From: Robin Dong Date: Mon, 19 Dec 2011 04:05:43 +0000 (-0500) Subject: ext4: optimize ext4_find_delalloc_range() in nodelalloc mode X-Git-Tag: v3.3-rc1~114^2^2~27 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8c48f7e88e293b9dd422bd8884842aea85d30b22;p=pandora-kernel.git ext4: optimize ext4_find_delalloc_range() in nodelalloc mode 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 less 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 immediately from ext4_find_delalloc_range() in nodelalloc mode, since by definition there can't be any delalloc pages. Signed-off-by: Robin Dong Signed-off-by: "Theodore Ts'o" --- Reading git-diff-tree failed