is possible
+		 * that range gets added now. But as we are not holding
+		 * fi->i_mmap_sem, worker should still be able to free up
+		 * a range and wake us up.
+		 */
+		if (!fi->dax->nr && !(fcd->nr_free_ranges > 0)) {
+			if (wait_event_killable_exclusive(fcd->range_waitq,
+					(fcd->nr_free_ranges > 0))) {
+				return ERR_PTR(-EINTR);
+			}
+		}
+	}
+}
+
+static int lookup_and_reclaim_dmap_locked(struct fuse_conn_dax *fcd,
+					  struct inode *inode,
+					  unsigned long start_idx)
+{
+	int ret;
+	struct fuse_inode *fi = get_fuse_inode(inode);
+	struct fuse_dax_mapping *dmap;
+	struct interval_tree_node *node;
+
+	/* Find fuse dax mapping at file offset inode. */
+	node = interval_tree_iter_first(&fi->dax->tree, start_idx, start_idx);
+
+	/* Range already got cleaned up by somebody else */
+	if (!node)
+		return 0;
+	dmap = node_to_dmap(node);
+
+	/* still in use. */
+	if (refcount_read(&dmap->refcnt) > 1)
+		return 0;
+
+	ret = reclaim_one_dmap_locked(inode, dmap);
+	if (ret < 0)
+		return ret;
+
+	/* Cleanup dmap entry and add back to free list */
+	spin_lock(&fcd->lock);
+	dmap_reinit_add_to_free_pool(fcd, dmap);
+	spin_unlock(&fcd->lock);
+	return ret;
+}
+
+/*
+ * Free a range of memory.
+ * Locking:
+ * 1. Take fi->i_mmap_sem to block dax faults.
+ * 2. Take fi->dax->sem to protect interval tree and also to make sure
+ *    read/write can not reuse a dmap which we might be freeing.
+ */
+static int lookup_and_reclaim_dmap(struct fuse_conn_dax *fcd,
+				   struct inode *inode,
+				   unsigned long start_idx,
+				   unsigned long end_idx)
+{
+	int ret;
+	struct fuse_inode *fi = get_fuse_inode(inode);
+	loff_t dmap_start = start_idx << FUSE_DAX_SHIFT;
+	loff_t dmap_end = (dmap_start + FUSE_DAX_SZ) - 1;
+
+	down_write(&fi->i_mmap_sem);
+	ret = fuse_dax_break_layouts(inode, dmap_start, dmap_end);
+	if (ret) {
+		pr_debug("virtio_fs: fuse_dax_break_layouts() failed. err=%d\n",
+			 ret);
+		goto out_mmap_sem;
+	}
+
+	down_write(&fi->dax->sem);
+	ret = lookup_and_reclaim_dmap_locked(fcd, inode, start_idx);
+	up_write(&fi->dax->sem);
+out_mmap_sem:
+	up_write(&fi->i_mmap_sem);
+	return ret;
+}
+
+static int try_to_free_dmap_chunks(struct fuse_conn_dax *fcd,
+				   unsigned long nr_to_free)
+{
+	struct fuse_dax_mapping *dmap, *pos, *temp;
+	int ret, nr_freed = 0;
+	unsigned long start_idx = 0, end_idx = 0;
+	struct inode *inode = NULL;
+
+	/* Pick first busy range and free it for now*/
+	while (1) {
+		if (nr_freed >= nr_to_free)
+			break;
+
+		dmap = NULL;
+		spin_lock(&fcd->lock);
+
+		if (!fcd->nr_busy_ranges) {
+			spin_unlock(&fcd->lock);
+			return 0;
+		}
+
+		list_for_each_entry_safe(pos, temp, &fcd->busy_ranges,
+						busy_list) {
+			/* skip this range if it's in use. */
+			if (refcount_read(&pos->refcnt) > 1)
+				continue;
+
+			inode = igrab(pos->inode);
+			/*
+			 * This inode is going away. That will free
+			 * up all the ranges anyway, continue to
+			 * next range.
+			 */
+			if (!inode)
+				continue;
+			/*
+			 * Take this element off list and add it tail. If
+			 * this element can't be freed, it will help with
+			 * selecting new element in next iteration of loop.
