linux-kernel - Re: [PATCH v4 04/14] xfs: make EOF allocation simpler

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Message-ID: <87ed5z2s5a.fsf@gmail.com>
Date: Wed, 04 Sep 2024 23:55:05 +0530
From: Ritesh Harjani (IBM) <ritesh.list@...il.com>
To: John Garry <john.g.garry@...cle.com>, chandan.babu@...cle.com, djwong@...nel.org, dchinner@...hat.com, hch@....de
Cc: viro@...iv.linux.org.uk, brauner@...nel.org, jack@...e.cz, linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, catherine.hoang@...cle.com, martin.petersen@...cle.com, John Garry <john.g.garry@...cle.com>
Subject: Re: [PATCH v4 04/14] xfs: make EOF allocation simpler

John Garry <john.g.garry@...cle.com> writes:

> From: Dave Chinner <dchinner@...hat.com>
>
> Currently the allocation at EOF is broken into two cases - when the
> offset is zero and when the offset is non-zero. When the offset is
> non-zero, we try to do exact block allocation for contiguous
> extent allocation. When the offset is zero, the allocation is simply
> an aligned allocation.
>
> We want aligned allocation as the fallback when exact block
> allocation fails, but that complicates the EOF allocation in that it
> now has to handle two different allocation cases. The
> caller also has to handle allocation when not at EOF, and for the
> upcoming forced alignment changes we need that to also be aligned
> allocation.
>
> To simplify all this, pull the aligned allocation cases back into
> the callers and leave the EOF allocation path for exact block
> allocation only. This means that the EOF exact block allocation
> fallback path is the normal aligned allocation path and that ends up
> making things a lot simpler when forced alignment is introduced.
>
> Signed-off-by: Dave Chinner <dchinner@...hat.com>
> Reviewed-by: "Darrick J. Wong" <djwong@...nel.org>
> Signed-off-by: John Garry <john.g.garry@...cle.com>
> ---
>  fs/xfs/libxfs/xfs_bmap.c   | 129 +++++++++++++++----------------------
>  fs/xfs/libxfs/xfs_ialloc.c |   2 +-
>  2 files changed, 54 insertions(+), 77 deletions(-)
>
<..>

> diff --git a/fs/xfs/libxfs/xfs_ialloc.c b/fs/xfs/libxfs/xfs_ialloc.c
> index 2fa29d2f004e..c5d220d51757 100644
> --- a/fs/xfs/libxfs/xfs_ialloc.c
> +++ b/fs/xfs/libxfs/xfs_ialloc.c
> @@ -780,7 +780,7 @@ xfs_ialloc_ag_alloc(
>  		 * the exact agbno requirement and increase the alignment
>  		 * instead. It is critical that the total size of the request
>  		 * (len + alignment + slop) does not increase from this point
> -		 * on, so reset minalignslop to ensure it is not included in
> +		 * on, so reset alignslop to ensure it is not included in
>  		 * subsequent requests.
>  		 */
>  		args.alignslop = 0;

minor comment: Looks like this diff got leftover from previous patch
where we cleanup minalignslop/alignslop.

-ritesh