linux-kernel - [PATCH v2] mm/failslab: By default, do not fail allocations with direct reclaim only

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Message-Id: <20190520214514.81360-1-drinkcat@chromium.org>
Date:   Tue, 21 May 2019 05:45:14 +0800
From:   Nicolas Boichat <drinkcat@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     David Rientjes <rientjes@...gle.com>,
        Nicolas Boichat <drinkcat@...omium.org>,
        Michal Hocko <mhocko@...e.com>, Joe Perches <joe@...ches.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-mm@...ck.org, Akinobu Mita <akinobu.mita@...il.com>,
        Pekka Enberg <penberg@...nel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] mm/failslab: By default, do not fail allocations with direct reclaim only

When failslab was originally written, the intention of the
"ignore-gfp-wait" flag default value ("N") was to fail
GFP_ATOMIC allocations. Those were defined as (__GFP_HIGH),
and the code would test for __GFP_WAIT (0x10u).

However, since then, __GFP_WAIT was replaced by __GFP_RECLAIM
(___GFP_DIRECT_RECLAIM|___GFP_KSWAPD_RECLAIM), and GFP_ATOMIC is
now defined as (__GFP_HIGH|__GFP_ATOMIC|__GFP_KSWAPD_RECLAIM).

This means that when the flag is false, almost no allocation
ever fails (as even GFP_ATOMIC allocations contain
___GFP_KSWAPD_RECLAIM).

Restore the original intent of the code, by ignoring calls
that directly reclaim only (__GFP_DIRECT_RECLAIM), and thus,
failing GFP_ATOMIC calls again by default.

Fixes: 71baba4b92dc1fa1 ("mm, page_alloc: rename __GFP_WAIT to __GFP_RECLAIM")
Signed-off-by: Nicolas Boichat <drinkcat@...omium.org>
Reviewed-by: Akinobu Mita <akinobu.mita@...il.com>
Acked-by: David Rientjes <rientjes@...gle.com>
---
 mm/failslab.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/failslab.c b/mm/failslab.c
index ec5aad211c5be97..f92fed91ac2360a 100644
--- a/mm/failslab.c
+++ b/mm/failslab.c
@@ -23,7 +23,8 @@ bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags)
 	if (gfpflags & __GFP_NOFAIL)
 		return false;

-	if (failslab.ignore_gfp_reclaim && (gfpflags & __GFP_RECLAIM))
+	if (failslab.ignore_gfp_reclaim &&
+			(gfpflags & __GFP_DIRECT_RECLAIM))
 		return false;

 	if (failslab.cache_filter && !(s->flags & SLAB_FAILSLAB))
-- 
2.21.0.1020.gf2820cf01a-goog