The inode eviction can be very slow, because during eviction we
tell the VFS to truncate all of the inode's pages. This results
in calls to btrfs_invalidatepage() which in turn does calls to
lock_extent_bits() and clear_extent_bit(). These calls result in
too many merges and splits of extent_state structures, which
consume a lot of time and cpu when the inode has many pages. In
some scenarios I have experienced umount times higher than 15
minutes, even when there's no pending IO (after a btrfs fs sync).
A quick way to reproduce this issue:
$ mkfs.btrfs -f /dev/sdb3
$ mount /dev/sdb3 /mnt/btrfs
$ cd /mnt/btrfs
$ sysbench --test=fileio --file-num=128 --file-total-size=16G \
--file-test-mode=seqwr --num-threads=128 \
--file-block-size=16384 --max-time=60 --max-requests=0 run
$ time btrfs fi sync .
FSSync '.'
real 0m25.457s
user 0m0.000s
sys 0m0.092s
$ cd ..
$ time umount /mnt/btrfs
real 1m38.234s
user 0m0.000s
sys 1m25.760s
The same test on ext4 runs much faster:
$ mkfs.ext4 /dev/sdb3
$ mount /dev/sdb3 /mnt/ext4
$ cd /mnt/ext4
$ sysbench --test=fileio --file-num=128 --file-total-size=16G \
--file-test-mode=seqwr --num-threads=128 \
--file-block-size=16384 --max-time=60 --max-requests=0 run
$ sync
$ cd ..
$ time umount /mnt/ext4
real 0m3.626s
user 0m0.004s
sys 0m3.012s
After this patch, the unmount (inode evictions) is much faster:
$ mkfs.btrfs -f /dev/sdb3
$ mount /dev/sdb3 /mnt/btrfs
$ cd /mnt/btrfs
$ sysbench --test=fileio --file-num=128 --file-total-size=16G \
--file-test-mode=seqwr --num-threads=128 \
--file-block-size=16384 --max-time=60 --max-requests=0 run
$ time btrfs fi sync .
FSSync '.'
real 0m26.774s
user 0m0.000s
sys 0m0.084s
$ cd ..
$ time umount /mnt/btrfs
real 0m1.811s
user 0m0.000s
sys 0m1.564s
Signed-off-by: Filipe David Borba Manana <fdmanana@xxxxxxxxx>
---
fs/btrfs/inode.c | 98 ++++++++++++++++++++++++++++++++++++++++++++++--------
1 file changed, 84 insertions(+), 14 deletions(-)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 5a5de36..e889779 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -4488,6 +4488,62 @@ static int btrfs_setattr(struct dentry *dentry, struct iattr *attr)
return err;
}
+/*
+ * While truncating the inode pages during eviction, we get the VFS calling
+ * btrfs_invalidatepage() against each page of the inode. This is slow because
+ * the calls to btrfs_invalidatepage() result in a huge amount of calls to
+ * lock_extent_bits() and clear_extent_bit(), which keep merging and splitting
+ * extent_state structures over and over, wasting lots of time.
+ *
+ * Therefore if the inode is being evicted, let btrfs_invalidatepage() skip all
+ * those expensive operations on a per page basis and do only the ordered io
+ * finishing, while we release here the extent_map and extent_state structures,
+ * without the excessive merging and splitting.
