linux-ext4 - Re: [PATCH] Ext4: Don't normalize an falloc request if it can fit in 1 extent.

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Date:	Fri, 28 Oct 2011 12:47:17 -0600
From:	Andreas Dilger <aedilger@...il.com>
To:	Greg Harm <gharm@...gle.com>
Cc:	Theodore Ts'o <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	Greg Harm <gharm@...gle.com>
Subject: Re: [PATCH] Ext4: Don't normalize an falloc request if it can fit in 1 extent.

On 2011-10-28, at 12:01 PM, Greg Harm <gharm@...gle.com> wrote:
> If an fallocate request fits in EXT_UNINIT_MAX_LEN, then set the
> EXT4_GET_BLOCKS_NO_NORMALIZE flag. For larger fallocate requests,
> let mballoc.c normalize the request.
> This fixes a problem where large requests were being split
> into non-contiguous extents due to haldar@...gle.com's
> "ext4: do not normalize block requests from fallocate."
> 
> Testing: Checked that 8.x MB falloc'ed files are still laid down
> next to each other (contiguously).
> Checked that the maximum size extent (127.9MB) is allocated as 1
> extent.
> Checked that a 1GB file is somewhat contiguous (often 5-6
> non-contiguous extents now).
> Checked that a 120MB file can still be falloc'ed even if there are no
> single extents large enough to hold it.

It would be great to add these test cases to xfstests so that this doesn't break in the future. 

> Signed-off-by: Greg Harm <gharm@...gle.com>
> ---
> fs/ext4/extents.c |   13 ++++++++++---
> 1 files changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 57cf568..9819216 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -3761,6 +3761,7 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
>    int ret2 = 0;
>    int retries = 0;
>    struct ext4_map_blocks map;
> +    int map_blocks_flags;
>    unsigned int credits, blkbits = inode->i_blkbits;
> 
>    /*
> @@ -3805,9 +3806,15 @@ retry:
>            ret = PTR_ERR(handle);
>            break;
>        }
> -        ret = ext4_map_blocks(handle, inode, &map,
> -                      EXT4_GET_BLOCKS_CREATE_UNINIT_EXT |
> -                      EXT4_GET_BLOCKS_NO_NORMALIZE);
> +        map_blocks_flags = EXT4_GET_BLOCKS_CREATE_UNINIT_EXT;
> +        /*
> +         * Don't normalize the request if it can fit in one extent so
> +         * that it doesn't get unnecessarily split into multiple
> +         * extents.
> +         */
> +        if (len <= EXT_UNINIT_MAX_LEN << blkbits)
> +            map_blocks_flags |= EXT4_GET_BLOCKS_NO_NORMALIZE;
> +        ret = ext4_map_blocks(handle, inode, &map, map_blocks_flags);
>        if (ret <= 0) {
> #ifdef EXT4FS_DEBUG
>            WARN_ON(ret <= 0);
> -- 
> 1.7.3.1
> 
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