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    SubjectRe: [PATCH 20/20] fuse,virtiofs: Add logic to free up a memory range
    On Wed, Mar 04, 2020 at 11:58:45AM -0500, Vivek Goyal wrote:
    > Add logic to free up a busy memory range. Freed memory range will be
    > returned to free pool. Add a worker which can be started to select
    > and free some busy memory ranges.
    >
    > Process can also steal one of its busy dax ranges if free range is not
    > available. I will refer it to as direct reclaim.
    >
    > If free range is not available and nothing can't be stolen from same
    > inode, caller waits on a waitq for free range to become available.
    >
    > For reclaiming a range, as of now we need to hold following locks in
    > specified order.
    >
    > down_write(&fi->i_mmap_sem);
    > down_write(&fi->i_dmap_sem);
    >
    > We look for a free range in following order.
    >
    > A. Try to get a free range.
    > B. If not, try direct reclaim.
    > C. If not, wait for a memory range to become free
    >
    > Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
    > Signed-off-by: Liu Bo <bo.liu@linux.alibaba.com>
    > ---
    > fs/fuse/file.c | 450 ++++++++++++++++++++++++++++++++++++++++++++++-
    > fs/fuse/fuse_i.h | 25 +++
    > fs/fuse/inode.c | 5 +
    > 3 files changed, 473 insertions(+), 7 deletions(-)
    >
    > diff --git a/fs/fuse/file.c b/fs/fuse/file.c
    > index 8b264fcb9b3c..61ae2ddeef55 100644
    > --- a/fs/fuse/file.c
    > +++ b/fs/fuse/file.c
    > @@ -8,6 +8,7 @@
    >
    > #include "fuse_i.h"
    >
    > +#include <linux/delay.h>
    > #include <linux/pagemap.h>
    > #include <linux/slab.h>
    > #include <linux/kernel.h>
    > @@ -37,6 +38,8 @@ static struct page **fuse_pages_alloc(unsigned int npages, gfp_t flags,
    > return pages;
    > }
    >
    > +static struct fuse_dax_mapping *alloc_dax_mapping_reclaim(struct fuse_conn *fc,
    > + struct inode *inode, bool fault);
    > static int fuse_send_open(struct fuse_conn *fc, u64 nodeid, struct file *file,
    > int opcode, struct fuse_open_out *outargp)
    > {
    > @@ -193,6 +196,28 @@ static void fuse_link_write_file(struct file *file)
    > spin_unlock(&fi->lock);
    > }
    >
    > +static void
    > +__kick_dmap_free_worker(struct fuse_conn *fc, unsigned long delay_ms)
    > +{
    > + unsigned long free_threshold;
    > +
    > + /* If number of free ranges are below threshold, start reclaim */
    > + free_threshold = max((fc->nr_ranges * FUSE_DAX_RECLAIM_THRESHOLD)/100,
    > + (unsigned long)1);
    > + if (fc->nr_free_ranges < free_threshold) {
    > + pr_debug("fuse: Kicking dax memory reclaim worker. nr_free_ranges=0x%ld nr_total_ranges=%ld\n", fc->nr_free_ranges, fc->nr_ranges);
    > + queue_delayed_work(system_long_wq, &fc->dax_free_work,
    > + msecs_to_jiffies(delay_ms));
    > + }
    > +}
    > +
    > +static void kick_dmap_free_worker(struct fuse_conn *fc, unsigned long delay_ms)
    > +{
    > + spin_lock(&fc->lock);
    > + __kick_dmap_free_worker(fc, delay_ms);
    > + spin_unlock(&fc->lock);
    > +}
    > +
    > static struct fuse_dax_mapping *alloc_dax_mapping(struct fuse_conn *fc)
    > {
    > struct fuse_dax_mapping *dmap = NULL;
    > @@ -201,7 +226,7 @@ static struct fuse_dax_mapping *alloc_dax_mapping(struct fuse_conn *fc)
    >
    > if (fc->nr_free_ranges <= 0) {
    > spin_unlock(&fc->lock);
    > - return NULL;
    > + goto out_kick;
    > }
    >
    > WARN_ON(list_empty(&fc->free_ranges));
    > @@ -212,6 +237,9 @@ static struct fuse_dax_mapping *alloc_dax_mapping(struct fuse_conn *fc)
