On Mon, Dec 16, 2013 at 11:05:31AM +0000, Filipe David Manana wrote:
> On Mon, Dec 16, 2013 at 9:27 AM, Liu Bo <bo.li.liu@xxxxxxxxxx> wrote:
> > On Tue, Nov 19, 2013 at 10:29:35PM +0000, Filipe David Borba Manana wrote:
> >> 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
> >>
> >
> > What about the time of umount after 'sync'?
>
> Same huge difference.
> Thanks.
Not seeing that huge one with the latest btrfs, maybe because your memory is
rather larger.
time sync
FSSync '/mnt/btrfs'
real 0m17.006s
user 0m0.004s
sys 0m0.056s
time umount /mnt/btrfs
real 0m0.910s
user 0m0.003s
sys 0m0.715s
-liubo
>
> >
> > The following ext4 uses sync while btrfs uses 'btrfs filesystem sync'.
> >
> > I don't think they are the same thing.
> >
> > -liubo
> >
> >> 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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>
>
>
> --
> Filipe David Manana,
>
> "Reasonable men adapt themselves to the world.
> Unreasonable men adapt the world to themselves.
> That's why all progress depends on unreasonable men."
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