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

On 7/27/26 18:03, David Howells wrote:
> Yun Zhou <[email protected]> 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