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

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Message-Id: <20220210081437.1884008-3-shakeelb@google.com>
Date:   Thu, 10 Feb 2022 00:14:35 -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 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 let 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__GFP_ATOMIC has been replaced by __GFP_HIGH.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 reclaim 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 kernel which also have __GFP_ACCOUNT (or SLAB_ACCOUNT) and
does not allow reclaim for now. The reason for this patch is to simplify
the reasoning of the following patches.

Signed-off-by: Shakeel Butt <shakeelb@...gle.com>
---
 mm/memcontrol.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c40c27822802..ae73a40818b0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2560,15 +2560,6 @@ 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,
@@ -2642,7 +2633,13 @@ 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