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Patch "slub: clean up code for kmem cgroup support to kmem_cache_free_bulk" has been added to the 4.5-stable tree

PATCH [email protected] 1 participant 1 message May 2, 2016

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This is a note to let you know that I've just added the patch titled

slub: clean up code for kmem cgroup support to kmem_cache_free_bulk

to the 4.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
slub-clean-up-code-for-kmem-cgroup-support-to-kmem_cache_free_bulk.patch
and it can be found in the queue-4.5 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From 376bf125ac781d32e202760ed7deb1ae4ed35d31 Mon Sep 17 00:00:00 2001

From: Jesper Dangaard Brouer <[email protected]>
Date: Tue, 15 Mar 2016 14:53:32 -0700
Subject: slub: clean up code for kmem cgroup support to kmem_cache_free_bulk

From: Jesper Dangaard Brouer <[email protected]>

commit 376bf125ac781d32e202760ed7deb1ae4ed35d31 upstream.

This change is primarily an attempt to make it easier to realize the optimizations the compiler performs in-case CONFIG_MEMCG_KMEM is not enabled.

Performance wise, even when CONFIG_MEMCG_KMEM is compiled in, the overhead is zero. This is because, as long as no process have enabled kmem cgroups accounting, the assignment is replaced by asm-NOP operations. This is possible because memcg_kmem_enabled() uses a static_key_false() construct.

It also helps readability as it avoid accessing the p[] array like:
p[size - 1] which "expose" that the array is processed backwards inside helper function build_detached_freelist().

Lastly this also makes the code more robust, in error case like passing NULL pointers in the array. Which were previously handled before commit 033745189b1b ("slub: add missing kmem cgroup support to kmem_cache_free_bulk").

Fixes 033745189b1b ("slub: add missing kmem cgroup support to kmem_cache_free_bulk")
Signed-off-by Jesper Dangaard Brouer <[email protected]>
Cc Christoph Lameter <[email protected]>
Cc Pekka Enberg <[email protected]>
Cc David Rientjes <[email protected]>
Cc Joonsoo Kim <[email protected]>
Cc Vladimir Davydov <[email protected]>
Signed-off-by Andrew Morton <[email protected]>
Signed-off-by Linus Torvalds <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 mm/slub.c |   22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)
mm/slub.c +11 -11
@@ -2815,6 +2815,7 @@ struct detached_freelist {
 	void *tail;
 	void *freelist;
 	int cnt;
+	struct kmem_cache *s;
 };
 
 /*

@@ -2829,8 +2830,9 @@ struct detached_freelist {
  * synchronization primitive.  Look ahead in the array is limited due
  * to performance reasons.
  */
-static int build_detached_freelist(struct kmem_cache *s, size_t size,
-				   void **p, struct detached_freelist *df)
+static inline
+int build_detached_freelist(struct kmem_cache *s, size_t size,
+			    void **p, struct detached_freelist *df)
 {
 	size_t first_skipped_index = 0;
 	int lookahead = 3;

@@ -2846,8 +2848,11 @@ static int build_detached_freelist(struc
 	if (!object)
 		return 0;
 
+	/* Support for memcg, compiler can optimize this out */
+	df->s = cache_from_obj(s, object);
+
 	/* Start new detached freelist */
-	set_freepointer(s, object, NULL);
+	set_freepointer(df->s, object, NULL);
 	df->page = virt_to_head_page(object);
 	df->tail = object;
 	df->freelist = object;

@@ -2862,7 +2867,7 @@ static int build_detached_freelist(struc
 		/* df->page is always set at this point */
 		if (df->page == virt_to_head_page(object)) {
 			/* Opportunity build freelist */
-			set_freepointer(s, object, df->freelist);
+			set_freepointer(df->s, object, df->freelist);
 			df->freelist = object;
 			df->cnt++;
 			p[size] = NULL; /* mark object processed */

@@ -2881,25 +2886,20 @@ static int build_detached_freelist(struc
 	return first_skipped_index;
 }
 
-
 /* Note that interrupts must be enabled when calling this function. */
-void kmem_cache_free_bulk(struct kmem_cache *orig_s, size_t size, void **p)
+void kmem_cache_free_bulk(struct kmem_cache *s, size_t size, void **p)
 {
 	if (WARN_ON(!size))
 		return;
 
 	do {
 		struct detached_freelist df;
-		struct kmem_cache *s;
-
-		/* Support for memcg */
-		s = cache_from_obj(orig_s, p[size - 1]);
 
 		size = build_detached_freelist(s, size, p, &df);
 		if (unlikely(!df.page))
 			continue;
 
-		slab_free(s, df.page, df.freelist, df.tail, df.cnt, _RET_IP_);
+		slab_free(df.s, df.page, df.freelist, df.tail, df.cnt,_RET_IP_);
 	} while (likely(size));
 }
 EXPORT_SYMBOL(kmem_cache_free_bulk);

Patches currently in stable-queue which might be from [email protected] are

queue-4.5/slub-clean-up-code-for-kmem-cgroup-support-to-kmem_cache_free_bulk.patch