From: Dave Chinner <dgc@kernel.org>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: Morduan Zang <zhangdandan@uniontech.com>,
cem@kernel.org, zhanjun@uniontech.com, hch@lst.de,
dchinner@redhat.com, stable@vger.kernel.org,
linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org,
syzbot+d78ace33ad4ee69329d5@syzkaller.appspotmail.com
Subject: Re: [PATCH] xfs: use GFP_NOFS in __xfs_trans_alloc
Date: Fri, 13 Mar 2026 07:28:11 +1100 [thread overview]
Message-ID: <abMh2395Dkbrdgy0@dread> (raw)
In-Reply-To: <20260312142601.GI1770774@frogsfrogsfrogs>
On Thu, Mar 12, 2026 at 07:26:01AM -0700, Darrick J. Wong wrote:
> On Thu, Mar 12, 2026 at 03:22:14PM +0800, Morduan Zang wrote:
> > __xfs_trans_alloc() allocates the transaction structure before
> > xfs_trans_set_context() establishes the nofs context. If memory reclaim
> > enters XFS through xfs_vn_sync_lazytime(), this GFP_KERNEL allocation can
> > trigger a warning from the reclaim path.
> >
> > Use GFP_NOFS for the transaction allocation to avoid filesystem reclaim
> > recursion before the nofs context is set.
>
> Why doesn't filesystem reclaim itself set PF_MEMALLOC_NOFS for us?
Because kswapd based memory reclaim runs in GFP_KERNEL
memory allocation context. i.e. we're not in a recursion path here
potentially holding other filesystem resources that we could
deadlock on.
i.e. GFP_NOFS allocations are used to stop -direct reclaim- from
recursing back into filesystem reclaim - it does not (and should
not) stop kswapd from being able to reclaim filesystem objects.
-Dave.
--
Dave Chinner
dgc@kernel.org
next prev parent reply other threads:[~2026-03-12 20:28 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-12 7:22 [PATCH] xfs: use GFP_NOFS in __xfs_trans_alloc Morduan Zang
2026-03-12 14:26 ` Darrick J. Wong
2026-03-12 20:28 ` Dave Chinner [this message]
2026-03-12 20:25 ` Dave Chinner
2026-03-16 9:18 ` Christoph Hellwig
2026-03-18 21:01 ` Dave Chinner
2026-03-20 10:03 ` [PATCH] xfs: defer lazytime timestamp updates to inodegc during eviction Morduan Zang
2026-03-24 15:14 ` Jan Kara
2026-03-25 6:38 ` Christoph Hellwig
2026-03-25 11:34 ` Jan Kara
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