linux-ext4 - Re: [PATCH v2] ext4: directly leave out of ext4_find_delalloc_range() if filesystem mount with "nodelalloc"

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Message-ID: <CAGBYx2Y0hHX4D-AKxvgTpMmPnxYCGrbd2dODZAeiOwnaOFLOeQ@mail.gmail.com>
Date:	Thu, 8 Dec 2011 16:36:53 +0800
From:	Yongqiang Yang <xiaoqiangnk@...il.com>
To:	Robin Dong <sanbai@...bao.com>
Cc:	linux-ext4@...r.kernel.org, "Ted Ts'o" <tytso@....edu>
Subject: Re: [PATCH v2] ext4: directly leave out of ext4_find_delalloc_range()
 if filesystem mount with "nodelalloc"

On Thu, Dec 8, 2011 at 2:59 PM, Robin Dong <hao.bigrat@...il.com> wrote:
> From: Robin Dong <sanbai@...bao.com>
>
> 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@...bao.com>
> ---
>  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
>
> --
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-- 
Best Wishes
Yongqiang Yang
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