    > list_del_init(&dmap->list);
    > fc->nr_free_ranges--;
    > spin_unlock(&fc->lock);
    > +
    > +out_kick:
    > + kick_dmap_free_worker(fc, 0);
    > return dmap;
    > }
    >
    > @@ -238,6 +266,7 @@ static void __dmap_add_to_free_pool(struct fuse_conn *fc,
    > {
    > list_add_tail(&dmap->list, &fc->free_ranges);
    > fc->nr_free_ranges++;
    > + wake_up(&fc->dax_range_waitq);
    > }
    >
    > static void dmap_add_to_free_pool(struct fuse_conn *fc,
    > @@ -289,6 +318,12 @@ static int fuse_setup_one_mapping(struct inode *inode, loff_t offset,
    >
    > 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->start = offset;
    > dmap->end = offset + FUSE_DAX_MEM_RANGE_SZ - 1;
    > /* Protected by fi->i_dmap_sem */
    > @@ -368,6 +403,7 @@ static void dmap_reinit_add_to_free_pool(struct fuse_conn *fc,
    > "window_offset=0x%llx length=0x%llx\n", dmap->start,
    > dmap->end, dmap->window_offset, dmap->length);
    > __dmap_remove_busy_list(fc, dmap);
    > + dmap->inode = NULL;
    > dmap->start = dmap->end = 0;
    > __dmap_add_to_free_pool(fc, dmap);
    > }
    > @@ -386,7 +422,8 @@ static void inode_reclaim_dmap_range(struct fuse_conn *fc, struct inode *inode,
    > int err, num = 0;
    > LIST_HEAD(to_remove);
    >
    > - pr_debug("fuse: %s: start=0x%llx, end=0x%llx\n", __func__, start, end);
    > + pr_debug("fuse: %s: inode=0x%px start=0x%llx, end=0x%llx\n", __func__,
    > + inode, start, end);
    >
    > /*
    > * Interval tree search matches intersecting entries. Adjust the range
    > @@ -400,6 +437,8 @@ static void inode_reclaim_dmap_range(struct fuse_conn *fc, struct inode *inode,
    > end);
    > if (!dmap)
    > break;
    > + /* inode is going away. There should not be any users of dmap */
    > + WARN_ON(refcount_read(&dmap->refcnt) > 1);
    > fuse_dax_interval_tree_remove(dmap, &fi->dmap_tree);
    > num++;
    > list_add(&dmap->list, &to_remove);
    > @@ -434,6 +473,21 @@ static void inode_reclaim_dmap_range(struct fuse_conn *fc, struct inode *inode,
    > spin_unlock(&fc->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->i_dmap_sem for traversing
    > @@ -1903,6 +1957,17 @@ static void fuse_fill_iomap(struct inode *inode, loff_t pos, loff_t length,
    > 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 i_dmap_sem mutex is held either
    > + * shared/exclusive.
    > + */
    > + refcount_inc(&dmap->refcnt);
    > +
    > + /* iomap->private should be NULL */
    > + WARN_ON_ONCE(iomap->private);
    > + iomap->private = dmap;
    > +
    > pr_debug("%s: returns iomap: addr 0x%llx offset 0x%llx"
    > " length 0x%llx\n", __func__, iomap->addr,
    > iomap->offset, iomap->length);
    > @@ -1925,8 +1990,12 @@ static int iomap_begin_setup_new_mapping(struct inode *inode, loff_t pos,
    > int ret;
    > bool writable = flags & IOMAP_WRITE;
    >
    > - alloc_dmap = alloc_dax_mapping(fc);
    > - if (!alloc_dmap)
    > + alloc_dmap = alloc_dax_mapping_reclaim(fc, inode, flags & IOMAP_FAULT);
    > + 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 -EBUSY;
    >
    > /*
    > @@ -1979,14 +2048,25 @@ static int iomap_begin_upgrade_mapping(struct inode *inode, loff_t pos,
    > dmap = fuse_dax_interval_tree_iter_first(&fi->dmap_tree, pos, pos);
    >
    > /* We are holding either inode lock or i_mmap_sem, and that should
    > - * ensure that dmap can't reclaimed or truncated and it should still
    > - * be there in tree despite the fact we dropped and re-acquired the
    > - * lock.
