The patch titled
Subject: tmpfs: avoid a little creat and stat slowdown
has been added to the -mm tree. Its filename is
tmpfs-avoid-a-little-creat-and-stat-slowdown.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/tmpfs-avoid-a-little-creat-and-stat-slowdown.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/tmpfs-avoid-a-little-creat-and-stat-slowdown.patch
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From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: tmpfs: avoid a little creat and stat slowdown
LKP reports that v4.2 commit afa2db2fb6f1 ("tmpfs: truncate prealloc
blocks past i_size") causes a 14.5% slowdown in the AIM9 creat-clo
benchmark.
creat-clo does just what you'd expect from the name, and creat's O_TRUNC
on 0-length file does indeed get into more overhead now shmem_setattr()
tests "0 <= 0" instead of "0 < 0".
I'm not sure how much we care, but I think it would not be too VW-like to
add in a check for whether any pages (or swap) are allocated: if none are
allocated, there's none to remove from the radix_tree. At first I thought
that check would be good enough for the unmaps too, but no: we should not
skip the unlikely case of unmapping pages beyond the new EOF, which were
COWed from holes which have now been reclaimed, leaving none.
This gives me an 8.5% speedup: on Haswell instead of LKP's Westmere, and
running a debug config before and after: I hope those account for the
lesser speedup.
And probably someone has a benchmark where a thousand threads keep on
stat'ing the same file repeatedly: forestall that report by adjusting v4.3
commit 44a30220bc0a ("shmem: recalculate file inode when fstat") not to
take the spinlock in shmem_getattr() when there's no work to do.
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Reported-by: Ying Huang <ying.huang@xxxxxxxxxxxxxxx>
Tested-by: Ying Huang <ying.huang@xxxxxxxxxxxxxxx>
Cc: Josef Bacik <jbacik@xxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 22 ++++++++++++++--------
1 file changed, 14 insertions(+), 8 deletions(-)
diff -puN mm/shmem.c~tmpfs-avoid-a-little-creat-and-stat-slowdown mm/shmem.c
--- a/mm/shmem.c~tmpfs-avoid-a-little-creat-and-stat-slowdown
+++ a/mm/shmem.c
@@ -550,12 +550,12 @@ static int shmem_getattr(struct vfsmount
struct inode *inode = dentry->d_inode;
struct shmem_inode_info *info = SHMEM_I(inode);
- spin_lock(&info->lock);
- shmem_recalc_inode(inode);
- spin_unlock(&info->lock);
-
+ if (info->alloced - info->swapped != inode->i_mapping->nrpages) {
+ spin_lock(&info->lock);
+ shmem_recalc_inode(inode);
+ spin_unlock(&info->lock);
+ }
generic_fillattr(inode, stat);
-
return 0;
}
@@ -588,10 +588,16 @@ static int shmem_setattr(struct dentry *
}
if (newsize <= oldsize) {
loff_t holebegin = round_up(newsize, PAGE_SIZE);
- unmap_mapping_range(inode->i_mapping, holebegin, 0, 1);
- shmem_truncate_range(inode, newsize, (loff_t)-1);
+ if (oldsize > holebegin)
+ unmap_mapping_range(inode->i_mapping,
+ holebegin, 0, 1);
+ if (info->alloced)
+ shmem_truncate_range(inode,
+ newsize, (loff_t)-1);
/* unmap again to remove racily COWed private pages */
- unmap_mapping_range(inode->i_mapping, holebegin, 0, 1);
+ if (oldsize > holebegin)
+ unmap_mapping_range(inode->i_mapping,
+ holebegin, 0, 1);
}
}
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
memcg-simplify-and-inline-__mem_cgroup_from_kmem-fix-2.patch
mm-documentation-undoc-non-linear-vmas.patch
mm-rmap-use-pte-lock-not-mmap_sem-to-set-pagemlocked.patch
mm-page-migration-fix-pagemlocked-on-migrated-pages.patch
mm-rename-mem_cgroup_migrate-to-mem_cgroup_replace_page.patch
mm-correct-a-couple-of-page-migration-comments.patch
mm-page-migration-use-the-put_new_page-whenever-necessary.patch
mm-page-migration-trylock-newpage-at-same-level-as-oldpage.patch
mm-page-migration-remove_migration_ptes-at-lockunlock-level.patch
mm-simplify-page-migrations-anon_vma-comment-and-flow.patch
mm-page-migration-use-migration-entry-for-swapcache-too.patch
mm-page-migration-avoid-touching-newpage-until-no-going-back.patch
mm-migrate-dirty-page-without-clear_page_dirty_for_io-etc.patch
tmpfs-avoid-a-little-creat-and-stat-slowdown.patch
mm-use-unsigned-int-for-page-order-fix-2.patch
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