Re: [PATCH] mm,page_alloc: apply gfp_allowed_mask before the first allocation attempt.

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

Michal Hocko wrote:
> On Fri 01-09-17 23:11:31, Tetsuo Handa wrote:
> > We are by error initializing alloc_flags before gfp_allowed_mask is
> > applied. Apply gfp_allowed_mask before initializing alloc_flags so that
> > the first allocation attempt uses correct flags.
> 
> It would be worth noting that this will not matter in most cases,
> actually when only the node reclaim is enabled we can misbehave because
> NOFS request for PM paths would be ignored.
> 
> > Fixes: 9cd7555875bb09da ("mm, page_alloc: split alloc_pages_nodemask()")
> 
> AFAICS this patch hasn't changed the logic and it was broken since
> 83d4ca8148fd ("mm, page_alloc: move __GFP_HARDWALL modifications out of
> the fastpath")

Indeed. Updated patch follows.

> 
> > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > Cc: Mel Gorman <mgorman@techsingularity.net>
> > Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
> > Cc: Vlastimil Babka <vbabka@suse.cz>
> > Cc: Jesper Dangaard Brouer <brouer@redhat.com>
> 
> Other than that this looks correct to me. 
> Acked-by: Michal Hocko <mhocko@suse.com>
> 
> I wish we can finally get rid of gfp_allowed_mask. I have it on my todo
> list but never got to it.
> 
> Thanks!
> 
----------
>From b454863bea884158a25460aa29a26c5feb16fe94 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Fri, 1 Sep 2017 23:11:31 +0900
Subject: [PATCH v2] mm,page_alloc: apply gfp_allowed_mask before the first
 allocation attempt.

We are by error initializing alloc_flags before gfp_allowed_mask is
applied. This could cause problems after pm_restrict_gfp_mask() is
called during suspend operation. Apply gfp_allowed_mask before
initializing alloc_flags so that the first allocation attempt uses
correct flags.

Fixes: 83d4ca8148fd9092 ("mm, page_alloc: move __GFP_HARDWALL modifications out of the fastpath")
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
---
 mm/page_alloc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6dbc49e..a123dee 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4179,10 +4179,11 @@ struct page *
 {
 	struct page *page;
 	unsigned int alloc_flags = ALLOC_WMARK_LOW;
-	gfp_t alloc_mask = gfp_mask; /* The gfp_t that was actually used for allocation */
+	gfp_t alloc_mask; /* The gfp_t that was actually used for allocation */
 	struct alloc_context ac = { };
 
 	gfp_mask &= gfp_allowed_mask;
+	alloc_mask = gfp_mask;
 	if (!prepare_alloc_pages(gfp_mask, order, preferred_nid, nodemask, &ac, &alloc_mask, &alloc_flags))
 		return NULL;
 
-- 
1.8.3.1

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