On Thu, Dec 08, 2011 at 02:59:54PM +0800, Robin Dong wrote: > 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> Thanks, applied. - Ted -- 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
