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

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Date:	Wed, 30 Jun 2010 18:24:04 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Chris Wilson <chris@...is-wilson.co.uk>
Cc:	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>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.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?

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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