    > + * 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 i_dmap_sem lock.
    > */
    > ret = -EIO;
    > if (WARN_ON(!dmap))
    > goto out_err;
    >
    > + /* We took an extra reference on dmap to make sure its not reclaimd.
    > + * Now we hold i_dmap_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.
    > */
    > @@ -2056,7 +2136,11 @@ static int fuse_iomap_begin(struct inode *inode, loff_t pos, loff_t length,
    > * two threads to be trying to this simultaneously
    > * for same dmap. So drop shared lock and acquire
    > * exclusive lock.
    > + *
    > + * Before dropping i_dmap_sem lock, take reference
    > + * on dmap so that its not freed by range reclaim.
    > */
    > + refcount_inc(&dmap->refcnt);
    > up_read(&fi->i_dmap_sem);
    > pr_debug("%s: Upgrading mapping at offset 0x%llx"
    > " length 0x%llx\n", __func__, pos, length);
    > @@ -2092,6 +2176,16 @@ static int fuse_iomap_end(struct inode *inode, loff_t pos, loff_t length,
    > ssize_t written, unsigned 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.
    > */
    > @@ -4103,3 +4197,345 @@ void fuse_init_file_inode(struct inode *inode)
    > inode->i_data.a_ops = &fuse_dax_file_aops;
    > }
    > }
    > +
    > +static int dmap_writeback_invalidate(struct inode *inode,
    > + struct fuse_dax_mapping *dmap)
    > +{
    > + int ret;
    > +
    > + ret = filemap_fdatawrite_range(inode->i_mapping, dmap->start,
    > + dmap->end);
    > + if (ret) {
    > + printk("filemap_fdatawrite_range() failed. err=%d start=0x%llx,"
    > + " end=0x%llx\n", ret, dmap->start, dmap->end);
    > + return ret;
    > + }
    > +
    > + ret = invalidate_inode_pages2_range(inode->i_mapping,
    > + dmap->start >> PAGE_SHIFT,
    > + dmap->end >> PAGE_SHIFT);
    > + if (ret)
    > + printk("invalidate_inode_pages2_range() failed err=%d\n", ret);
    > +
    > + return ret;
    > +}
    > +
    > +static int reclaim_one_dmap_locked(struct fuse_conn *fc, 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 */
    > + fuse_dax_interval_tree_remove(dmap, &fi->dmap_tree);
    > + fi->nr_dmaps--;
    > +
    > + /* It is possible that umount/shutodwn has killed the fuse connection
    > + * and worker thread is trying to reclaim memory in parallel. So check
    > + * if connection is still up or not otherwise don't send removemapping
    > + * message.
    > + */
    > + if (fc->connected) {
    > + ret = dmap_removemapping_one(inode, dmap);
    > + if (ret) {
    > + pr_warn("Failed to remove mapping. offset=0x%llx"
    > + " len=0x%llx ret=%d\n", dmap->window_offset,
    > + dmap->length, ret);
    > + }
    > + }
    > + return 0;
    > +}
    > +
    > +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_break_dax_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 */
    > +static int fuse_break_dax_layouts(struct inode *inode, u64 dmap_start,
    > + u64 dmap_end)
    > +{
    > + bool retry;
    > + int ret;
    > +
    > + do {
    > + retry = false;
    > + ret = __fuse_break_dax_layouts(inode, &retry, dmap_start,
    > + dmap_end);
    > + } while (ret == 0 && retry);
    > +
    > + return ret;
    > +}
    > +
    > +/* Find first mapping in the tree and free it. */
    > +static struct fuse_dax_mapping *
    > +inode_reclaim_one_dmap_locked(struct fuse_conn *fc, struct inode *inode)
    > +{
    > + struct fuse_inode *fi = get_fuse_inode(inode);
    > + struct fuse_dax_mapping *dmap;
    > + int ret;
    > +
    > + for (dmap = fuse_dax_interval_tree_iter_first(&fi->dmap_tree, 0, -1);
    > + dmap;
    > + dmap = fuse_dax_interval_tree_iter_next(dmap, 0, -1)) {
    > + /* still in use. */
    > + if (refcount_read(&dmap->refcnt) > 1)
    > + continue;
    > +
    > + ret = reclaim_one_dmap_locked(fc, inode, dmap);
    > + if (ret < 0)
    > + return ERR_PTR(ret);
    > +
    > + /* Clean up dmap. Do not add back to free list */
    > + dmap_remove_busy_list(fc, dmap);
    > + dmap->inode = NULL;
    > + dmap->start = dmap->end = 0;
    > +
    > + pr_debug("fuse: %s: reclaimed memory range. inode=%px,"
    > + " window_offset=0x%llx, length=0x%llx\n", __func__,
    > + inode, dmap->window_offset, dmap->length);
    > + return dmap;
    > + }
    > +
    > + return NULL;
    > +}
    > +
    > +/*
    > + * Find first mapping in the tree and free it and return it. Do not add
    > + * it back to free pool. If fault == true, this function should be called
    > + * with fi->i_mmap_sem held.
