linux-kernel - [PATCH v2 2/4] memcg: unify force charging conditions

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Date:   Thu, 10 Feb 2022 22:49:15 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...e.com>, Roman Gushchin <guro@...com>
Cc:     Chris Down <chris@...isdown.name>,
        Andrew Morton <akpm@...ux-foundation.org>,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Shakeel Butt <shakeelb@...gle.com>
Subject: [PATCH v2 2/4] memcg: unify force charging conditions

Currently the kernel force charges the allocations which have __GFP_HIGH
flag without triggering the memory reclaim. __GFP_HIGH indicates that
the caller is high priority and since commit 869712fd3de5 ("mm:
memcontrol: fix network errors from failing __GFP_ATOMIC charges") the
kernel lets such allocations do force charging. Please note that
__GFP_ATOMIC has been replaced by __GFP_HIGH.

__GFP_HIGH does not tell if the caller can block or can trigger reclaim.
There are separate checks to determine that. So, there is no need to
skip reclaiming for __GFP_HIGH allocations. So, handle __GFP_HIGH
together with __GFP_NOFAIL which also does force charging.

Please note that this is a noop change as there are no __GFP_HIGH
allocators in the kernel which also have __GFP_ACCOUNT (or SLAB_ACCOUNT)
and does not allow reclaim for now.

Signed-off-by: Shakeel Butt <shakeelb@...gle.com>
Reviewed-by: Roman Gushchin <guro@...com>
---
Changes since v1:
- None

 mm/memcontrol.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f12e489ba9b8..292b0b99a2c7 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2564,15 +2564,6 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
 		goto retry;
 	}

-	/*
-	 * Memcg doesn't have a dedicated reserve for atomic
-	 * allocations. But like the global atomic pool, we need to
-	 * put the burden of reclaim on regular allocation requests
-	 * and let these go through as privileged allocations.
-	 */
-	if (gfp_mask & __GFP_HIGH)
-		goto force;
-
 	/*
 	 * Prevent unbounded recursion when reclaim operations need to
 	 * allocate memory. This might exceed the limits temporarily,
@@ -2646,7 +2637,13 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
 		goto retry;
 	}
 nomem:
-	if (!(gfp_mask & __GFP_NOFAIL))
+	/*
+	 * Memcg doesn't have a dedicated reserve for atomic
+	 * allocations. But like the global atomic pool, we need to
+	 * put the burden of reclaim on regular allocation requests
+	 * and let these go through as privileged allocations.
+	 */
+	if (!(gfp_mask & (__GFP_NOFAIL | __GFP_HIGH)))
 		return -ENOMEM;
 force:
 	/*
-- 
2.35.1.265.g69c8d7142f-goog