From: Robin Dong <sanbai@xxxxxxxxxx> We found performance regression when using bigalloc with "nodelalloc" (1MB cluster size): 1. mke2fs -C 1048576 -O ^has_journal,bigalloc /dev/sda 2. mount -o nodelalloc /dev/sda /test/ 3. time dd if=/dev/zero of=/test/io bs=1048576 count=1024 The "dd" will cost about 2 seconds to finish, but if we mke2fs without "bigalloc", "dd" will only cost lesss than 1 second. The reason is: when using ext4 with "nodelalloc", it will call ext4_find_delalloc_cluster() nearly everytime it call ext4_ext_map_blocks(), and ext4_find_delalloc_range() will also scan all pages in cluster because no buffer is "delayed". A cluster has 256 pages (1MB cluster), so it will scan 256 * 256k pags when creating a 1G file. That severely hurts the performance. Therefore, we return out from ext4_find_delalloc_range() when using "nodelalloc". Signed-off-by: Robin Dong <sanbai@xxxxxxxxxx> --- fs/ext4/extents.c | 3 +++ 1 files changed, 3 insertions(+), 0 deletions(-) diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index 61fa9e1..60f5f25 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -3282,6 +3282,9 @@ static int ext4_find_delalloc_range(struct inode *inode, ext4_lblk_t i, pg_lblk; pgoff_t index; + if (!test_opt(inode->i_sb, DELALLOC)) + return 0; + /* reverse search wont work if fs block size is less than page size */ if (inode->i_blkbits < PAGE_CACHE_SHIFT) search_hint_reverse = 0; -- 1.7.4.1 -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
