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From: Dave Chinner <david@fromorbit.com>
To: Christoph Hellwig <hch@lst.de>
Cc: linux-xfs@vger.kernel.org
Subject: Re: [PATCH 08/11] xfs: centralize page allocation and freeing for buffers
Date: Thu, 20 May 2021 09:22:45 +1000	[thread overview]
Message-ID: <20210519232245.GG664593@dread.disaster.area> (raw)
In-Reply-To: <20210519190900.320044-9-hch@lst.de>

On Wed, May 19, 2021 at 09:08:57PM +0200, Christoph Hellwig wrote:
> Factor out two helpers that do everything needed for allocating and
> freeing pages that back a buffer, and remove the duplication between
> the different interfaces.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

This seems really confused.

Up until this point in the patch set you are pulling code out
of xfs_buf_alloc_pages() into helpers. Now you are getting rid of
the helpers and putting the slightly modified code back into
xfs_buf_alloc_pages(). This doesn't make any sense at all.

The freeing helper now requires the buffer state to be
manipulated on allocation failure so that the free function doesn't
run off the end of the bp->b_pages array. That's a bit of a
landmine, and it doesn't really clean anything up much at all.

And on the allocation side there is new "fail fast" behaviour
because you've lifted the readahead out of xfs_buf_alloc_pages. You
also lifted the zeroing checks, which I note that you immediately
put back inside xfs_buf_alloc_pages() in the next patch.

The stuff up to this point in the series makes sense. From this
patch onwards it seems to me that you're just undoing the factoring
and cleanups from the first few patches...

I mean, like the factoring of xfs_buf_alloc_slab(), you could have
just factored out xfs_buf_alloc_pages(bp, page_count) from
xfs_buf_allocate_memory() and used that directly in
xfs_buf_get_uncached() and avoided a bunch of this factoring, make a
slight logic modification and recombine churn. And it would be
trivial to do on top of the bulk allocation patch which already
converts both of these functions to use bulk allocation....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

  reply	other threads:[~2021-05-19 23:22 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-19 19:08 RFC: buffer cache backing page allocation cleanup Christoph Hellwig
2021-05-19 19:08 ` [PATCH 01/11] xfs: cleanup error handling in xfs_buf_get_map Christoph Hellwig
2021-05-20 23:43   ` Darrick J. Wong
2021-05-19 19:08 ` [PATCH 02/11] xfs: split xfs_buf_allocate_memory Christoph Hellwig
2021-05-19 22:36   ` Dave Chinner
2021-05-19 19:08 ` [PATCH 03/11] xfs: remove ->b_offset handling for page backed buffers Christoph Hellwig
2021-05-19 22:27   ` Dave Chinner
2021-05-19 19:08 ` [PATCH 04/11] xfs: cleanup _xfs_buf_get_pages Christoph Hellwig
2021-05-19 22:40   ` Dave Chinner
2021-05-20  5:23     ` Christoph Hellwig
2021-05-25 22:43       ` Dave Chinner
2021-05-19 19:08 ` [PATCH 05/11] xfs: remove the xb_page_found stat counter in xfs_buf_alloc_pages Christoph Hellwig
2021-05-19 22:55   ` Dave Chinner
2021-05-19 19:08 ` [PATCH 06/11] xfs: remove the size and nbytes variables " Christoph Hellwig
2021-05-19 22:56   ` Dave Chinner
2021-05-19 19:08 ` [PATCH 07/11] xfs: simplify the b_page_count calculation Christoph Hellwig
2021-05-19 19:08 ` [PATCH 08/11] xfs: centralize page allocation and freeing for buffers Christoph Hellwig
2021-05-19 23:22   ` Dave Chinner [this message]
2021-05-20  5:35     ` Christoph Hellwig
2021-05-25 23:59       ` Dave Chinner
2021-05-19 19:08 ` [PATCH 09/11] xfs: lift the buffer zeroing logic into xfs_buf_alloc_pages Christoph Hellwig
2021-05-19 19:08 ` [PATCH 10/11] xfs: retry allocations from xfs_buf_get_uncached as well Christoph Hellwig
2021-05-19 19:09 ` [PATCH 11/11] xfs: use alloc_pages_bulk_array() for buffers Christoph Hellwig

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