linux-kernel - Re: [PATCH] mm, slub: do not add duplicate sysfs

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Message-ID: <alpine.DEB.2.11.1408271030360.17080@gentwo.org>
Date:	Wed, 27 Aug 2014 10:32:11 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	WANG Chao <chaowang@...hat.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	"open list:SLAB ALLOCATOR" <linux-mm@...ck.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm, slub: do not add duplicate sysfs

Maybe something like this may be a proper fix:

Subject: slub: Disable tracing of mergeable slabs

Tracing of mergeable slabs is confusing since the objects
of multiple slab caches will be traced. Moreover this creates
a situation where a mergeable slab will become unmergeable.

If tracing is desired then it may be best to switch merging
off for starters.

Signed-off-by: Christoph Lameter <cl@...ux.com>

Index: linux/mm/slub.c
===================================================================
--- linux.orig/mm/slub.c	2014-08-08 11:52:30.039681592 -0500
+++ linux/mm/slub.c	2014-08-27 10:30:16.508108726 -0500
@@ -4604,6 +4604,14 @@ static ssize_t trace_show(struct kmem_ca
 static ssize_t trace_store(struct kmem_cache *s, const char *buf,
 							size_t length)
 {
+	/*
+	 * Tracing a merged cache is going to give confusing results
+	 * as well as cause other issues like converting a mergeable
+	 * cache into an umergeable one.
+	 */
+	if (s->refcount > 1)
+		return -EINVAL;
+
 	s->flags &= ~SLAB_TRACE;
 	if (buf[0] == '1') {
 		s->flags &= ~__CMPXCHG_DOUBLE;
--
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