linux-kernel - Re: [PATCH] mm: Fix compile error when CONFIG

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Message-ID: <20250603140632.168190f9@gandalf.local.home>
Date: Tue, 3 Jun 2025 14:06:32 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Matthew Wilcox <willy@...radead.org>, Hugh Dickins <hughd@...gle.com>,
 LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org, Andrew Morton
 <akpm@...ux-foundation.org>, Christian Koenig <christian.koenig@....com>,
 Huang Rui <ray.huang@....com>, Matthew Auld <matthew.auld@...el.com>,
 Matthew Brost <matthew.brost@...el.com>, dri-devel@...ts.freedesktop.org,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
 <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie
 <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Subject: Re: [PATCH] mm: Fix compile error when CONFIG_SHMEM is not set

On Tue, 3 Jun 2025 10:54:49 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Tue, 3 Jun 2025 at 10:26, Steven Rostedt <rostedt@...dmis.org> wrote:
> >
> >  config DRM_TTM
> >         tristate
> > -       depends on DRM && MMU
> > +       depends on DRM && MMU && SHMEM  
> 
> Yeah, except I think you should just make it be
> 
>           depends on DRM && SHMEM
> 
> because SHMEM already depends on MMU.

Yeah, if I had made this a real patch I would have done that, but this was
only for seeing it it would work.

> 
> That said, our docs already say that if you disable SHMEM, it gets
> replaced by RAMFS, so maybe just having a ramfs version is the
> RightThing(tm).
> 
> I don't think such a ramfs version should just return 0 - much less an
> error. I think it should always redirty the page.
> 
> IOW, I think the "ramfs" version should look something like
> 
>         folio_mark_dirty(folio);
>         if (wbc->for_reclaim)
>                 return AOP_WRITEPAGE_ACTIVATE;  /* Return with folio locked */
>         folio_unlock(folio);
>         return 0;
> 
> which is what shmem does for the "page is locked" case.

I'll let someone that understand the code a bit more than I do to make such
a change. My patch was just a "this makes my system build" thing and let
those that know this code do the RightThing(tm).

-- Steve