+ */
+static void evict_inode_truncate_pages(struct inode *inode)
+{
+ struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
+ struct extent_map_tree *map_tree = &BTRFS_I(inode)->extent_tree;
+ struct rb_node *node;
+
+ ASSERT(inode->i_state & I_FREEING);
+ truncate_inode_pages(&inode->i_data, 0);
+
+ write_lock(&map_tree->lock);
+ while (!RB_EMPTY_ROOT(&map_tree->map)) {
+ struct extent_map *em;
+
+ node = rb_first(&map_tree->map);
+ em = rb_entry(node, struct extent_map, rb_node);
+ remove_extent_mapping(map_tree, em);
+ free_extent_map(em);
+ }
+ write_unlock(&map_tree->lock);
+
+ spin_lock(&io_tree->lock);
+ while (!RB_EMPTY_ROOT(&io_tree->state)) {
+ struct extent_state *state;
+ struct extent_state *cached_state = NULL;
+
+ node = rb_first(&io_tree->state);
+ state = rb_entry(node, struct extent_state, rb_node);
+ atomic_inc(&state->refs);
+ spin_unlock(&io_tree->lock);
+
+ lock_extent_bits(io_tree, state->start, state->end,
+ 0, &cached_state);
+ clear_extent_bit(io_tree, state->start, state->end,
+ EXTENT_LOCKED | EXTENT_DIRTY |
+ EXTENT_DELALLOC | EXTENT_DO_ACCOUNTING |
+ EXTENT_DEFRAG, 1, 1,
+ &cached_state, GFP_NOFS);
+ free_extent_state(state);
+
+ spin_lock(&io_tree->lock);
+ }
+ spin_unlock(&io_tree->lock);
+}
+
void btrfs_evict_inode(struct inode *inode)
{
struct btrfs_trans_handle *trans;
@@ -4498,7 +4554,8 @@ void btrfs_evict_inode(struct inode *inode)
trace_btrfs_inode_evict(inode);
- truncate_inode_pages(&inode->i_data, 0);
+ evict_inode_truncate_pages(inode);
+
if (inode->i_nlink &&
((btrfs_root_refs(&root->root_item) != 0 &&
root->root_key.objectid != BTRFS_ROOT_TREE_OBJECTID) ||
@@ -7379,6 +7436,7 @@ static void btrfs_invalidatepage(struct page *page, unsigned int offset,
struct extent_state *cached_state = NULL;
u64 page_start = page_offset(page);
u64 page_end = page_start + PAGE_CACHE_SIZE - 1;
+ int inode_evicting = inode->i_state & I_FREEING;
/*
* we have the page locked, so new writeback can't start,
@@ -7394,17 +7452,21 @@ static void btrfs_invalidatepage(struct page *page, unsigned int offset,
btrfs_releasepage(page, GFP_NOFS);
return;
}
- lock_extent_bits(tree, page_start, page_end, 0, &cached_state);
- ordered = btrfs_lookup_ordered_extent(inode, page_offset(page));
+
+ if (!inode_evicting)
+ lock_extent_bits(tree, page_start, page_end, 0, &cached_state);
+ ordered = btrfs_lookup_ordered_extent(inode, page_start);
if (ordered) {
/*
* IO on this page will never be started, so we need
* to account for any ordered extents now
*/
- clear_extent_bit(tree, page_start, page_end,
- EXTENT_DIRTY | EXTENT_DELALLOC |
- EXTENT_LOCKED | EXTENT_DO_ACCOUNTING |
- EXTENT_DEFRAG, 1, 0, &cached_state, GFP_NOFS);
+ if (!inode_evicting)
+ clear_extent_bit(tree, page_start, page_end,
+ EXTENT_DIRTY | EXTENT_DELALLOC |
+ EXTENT_LOCKED | EXTENT_DO_ACCOUNTING |
+ EXTENT_DEFRAG, 1, 0, &cached_state,
+ GFP_NOFS);
/*
* whoever cleared the private bit is responsible
* for the finish_ordered_io
@@ -7428,14 +7490,22 @@ static void btrfs_invalidatepage(struct page *page, unsigned int offset,
btrfs_finish_ordered_io(ordered);
}
btrfs_put_ordered_extent(ordered);
- cached_state = NULL;
- lock_extent_bits(tree, page_start, page_end, 0, &cached_state);
+ if (!inode_evicting) {
+ cached_state = NULL;
+ lock_extent_bits(tree, page_start, page_end, 0,
+ &cached_state);
+ }
+ }
+
+ if (!inode_evicting) {
+ clear_extent_bit(tree, page_start, page_end,
+ EXTENT_LOCKED | EXTENT_DIRTY |
+ EXTENT_DELALLOC | EXTENT_DO_ACCOUNTING |
+ EXTENT_DEFRAG, 1, 1,
+ &cached_state, GFP_NOFS);
+
+ __btrfs_releasepage(page, GFP_NOFS);
}
- clear_extent_bit(tree, page_start, page_end,
- EXTENT_LOCKED | EXTENT_DIRTY | EXTENT_DELALLOC |
- EXTENT_DO_ACCOUNTING | EXTENT_DEFRAG, 1, 1,
- &cached_state, GFP_NOFS);
- __btrfs_releasepage(page, GFP_NOFS);
ClearPageChecked(page);
if (PagePrivate(page)) {
--
1.7.9.5
--
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