[PATCH v2] drm/ttm: Fix compile error when CONFIG_SHMEM is not set

[Hugh Dickins]

On Wed, 4 Jun 2025, Thomas Hellström wrote:
> On Wed, 2025-06-04 at 08:51 -0400, Steven Rostedt wrote:
> > From: Steven Rostedt <rostedt at goodmis.org>
> > 
> > When CONFIG_SHMEM is not set, the following compiler error occurs:
> > 
> > ld: vmlinux.o: in function `ttm_backup_backup_page':
> > (.text+0x10363bc): undefined reference to `shmem_writeout'
> > make[3]: ***
> > [/work/build/trace/nobackup/linux.git/scripts/Makefile.vmlinux:91:
> > vmlinux.unstripped] Error 1
> > make[2]: *** [/work/build/trace/nobackup/linux.git/Makefile:1241:
> > vmlinux] Error 2
> > make[1]: *** [/work/build/trace/nobackup/linux.git/Makefile:248:
> > __sub-make] Error 2
> > make[1]: Leaving directory '/work/build/nobackup/tracetest'
> > make: *** [Makefile:248: __sub-make] Error 2
> > 
> > This is due to the replacement of writepage and calling
> > swap_writeout()
> > and shmem_writeout() directly. The issue is that when CONFIG_SHMEM is
> > not
> > defined, shmem_writeout() is also not defined.
> > 
> > The function ttm_backup_backup_page() called mapping->a_ops-
> > >writepage()
> > which was then changed to call shmem_writeout() directly.
> > 
> > Even before commit 84798514db50 ("mm: Remove swap_writepage() and
> > shmem_writepage()"), it didn't make sense to call anything other than
> > shmem_writeout() as the ttm_backup deals only with shmem folios.
> > 
> > Have DRM_TTM config option select SHMEM to guarantee that
> > shmem_writeout()
> > is available.
> > 
> > Link:
> > https://lore.kernel.org/all/20250602170500.48713a2b@gandalf.local.home/
> > 
> > Suggested-by: Hugh Dickins <hughd at google.com>
> > Fixes: 84798514db50 ("mm: Remove swap_writepage() and
> > shmem_writepage()")
> > Signed-off-by: Steven Rostedt (Google) <rostedt at goodmis.org>
> > ---
> > Changes since v1:
> > https://lore.kernel.org/all/20250602170500.48713a2b@gandalf.local.home/
> > 
> > - Instead of adding a shmem_writeout() stub, just make CONFIG_DRM_TTM
> >   select CONFIG_SHMEM (Hugh Dickins)
> > 
> >  drivers/gpu/drm/Kconfig | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> > index f094797f3b2b..ded28c71d89c 100644
> > --- a/drivers/gpu/drm/Kconfig
> > +++ b/drivers/gpu/drm/Kconfig
> > @@ -188,6 +188,7 @@ source "drivers/gpu/drm/display/Kconfig"
> >  config DRM_TTM
> >  	tristate
> >  	depends on DRM && MMU
> > +	select SHMEM
> >  	help
> >  	  GPU memory management subsystem for devices with multiple
> >  	  GPU memory types. Will be enabled automatically if a
> > device driver
> 
> Reviewed-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>

Acked-by: Hugh Dickins <hughd at google.com>

Thanks a lot!