linux-kernel - Re: [RFC] mm: kmemleak: replace __GFP_NOFAIL to GFP_NOWAIT in gfp_kmemleak

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Message-ID: <20180424134148.qkvqqa4c37l6irvg@armageddon.cambridge.arm.com>
Date:   Tue, 24 Apr 2018 14:41:48 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Chunyu Hu <chuhu.ncepu@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Chunyu Hu <chuhu@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [RFC] mm: kmemleak: replace __GFP_NOFAIL to GFP_NOWAIT in
 gfp_kmemleak_mask

On Tue, Apr 24, 2018 at 07:20:57AM -0600, Michal Hocko wrote:
> On Mon 23-04-18 12:17:32, Chunyu Hu wrote:
> [...]
> > So if there is a new flag, it would be the 25th bits.
> 
> No new flags please. Can you simply store a simple bool into fail_page_alloc
> and have save/restore api for that?

For kmemleak, we probably first hit failslab. Something like below may
do the trick:

diff --git a/mm/failslab.c b/mm/failslab.c
index 1f2f248e3601..63f13da5cb47 100644
--- a/mm/failslab.c
+++ b/mm/failslab.c
@@ -29,6 +29,9 @@ bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags)
 	if (failslab.cache_filter && !(s->flags & SLAB_FAILSLAB))
 		return false;
 
+	if (s->flags & SLAB_NOLEAKTRACE)
+		return false;
+
 	return should_fail(&failslab.attr, s->object_size);
 }
 

Can we get a second should_fail() via should_fail_alloc_page() if a new
slab page is allocated?

-- 
Catalin