Re: [PATCH] netfs: fix ENOMEM handling in netfs_writepages() to drain all dirty folios

[Zhou, Yun]

On 7/23/26 12:59, Christoph Hellwig wrote:
> On Tue, Jul 07, 2026 at 01:25:55PM +0800, Yun Zhou wrote:
> > When netfs_create_write_req() fails with -ENOMEM in netfs_writepages(),
> > the couldnt_start error path redirties and unlocks the first folio,
>
> writeback must use mempools to back resoures, or __GFP_NOFAIL if it
> can't for some reason.  -ENOMEM must not happend in writeback paths
> or your toast.  So please fix the cause of this error and not the
> symptoms.

Thanks for the review. You're right - writeback should not fail with ENOMEM.

I'll follow your suggestion and use __GFP_NOFAIL for the allocation in 
the writeback path. The ENOMEM here comes from rolling_buffer_init() 
which uses plain GFP_NOFS for its folio_queue allocation.

Using mempools would be the more robust approach, but it requires adding 
a new mempool, modifying the rolling_buffer_init() signature and all its 
callers, plus the init/destroy lifecycle - a much larger change. 
__GFP_NOFAIL is a minimal fix that achieves the same goal for the 
writeback path.

Will send v2 shortly.