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Re: [PATCH] xfs: improve xfs_iext_destroy() by freeing extent indirectio

To: Jeff Liu <jeff.liu@xxxxxxxxxx>
Subject: Re: [PATCH] xfs: improve xfs_iext_destroy() by freeing extent indirection array directly
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Mon, 23 Sep 2013 10:36:18 +1000
Cc: "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <523C5E92.8000406@xxxxxxxxxx>
References: <523C5E92.8000406@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Fri, Sep 20, 2013 at 10:41:22PM +0800, Jeff Liu wrote:
> From: Jie Liu <jeff.liu@xxxxxxxxxx>
> 
> To free the incore file extents stores at the indirection array, we
> call the common routine xfs_iext_irec_remove() to remove a record
> from the array one at a time in reverse order, which will resize an
> extent indirection array repeatedly according to the array size.
> 
> This is not often the case to make a file with thousands extent records
> stores at an indirection array, but above operation is inefficient and
> could result in memory fragments.

Yes, it may be inefficient, but I don't see that it's a contributor
to memory fragmentation as the reallocated buffer is freed shortly
after it has been allocated as the array shrinks. Do you have any
evidence to suggest that such behaviour is actually fragmenting
memory? If so, is the any test case that reproduces this problem?

How did you test the change?

> This patch refine xfs_iext_destroy() by freeing the extent records from
> the indirection array directly in this case.
> 
> Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>
> ---

FWIW, it is best to title a resend as [PATCH x/y, V2], and here tell
us what changed between posts such as:

V2:
- fixed typo in original posting

>  fs/xfs/xfs_inode_fork.c |    7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/xfs_inode_fork.c b/fs/xfs/xfs_inode_fork.c
> index 02f1083..ba70f98 100644
> --- a/fs/xfs/xfs_inode_fork.c
> +++ b/fs/xfs/xfs_inode_fork.c
> @@ -1525,9 +1525,12 @@ xfs_iext_destroy(
>               int     nlists;
>  
>               nlists = ifp->if_real_bytes / XFS_IEXT_BUFSZ;
> -             for (erp_idx = nlists - 1; erp_idx >= 0 ; erp_idx--) {
> -                     xfs_iext_irec_remove(ifp, erp_idx);
> +             for (erp_idx = 0; erp_idx < nlists; erp_idx++) {
> +                     xfs_ext_irec_t  *erp = &ifp->if_u1.if_ext_irec[erp_idx];
> +                     if (erp->er_extbuf)
> +                             kmem_free(erp->er_extbuf);
>               }
> +             kmem_free(ifp->if_u1.if_ext_irec);


The code looks correct...

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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