+			 */
+			dmap = pos;
+			list_move_tail(&dmap->busy_list, &fcd->busy_ranges);
+			start_idx = end_idx = dmap->itn.start;
+			break;
+		}
+		spin_unlock(&fcd->lock);
+		if (!dmap)
+			return 0;
+
+		ret = lookup_and_reclaim_dmap(fcd, inode, start_idx, end_idx);
+		iput(inode);
+		if (ret)
+			return ret;
+		nr_freed++;
+	}
+	return 0;
+}
+
+static void fuse_dax_free_mem_worker(struct work_struct *work)
+{
+	int ret;
+	struct fuse_conn_dax *fcd = container_of(work, struct fuse_conn_dax,
+						 free_work.work);
+	ret = try_to_free_dmap_chunks(fcd, FUSE_DAX_RECLAIM_CHUNK);
+	if (ret) {
+		pr_debug("fuse: try_to_free_dmap_chunks() failed with err=%d\n",
+			 ret);
+	}
+
+	/* If number of free ranges are still below threhold, requeue */
+	kick_dmap_free_worker(fcd, 1);
+}
+
+static void fuse_free_dax_mem_ranges(struct list_head *mem_list)
+{
+	struct fuse_dax_mapping *range, *temp;
+
+	/* Free All allocated elements */
+	list_for_each_entry_safe(range, temp, mem_list, list) {
+		list_del(&range->list);
+		if (!list_empty(&range->busy_list))
+			list_del(&range->busy_list);
+		kfree(range);
+	}
+}
+
+void fuse_dax_conn_free(struct fuse_conn *fc)
+{
+	if (fc->dax) {
+		fuse_free_dax_mem_ranges(&fc->dax->free_ranges);
+		kfree(fc->dax);
+		fc->dax = NULL;
+	}
+}
+
+static int fuse_dax_mem_range_init(struct fuse_conn_dax *fcd)
+{
+	long nr_pages, nr_ranges;
+	void *kaddr;
+	pfn_t pfn;
+	struct fuse_dax_mapping *range;
+	int ret, id;
+	size_t dax_size = -1;
+	unsigned long i;
+
+	init_waitqueue_head(&fcd->range_waitq);
+	INIT_LIST_HEAD(&fcd->free_ranges);
+	INIT_LIST_HEAD(&fcd->busy_ranges);
+	INIT_DELAYED_WORK(&fcd->free_work, fuse_dax_free_mem_worker);
+
+	id = dax_read_lock();
+	nr_pages = dax_direct_access(fcd->dev, 0, PHYS_PFN(dax_size), &kaddr,
+				     &pfn);
+	dax_read_unlock(id);
+	if (nr_pages < 0) {
+		pr_debug("dax_direct_access() returned %ld\n", nr_pages);
+		return nr_pages;
+	}
+
+	nr_ranges = nr_pages/FUSE_DAX_PAGES;
+	pr_debug("%s: dax mapped %ld pages. nr_ranges=%ld\n",
+		__func__, nr_pages, nr_ranges);
+
+	for (i = 0; i < nr_ranges; i++) {
+		range = kzalloc(sizeof(struct fuse_dax_mapping), GFP_KERNEL);
+		ret = -ENOMEM;
+		if (!range)
+			goto out_err;
+
+		/* TODO: This offset only works if virtio-fs driver is not
+		 * having some memory hidden at the beginning. This needs
+		 * better handling
+		 */
+		range->window_offset = i * FUSE_DAX_SZ;
+		range->length = FUSE_DAX_SZ;
+		INIT_LIST_HEAD(&range->busy_list);
+		refcount_set(&range->refcnt, 1);
+		list_add_tail(&range->list, &fcd->free_ranges);
+	}
+
+	fcd->nr_free_ranges = nr_ranges;
+	fcd->nr_ranges = nr_ranges;
+	return 0;
+out_err:
+	/* Free All allocated elements */
+	fuse_free_dax_mem_ranges(&fcd->free_ranges);
+	return ret;
+}
+
+int fuse_dax_conn_alloc(struct fuse_conn *fc, struct dax_device *dax_dev)
+{
+	struct fuse_conn_dax *fcd;
+	int err;
+
+	if (!dax_dev)
+		return 0;
+
+	fcd = kzalloc(sizeof(*fcd), GFP_KERNEL);
+	if (!fcd)
+		return -ENOMEM;
+
+	spin_lock_init(&fcd->lock);
+	fcd->dev = dax_dev;
+	err = fuse_dax_mem_range_init(fcd);
+	if (err) {
+		kfree(fcd);
+		return err;
+	}
+
+	fc->dax = fcd;
+	return 0;
+}
+
+bool fuse_dax_inode_alloc(struct super_block *sb, struct fuse_inode *fi)
+{
+	struct fuse_conn *fc = get_fuse_conn_super(sb);
+
+	fi->dax = NULL;
+	if (fc->dax) {
+		fi->dax = kzalloc(sizeof(*fi->dax), GFP_KERNEL_ACCOUNT);
+		if (!fi->dax)
+			return false;
+
+		init_rwsem(&fi->dax->sem);
+		fi->dax->tree = RB_ROOT_CACHED;
+	}
+
+	return true;
+}
+
+static const struct address_space_operations fuse_dax_file_aops  = {
+	.writepages	= fuse_dax_writepages,
+	.direct_IO	= noop_direct_IO,
+	.set_page_dirty	= noop_set_page_dirty,
+	.invalidatepage	= noop_invalidatepage,
+};
+
+void fuse_dax_inode_init(struct inode *inode)
+{
+	struct fuse_conn *fc = get_fuse_conn(inode);
+
+	if (!fc->dax)
+		return;
+
+	inode->i_flags |= S_DAX;
+	inode->i_data.a_ops = &fuse_dax_file_aops;
+}
+
+bool fuse_dax_check_alignment(struct fuse_conn *fc, unsigned int map_alignment)
+{
+	if (fc->dax && (map_alignment > FUSE_DAX_SHIFT)) {
+		pr_warn("FUSE: map_alignment %u incompatible with dax mem range size %u\n",
+			map_alignment, FUSE_DAX_SZ);
+		return false;
+	}
+	return true;
+}
+
+void fuse_dax_cancel_work(struct fuse_conn *fc)
+{
+	struct fuse_conn_dax *fcd = fc->dax;
+
+	if (fcd)
+		cancel_delayed_work_sync(&fcd->free_work);
+
+}
+EXPORT_SYMBOL_GPL(fuse_dax_cancel_work);