    > + */
    > +static struct fuse_dax_mapping *inode_reclaim_one_dmap(struct fuse_conn *fc,
    > + struct inode *inode,
    > + bool fault)
    > +{
    > + struct fuse_inode *fi = get_fuse_inode(inode);
    > + struct fuse_dax_mapping *dmap;
    > + int ret;
    > +
    > + if (!fault)
    > + down_write(&fi->i_mmap_sem);
    > +
    > + /*
    > + * Make sure there are no references to inode pages using
    > + * get_user_pages()
    > + */
    > + ret = fuse_break_dax_layouts(inode, 0, 0);

    Hi Vivek,

    This patch is enabling inline reclaim for fault path, but fault path
    has already holds a locked exceptional entry which I believe the above
    fuse_break_dax_layouts() needs to wait for, can you please elaborate
    on how this can be avoided?

    thanks,
    liubo


    > + if (ret) {
    > + printk("virtio_fs: fuse_break_dax_layouts() failed. err=%d\n",
    > + ret);
    > + dmap = ERR_PTR(ret);
    > + goto out_mmap_sem;
    > + }
    > + down_write(&fi->i_dmap_sem);
    > + dmap = inode_reclaim_one_dmap_locked(fc, inode);
    > + up_write(&fi->i_dmap_sem);
    > +out_mmap_sem:
    > + if (!fault)
    > + up_write(&fi->i_mmap_sem);
    > + return dmap;
    > +}
    > +
    > +/* If fault == true, it should be called with fi->i_mmap_sem locked */
    > +static struct fuse_dax_mapping *alloc_dax_mapping_reclaim(struct fuse_conn *fc,
    > + struct inode *inode, bool fault)
    > +{
    > + struct fuse_dax_mapping *dmap;
    > + struct fuse_inode *fi = get_fuse_inode(inode);
    > +
    > + while(1) {
    > + dmap = alloc_dax_mapping(fc);
    > + if (dmap)
    > + return dmap;
    > +
    > + if (fi->nr_dmaps) {
    > + dmap = inode_reclaim_one_dmap(fc, inode, fault);
    > + if (dmap)
    > + return dmap;
    > + /* If we could not reclaim a mapping because it
    > + * had a reference, that should be a temporary
    > + * situation. Try again.
    > + */
    > + msleep(1);
    > + continue;
    > + }
    > + /*
    > + * There are no mappings which can be reclaimed.
    > + * Wait for one.
