Re: iomap_writepages WARN_ON_ONCE(PF_MEMALLOC)

Matthew Wilcox <[email protected]> Sat, 4 Jul 2026 01:56:58 +0100

Newsgroups	dev.linux.lists.gfs2,org.kernel.vger.cgroups,org.kernel.vger.linux-fsdevel,org.kernel.vger.linux-kernel,org.kernel.vger.linux-xfs,org.kvack.linux-mm
Message-ID	<[email protected]>

On Thu, Jul 02, 2026 at 03:59:24AM -0700, Christoph Hellwig wrote:
> On Wed, Jul 01, 2026 at 10:51:06PM +0200, Andreas Gruenbacher wrote:
> > Do you have any suggestions?
> > 
> > The above is on RHEL-8, but a similar code path exists in cgroups v2,
> > triggered via:
> > 
> >   echo reclaim_amount > /sys/fs/cgroup/.../memory.reclaim
> > 
> > That code path starts with:
> > 
> > memory_reclaim -> user_proactive_reclaim -> try_to_free_mem_cgroup_pages ->
> 
> PF_MEMALLOC is a sign of direct reclaim.  cgroup code is doing really
> weird things when it is set and it is doing writeback.

If we're going to blame the cgroup people for doing weird things, let's
cc them so they stand a chance of seeing this ... original at:

https://lore.kernel.org/linux-fsdevel/CAHc6FU4tz8-HmEf2_XKT0NT8N=rv5OMcY79PxTACkXAVLOAUpg@mail.gmail.com/