On Thu, Dec 8, 2011 at 2:59 PM, Robin Dong <hao.bigrat@xxxxxxxxx> 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. Looks good to me. I think delayed extent tree can help a lot when a cluster has hundreds of pages in delalloc case. Hi Ted, Any plans on merging delayed extent tree patches? Yongqiang. > > 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 -- Best Wishes Yongqiang Yang -- 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