    > + */
    > + if (!(fc->nr_free_ranges > 0)) {
    > + if (wait_event_killable_exclusive(fc->dax_range_waitq,
    > + (fc->nr_free_ranges > 0)))
    > + return ERR_PTR(-EINTR);
    > + }
    > + }
    > +}
    > +
    > +static int lookup_and_reclaim_dmap_locked(struct fuse_conn *fc,
    > + struct inode *inode, u64 dmap_start)
    > +{
    > + int ret;
    > + struct fuse_inode *fi = get_fuse_inode(inode);
    > + struct fuse_dax_mapping *dmap;
    > +
    > + /* Find fuse dax mapping at file offset inode. */
    > + dmap = fuse_dax_interval_tree_iter_first(&fi->dmap_tree, dmap_start,
    > + dmap_start);
    > +
    > + /* Range already got cleaned up by somebody else */
    > + if (!dmap)
    > + return 0;
    > +
    > + /* still in use. */
    > + if (refcount_read(&dmap->refcnt) > 1)
    > + return 0;
    > +
    > + ret = reclaim_one_dmap_locked(fc, inode, dmap);
    > + if (ret < 0)
    > + return ret;
    > +
    > + /* Cleanup dmap entry and add back to free list */
    > + spin_lock(&fc->lock);
    > + dmap_reinit_add_to_free_pool(fc, dmap);
    > + spin_unlock(&fc->lock);
    > + return ret;
    > +}
    > +
    > +/*
    > + * Free a range of memory.
    > + * Locking.
    > + * 1. Take fuse_inode->i_mmap_sem to block dax faults.
    > + * 2. Take fuse_inode->i_dmap_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 *fc, struct inode *inode,
    > + u64 dmap_start, u64 dmap_end)
    > +{
    > + int ret;
    > + struct fuse_inode *fi = get_fuse_inode(inode);
    > +
    > + down_write(&fi->i_mmap_sem);
    > + ret = fuse_break_dax_layouts(inode, dmap_start, dmap_end);
    > + if (ret) {
    > + printk("virtio_fs: fuse_break_dax_layouts() failed. err=%d\n",
    > + ret);
    > + goto out_mmap_sem;
    > + }
    > +
    > + down_write(&fi->i_dmap_sem);
    > + ret = lookup_and_reclaim_dmap_locked(fc, inode, dmap_start);
    > + up_write(&fi->i_dmap_sem);
    > +out_mmap_sem:
    > + up_write(&fi->i_mmap_sem);
    > + return ret;
    > +}
    > +
    > +static int try_to_free_dmap_chunks(struct fuse_conn *fc,
    > + unsigned long nr_to_free)
    > +{
    > + struct fuse_dax_mapping *dmap, *pos, *temp;
    > + int ret, nr_freed = 0;
    > + u64 dmap_start = 0, window_offset = 0, dmap_end = 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(&fc->lock);
    > +
    > + if (!fc->nr_busy_ranges) {
    > + spin_unlock(&fc->lock);
    > + return 0;
    > + }
    > +
    > + list_for_each_entry_safe(pos, temp, &fc->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, &fc->busy_ranges);
    > + dmap_start = dmap->start;
    > + dmap_end = dmap->end;
    > + window_offset = dmap->window_offset;
    > + break;
    > + }
    > + spin_unlock(&fc->lock);
    > + if (!dmap)
    > + return 0;
    > +
    > + ret = lookup_and_reclaim_dmap(fc, inode, dmap_start, dmap_end);
    > + iput(inode);
    > + if (ret) {
    > + printk("%s(window_offset=0x%llx) failed. err=%d\n",
    > + __func__, window_offset, ret);
    > + return ret;
    > + }
    > + nr_freed++;
    > + }
    > + return 0;
    > +}
    > +
    > +void fuse_dax_free_mem_worker(struct work_struct *work)
    > +{
    > + int ret;
    > + struct fuse_conn *fc = container_of(work, struct fuse_conn,
    > + dax_free_work.work);
    > + pr_debug("fuse: Worker to free memory called. nr_free_ranges=%lu"
    > + " nr_busy_ranges=%lu\n", fc->nr_free_ranges,
    > + fc->nr_busy_ranges);
    > +
    > + ret = try_to_free_dmap_chunks(fc, 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(fc, 1);
    > +}
    > diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
    > index de213a7e1b0e..41c2fbff0d37 100644
