linux-fsdevel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Yafang Shao <laoar.shao@gmail.com>
To: Dave Chinner <david@fromorbit.com>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>,
	Matthew Wilcox <willy@infradead.org>,
	Christoph Hellwig <hch@infradead.org>,
	Michal Hocko <mhocko@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	David Howells <dhowells@redhat.com>,
	jlayton@redhat.com, linux-fsdevel@vger.kernel.org,
	linux-cachefs@redhat.com, linux-xfs@vger.kernel.org,
	Linux MM <linux-mm@kvack.org>, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v10 4/4] xfs: use current->journal_info to avoid transaction reservation recursion
Date: Tue, 8 Dec 2020 13:01:40 +0800	[thread overview]
Message-ID: <CALOAHbA8QtaxKx85U7UraU4D4MzjU=pR7rs0duVfPRvyarymSQ@mail.gmail.com> (raw)
In-Reply-To: <20201208042026.GW3913616@dread.disaster.area>

On Tue, Dec 8, 2020 at 12:20 PM Dave Chinner <david@fromorbit.com> wrote:
>
> On Tue, Dec 08, 2020 at 10:15:43AM +0800, Yafang Shao wrote:
> > PF_FSTRANS which is used to avoid transaction reservation recursion, is
> > dropped since commit 9070733b4efa ("xfs: abstract PF_FSTRANS to
> > PF_MEMALLOC_NOFS") and commit 7dea19f9ee63 ("mm: introduce
> > memalloc_nofs_{save,restore} API") and replaced by PF_MEMALLOC_NOFS which
> > means to avoid filesystem reclaim recursion.
> >
> > As these two flags have different meanings, we'd better reintroduce
> > PF_FSTRANS back. To avoid wasting the space of PF_* flags in task_struct,
> > we can reuse the current->journal_info to do that, per Willy. As the
> > check of transaction reservation recursion is used by XFS only, we can
> > move the check into xfs_vm_writepage(s), per Dave.
> >
> > To better abstract that behavoir, two new helpers are introduced, as
> > follows,
> > - xfs_trans_context_active
> >   To check whehter current is in fs transcation or not
> > - xfs_trans_context_swap
> >   Transfer the transaction context when rolling a permanent transaction
> >
> > These two new helpers are instroduced in xfs_trans.h.
> >
> > Cc: Darrick J. Wong <darrick.wong@oracle.com>
> > Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
> > Cc: Christoph Hellwig <hch@lst.de>
> > Cc: Dave Chinner <david@fromorbit.com>
> > Cc: Michal Hocko <mhocko@kernel.org>
> > Cc: David Howells <dhowells@redhat.com>
> > Cc: Jeff Layton <jlayton@redhat.com>
> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> > ---
> >  fs/iomap/buffered-io.c |  7 -------
> >  fs/xfs/xfs_aops.c      | 17 +++++++++++++++++
> >  fs/xfs/xfs_trans.c     |  3 +++
> >  fs/xfs/xfs_trans.h     | 25 +++++++++++++++++++++++++
> >  4 files changed, 45 insertions(+), 7 deletions(-)
> >
> > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> > index 10cc7979ce38..3c53fa6ce64d 100644
> > --- a/fs/iomap/buffered-io.c
> > +++ b/fs/iomap/buffered-io.c
> > @@ -1458,13 +1458,6 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
> >                       PF_MEMALLOC))
> >               goto redirty;
> >
> > -     /*
> > -      * Given that we do not allow direct reclaim to call us, we should
> > -      * never be called in a recursive filesystem reclaim context.
> > -      */
> > -     if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS))
> > -             goto redirty;
> > -
> >       /*
> >        * Is this page beyond the end of the file?
> >        *
> > diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> > index 2371187b7615..28db93d0da97 100644
> > --- a/fs/xfs/xfs_aops.c
> > +++ b/fs/xfs/xfs_aops.c
> > @@ -568,6 +568,16 @@ xfs_vm_writepage(
> >  {
> >       struct xfs_writepage_ctx wpc = { };
> >
> > +     /*
> > +      * Given that we do not allow direct reclaim to call us, we should
> > +      * never be called while in a filesystem transaction.
> > +      */
> > +     if (xfs_trans_context_active()) {
> > +             redirty_page_for_writepage(wbc, page);
> > +             unlock_page(page);
> > +             return 0;
> > +     }
>
> hmmm. Missing warning....
>
> > diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
> > index 44b11c64a15e..82c6735e40fc 100644
> > --- a/fs/xfs/xfs_trans.h
> > +++ b/fs/xfs/xfs_trans.h
> > @@ -268,16 +268,41 @@ xfs_trans_item_relog(
> >       return lip->li_ops->iop_relog(lip, tp);
> >  }
> >
> > +static inline bool
> > +xfs_trans_context_active(void)
> > +{
> > +     /* Use journal_info to indicate current is in a transaction */
> > +     if (WARN_ON_ONCE(current->journal_info != NULL))
> > +             return true;
> > +
> > +     return false;
> > +}
>
> Ah, this is wrong. The call sites should be:
>
>         if (WARN_ON_ONCE(xfs_trans_context_active())) {
>                 /* do error handling */
>                 return error_value;
>         }
>
> because we might want to use xfs_trans_context_active() to check if
> we are in a transaction context or not and that should not generate
> a warning. Also, placing the warning at the call site gives a more
> accurate indication of which IO path generated the warning....
>

Thanks for the explanation. I will update it in the next version.


-- 
Thanks
Yafang

      reply	other threads:[~2020-12-08  5:03 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-08  2:15 [PATCH v10 0/4] xfs: avoid transaction reservation recursion Yafang Shao
2020-12-08  2:15 ` [PATCH v10 1/4] mm: Add become_kswapd and restore_kswapd Yafang Shao
2020-12-08  2:15 ` [PATCH v10 2/4] xfs: use memalloc_nofs_{save,restore} in xfs transaction Yafang Shao
2020-12-08  2:46   ` Matthew Wilcox
2020-12-08  3:05     ` Yafang Shao
2020-12-08  2:15 ` [PATCH v10 3/4] xfs: refactor the usage around xfs_trans_context_{set,clear} Yafang Shao
2020-12-08  2:15 ` [PATCH v10 4/4] xfs: use current->journal_info to avoid transaction reservation recursion Yafang Shao
2020-12-08  2:41   ` Matthew Wilcox
2020-12-08  3:03     ` Yafang Shao
2020-12-08  4:20   ` Dave Chinner
2020-12-08  5:01     ` Yafang Shao [this message]

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='CALOAHbA8QtaxKx85U7UraU4D4MzjU=pR7rs0duVfPRvyarymSQ@mail.gmail.com' \
    --to=laoar.shao@gmail.com \
    --cc=akpm@linux-foundation.org \
    --cc=darrick.wong@oracle.com \
    --cc=david@fromorbit.com \
    --cc=dhowells@redhat.com \
    --cc=hch@infradead.org \
    --cc=hch@lst.de \
    --cc=jlayton@redhat.com \
    --cc=linux-cachefs@redhat.com \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=linux-xfs@vger.kernel.org \
    --cc=mhocko@kernel.org \
    --cc=willy@infradead.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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).