Re: [PATCH v2] netfs: fix writeback ENOMEM by using __GFP_NOFAIL for rolling buffer

[Zhou, Yun]

On 7/27/26 18:03, David Howells wrote:
> Yun Zhou <yun.zhou@xxxxxxxxxxxxx> wrote:
>
> > rolling_buffer_init() uses plain GFP_NOFS for its folio_queue allocation.
> > In the writeback path this can fail and trigger WARN_ON_ONCE(folio != NULL)
> > in netfs_writepages() when writeback_iter() returns additional dirty folios
> > left unhandled.
> >
> > Writeback must not fail with -ENOMEM. Fix this by adding a gfp_t parameter
> > to rolling_buffer_init() and passing GFP_NOFS | __GFP_NOFAIL from the
> > writeback path, ensuring the allocation always succeeds. Read paths
> > continue to use plain GFP_NOFS.
>
> I don't think this is the correct solution.  I think you're right that a gfp_t
> needs to be passed into rolling_buffer*(), but I think we need a mempool as
> well.
>
> I have most of the patch for that, but I think I need adjust things so that
> the read path uses GFP_KERNEL, not GFP_NOFS.

Got it. Your mempool approach looks good. Please let me know if you need 
anything from me.

BR,
Yun