From: Jan Kara <jack@xxxxxxx>
Subject: fs: fix performance regression in clean_bdev_aliases()
e64855c6cfaa ("fs: Add helper to clean bdev aliases under a bh and use
it") added a wrapper for clean_bdev_aliases() that invalidates bdev
aliases underlying a single buffer head. However this has caused a
performance regression for bonnie++ benchmark on ext4 filesystem when
delayed allocation is turned off (ext3 mode) - average of 3 runs:
Hmean SeqOut Char 164787.55 ( 0.00%) 107189.06 (-34.95%)
Hmean SeqOut Block 219883.89 ( 0.00%) 168870.32 (-23.20%)
The reason for this regression is that clean_bdev_aliases() is slower
when called for a single block because pagevec_lookup() it uses will end
up iterating through the radix tree until it finds a page (which may
take a while) but we are only interested whether there's a page at a
particular index.
Fix the problem by using pagevec_lookup_range() instead which avoids the
needless iteration.
Fixes: e64855c6cfaa ("fs: Add helper to clean bdev aliases under a bh and use it")
Link: http://lkml.kernel.org/r/20170726114704.7626-5-jack@xxxxxxx
Signed-off-by: Jan Kara <jack@xxxxxxx>
Cc: Jens Axboe <axboe@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/buffer.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)
diff -puN fs/buffer.c~fs-fix-performance-regression-in-clean_bdev_aliases fs/buffer.c
--- a/fs/buffer.c~fs-fix-performance-regression-in-clean_bdev_aliases
+++ a/fs/buffer.c
@@ -1627,19 +1627,18 @@ void clean_bdev_aliases(struct block_dev
struct pagevec pvec;
pgoff_t index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
pgoff_t end;
- int i;
+ int i, count;
struct buffer_head *bh;
struct buffer_head *head;
end = (block + len - 1) >> (PAGE_SHIFT - bd_inode->i_blkbits);
pagevec_init(&pvec, 0);
- while (index <= end && pagevec_lookup(&pvec, bd_mapping, &index,
- min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) {
- for (i = 0; i < pagevec_count(&pvec); i++) {
+ while (pagevec_lookup_range(&pvec, bd_mapping, &index, end,
+ PAGEVEC_SIZE)) {
+ count = pagevec_count(&pvec);
+ for (i = 0; i < count; i++) {
struct page *page = pvec.pages[i];
- if (page->index > end)
- break;
if (!page_has_buffers(page))
continue;
/*
@@ -1669,6 +1668,9 @@ unlock_page:
}
pagevec_release(&pvec);
cond_resched();
+ /* End of range already reached? */
+ if (index > end || !index)
+ break;
}
}
EXPORT_SYMBOL(clean_bdev_aliases);
_
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