Re: [PATCH] mm: Fix compile error when CONFIG_SHMEM is not set

[Matthew Wilcox]

On Tue, Jun 03, 2025 at 10:29:59AM -0400, Steven Rostedt wrote:
> On Tue, 3 Jun 2025 01:02:36 -0700 (PDT)
> Hugh Dickins <hughd@xxxxxxxxxx> wrote:
> 
> > Agreed that ramfs does not use swap, so calling swap_writepage() would
> > be weird.  But, thanks for the build fix Steve, but it cannot be right
> > because return 0 says shmem_writeout() successfully sent the page to
> > swap, and that has unlocked the page (or soon will do so).  It should
> > return an error (-ENXIO?), but I haven't checked what the callers do with
> 
> Yeah, I figured it should return an error, but looking at the code I
> couldn't figure out what the proper error would be. Then I also noticed
> that the other stub functions just returned zero so I did the same.
> 
> Perhaps add a WARN_ON_ONCE() if it is called without CONFIG_SHMEM configured?

Or just make this module depend on SHMEM?  I don't think it makes much
sense to use it without being able to swap, and shmem can't swap ...