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Btrfs: fix very slow inode eviction and fs unmount

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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@gmail.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>
This commit is contained in:
Filipe David Borba Manana 2013-11-19 22:29:35 +00:00 committed by Chris Mason
parent 0647bf564f
commit 131e404a2a
1 changed files with 84 additions and 14 deletions
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82
fs/btrfs/inode.c
View file

@ -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;
}
if (!inode_evicting)
lock_extent_bits(tree, page_start, page_end, 0, &cached_state);
ordered = btrfs_lookup_ordered_extent(inode, page_offset(page));
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
*/
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);
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);
if (!inode_evicting) {
cached_state = NULL;
lock_extent_bits(tree, page_start, page_end, 0, &cached_state);
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,
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)) {