Re: [PATCH] xfs: use GFP_NOFS in __xfs_trans_alloc

[Dave Chinner]

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@xxxxxxxxxx