[037/227] memcg: unify force charging conditions

Commit Message

Andrew Morton March 22, 2022, 9:40 p.m. UTC

From: Shakeel Butt <[e-mail]>
Subject: 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been replaced by __GFP_HIGH.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.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Shakeel Butt <[e-mail]>
Reviewed-by: Roman Gushchin <[e-mail]>
Cc: Roman Gushchin <[e-mail]>
Cc: Chris Down <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

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

Patch

--- a/mm/memcontrol.c~memcg-unify-force-charging-conditions
+++ a/mm/memcontrol.c
@@ -2566,15 +2566,6 @@  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_ATOMIC)
-		goto force;
-
-	/*
 	 * Prevent unbounded recursion when reclaim operations need to
 	 * allocate memory. This might exceed the limits temporarily,
 	 * but we prefer facilitating memory reclaim and getting back
@@ -2647,7 +2638,13 @@  retry:
 		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:
 	/*