All of lore.kernel.org
 help / color / mirror / Atom feed
From: Christoph Hellwig <hch@lst.de>
To: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@lst.de>, linux-xfs@vger.kernel.org
Subject: Re: [PATCH 08/11] xfs: centralize page allocation and freeing for buffers
Date: Thu, 20 May 2021 07:35:04 +0200	[thread overview]
Message-ID: <20210520053504.GA21318@lst.de> (raw)
In-Reply-To: <20210519232245.GG664593@dread.disaster.area>

On Thu, May 20, 2021 at 09:22:45AM +1000, Dave Chinner wrote:
> 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.

It makes a whole lot of sense, but it seems you don't like the
structure :)

As stated in the commit log we now have one helper that sets a
_XBF_PAGES backing with pages and the map, and one helper to
tear it down.   I think it makes a whole lot of sense this way.

> 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.

It is something we also do elsewhere in the kernel.  Another
alternative would be to do a NULL check on the page, or to just
pointlessly duplicate the freeing loop.

> 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.

This is to clearly split code consolidatation from behavior changes.
I could move both earlier at the downside of adding a lot of new
code first that later gets removed.

> 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....

As mentioned in the cover letter: the bulk allocation review is what
trigger this as it tripped me following various lose ends.  And as
usual I'd rather have that kind of change at the end where the
surrounding code makes sense, so the rebased version is now is patch 11
of this series.

  reply	other threads:[~2021-05-20  5:35 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
2021-05-20  5:35     ` Christoph Hellwig [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210520053504.GA21318@lst.de \
    --to=hch@lst.de \
    --cc=david@fromorbit.com \
    --cc=linux-xfs@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.