Re: [PATCH v2] mm: Fix error handling in __filemap_get_folio() with FGP_NOWAIT

Matthew Wilcox
2025-02-24T15:33:32Z

On Mon, Feb 24, 2025 at 03:17:44PM +0100, Christoph Hellwig wrote:
> On Mon, Feb 24, 2025 at 05:13:28AM -0300, Raphael S. Carvalho wrote:
> > + if (err) {
> > + /* Prevents -ENOMEM from escaping to user space with FGP_NOWAIT */
> > + if ((fgp_flags & FGP_NOWAIT) && err == -ENOMEM)
> > + err = -EAGAIN;
> > return ERR_PTR(err);
>
> I don't think the comment is all that useful. It's also overly long.
>
> I'd suggest this instead:
>
> /*
> * When NOWAIT I/O fails to allocate folios this could
> * be due to a nonblocking memory allocation and not
> * because the system actually is out of memory.
> * Return -EAGAIN so that there caller retries in a
> * blocking fashion instead of propagating -ENOMEM
> * to the application.
> */

I don't think it needs a comment at all, but the memory allocation
might be for something other than folios, so your suggested comment
is misleading.