    > --- a/fs/fuse/fuse_i.h
    > +++ b/fs/fuse/fuse_i.h
    > @@ -54,6 +54,16 @@
    > #define FUSE_DAX_MEM_RANGE_SZ (2*1024*1024)
    > #define FUSE_DAX_MEM_RANGE_PAGES (FUSE_DAX_MEM_RANGE_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)
    > +
    > /** List of active connections */
    > extern struct list_head fuse_conn_list;
    >
    > @@ -75,6 +85,9 @@ struct fuse_forget_link {
    >
    > /** 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 fc->free_ranges to keep track of free memory */
    > struct list_head list;
    >
    > @@ -97,6 +110,9 @@ struct fuse_dax_mapping {
    >
    > /* Is this mapping read-only or read-write */
    > bool writable;
    > +
    > + /* reference count when the mapping is used by dax iomap. */
    > + refcount_t refcnt;
    > };
    >
    > /** FUSE inode */
    > @@ -822,11 +838,19 @@ struct fuse_conn {
    > unsigned long nr_busy_ranges;
    > struct list_head busy_ranges;
    >
    > + /* Worker to free up memory ranges */
    > + struct delayed_work dax_free_work;
    > +
    > + /* Wait queue for a dax range to become free */
    > + wait_queue_head_t dax_range_waitq;
    > +
    > /*
    > * DAX Window Free Ranges
    > */
    > long nr_free_ranges;
    > struct list_head free_ranges;
    > +
    > + unsigned long nr_ranges;
    > };
    >
    > static inline struct fuse_conn *get_fuse_conn_super(struct super_block *sb)
    > @@ -1164,6 +1188,7 @@ unsigned int fuse_len_args(unsigned int numargs, struct fuse_arg *args);
    > */
    > u64 fuse_get_unique(struct fuse_iqueue *fiq);
    > void fuse_free_conn(struct fuse_conn *fc);
    > +void fuse_dax_free_mem_worker(struct work_struct *work);
    > void fuse_cleanup_inode_mappings(struct inode *inode);
    >
    > #endif /* _FS_FUSE_I_H */
    > diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
    > index d4770e7fb7eb..3560b62077a7 100644
    > --- a/fs/fuse/inode.c
    > +++ b/fs/fuse/inode.c
    > @@ -663,11 +663,13 @@ static int fuse_dax_mem_range_init(struct fuse_conn *fc,
    > range->window_offset = i * FUSE_DAX_MEM_RANGE_SZ;
    > range->length = FUSE_DAX_MEM_RANGE_SZ;
    > INIT_LIST_HEAD(&range->busy_list);
    > + refcount_set(&range->refcnt, 1);
    > list_add_tail(&range->list, &mem_ranges);
    > }
    >
    > list_replace_init(&mem_ranges, &fc->free_ranges);
    > fc->nr_free_ranges = nr_ranges;
    > + fc->nr_ranges = nr_ranges;
    > return 0;
    > out_err:
    > /* Free All allocated elements */
    > @@ -692,6 +694,7 @@ void fuse_conn_init(struct fuse_conn *fc, struct user_namespace *user_ns,
    > refcount_set(&fc->count, 1);
    > atomic_set(&fc->dev_count, 1);
    > init_waitqueue_head(&fc->blocked_waitq);
    > + init_waitqueue_head(&fc->dax_range_waitq);
    > fuse_iqueue_init(&fc->iq, fiq_ops, fiq_priv);
    > INIT_LIST_HEAD(&fc->bg_queue);
    > INIT_LIST_HEAD(&fc->entry);
    > @@ -711,6 +714,7 @@ void fuse_conn_init(struct fuse_conn *fc, struct user_namespace *user_ns,
    > fc->max_pages = FUSE_DEFAULT_MAX_PAGES_PER_REQ;
    > INIT_LIST_HEAD(&fc->free_ranges);
    > INIT_LIST_HEAD(&fc->busy_ranges);
    > + INIT_DELAYED_WORK(&fc->dax_free_work, fuse_dax_free_mem_worker);
    > }
    > EXPORT_SYMBOL_GPL(fuse_conn_init);
    >
    > @@ -719,6 +723,7 @@ void fuse_conn_put(struct fuse_conn *fc)
    > if (refcount_dec_and_test(&fc->count)) {
    > struct fuse_iqueue *fiq = &fc->iq;
    >
    > + flush_delayed_work(&fc->dax_free_work);
    > if (fc->dax_dev)
    > fuse_free_dax_mem_ranges(&fc->free_ranges);
    > if (fiq->ops->release)
    > --
    > 2.20.1

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