linux-kernel - Re: [Intel-gfx] [PATCH] drm/i915: Selectively enable self-reclaim

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Date:	Thu,  1 Jul 2010 10:55:29 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	kosaki.motohiro@...fujitsu.com,
	Chris Wilson <chris@...is-wilson.co.uk>,
	Dave Airlie <airlied@...il.com>, earny@...4u.de,
	Roman Jarosz <kedgedev@...il.com>,
	intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	jcnengel@...glemail.com,
	"A. Boulan" <arnaud.boulan@...ertysurf.fr>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Pekka Enberg <penberg@...helsinki.fi>,
	A Rojas <nqn1976list@...il.com>, rientjes@...gle.com,
	michael@...nelt.co.at, stable@...nel.org,
	Vefa Bicakci <bicave@...eronline.com>
Subject: Re: [Intel-gfx] [PATCH] drm/i915: Selectively enable self-reclaim

> On Wed, Jun 30, 2010 at 4:07 PM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > That commit changes the page cache allocation to use
> >
> > +                                          mapping_gfp_mask (mapping) |
> > +                                          __GFP_COLD |
> > +                                          gfpmask);
> >
> > if I read it right. And the default mapping_gfp_mask() is
> > GFP_HIGHUSER_MOVABLE, so I think you get all of
> > (__GFP_WAIT | __GFP_IO | __GFP_FS | __GFP_HARDWALL | __GFP_HIGHMEM)
> > set by default.
> 
> .. and then I left out the one flag I _meant_ to have there, namely
> __GFP_MOVABLE.
> 
> > The old code didn't just play games with ~__GFP_NORETRY and change
> > that at runtime (which was buggy - no locking, no protection, no
> > nothing), it also initialized the gfp mask. And that code also got
> > removed:
> 
> In fact, I don't really see why we should use that mapping_gfp_mask()
> at all, since all allocations should be going through that
> i915_gem_object_get_pages() function anyway. So why not just change
> that function to ignore the default gfp mask for the mapping, and just
> use the mask that the o915 driver wants?
> 
> Btw, why did it want to mark the pages reclaimable?

I'm not GEM expert at all. but as far as I read following documentation,

http://lwn.net/Articles/283798/

GEM memory have pin and unpin state and unpined memory can be reclaimed.
but it's just guess. So, I wonder if your patch solve the issue. I don't imazine a memory 
state which "swap-out is safe, but compaction is unsafe".

Dave, if you have good documentation which we understand GEM memory management,
could you send us?

   - kosaki

> 
> Anyway, what I'm suggesting somebody who sees this test is just
> something like the patch below (whitespace-damage - I'm cutting and
> pasting, it's a trivial one-liner).  Does this change any behavior?
> Vefa?
> 
>                     Linus
> 
> ---
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 9ded3da..ec8ed6b 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2239,7 +2239,7 @@ i915_gem_object_get_pages(struct drm_gem_object *obj,
>         mapping = inode->i_mapping;
>         for (i = 0; i < page_count; i++) {
>                 page = read_cache_page_gfp(mapping, i,
> -                                          mapping_gfp_mask (mapping) |
> +                                          GFP_HIGHMEM |
>                                            __GFP_COLD |
>                                            gfpmask);
>                 if (IS_ERR(page))
> --
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