From: Miles Chen <miles.chen@mediatek.com>
To: Christopher Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Andrew Morton <akpm@linux-foundation.org>,
<linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
<wsd_upstream@mediatek.com>, <linux-mediatek@lists.infradead.org>
Subject: Re: [PATCH] slub: Fix sysfs duplicate filename creation when slub_debug=O
Date: Thu, 9 Nov 2017 16:52:34 +0800 [thread overview]
Message-ID: <1510217554.32371.17.camel@mtkswgap22> (raw)
In-Reply-To: <alpine.DEB.2.20.1711080903460.6161@nuc-kabylake>
On Wed, 2017-11-08 at 09:05 -0600, Christopher Lameter wrote:
> On Wed, 8 Nov 2017, Miles Chen wrote:
>
> > > Ok then the aliasing failed for some reason. The creation of the unique id
> > > and the alias detection needs to be in sync otherwise duplicate filenames
> > > are created. What is the difference there?
> >
> > The aliasing failed because find_mergeable() returns if (flags &
> > SLAB_NEVER_MERGE) is true. So we do not go to search for alias caches.
> >
> > __kmem_cache_alias()
> > find_mergeable()
> > kmem_cache_flags() --> setup flag by the slub_debug
> > if (flags & SLAB_NEVER_MERGE) return NULL;
> > ...
> > search alias logic...
> >
> >
> > The flags maybe changed if disable_higher_order_debug=1. So the
> > unmergeable cache becomes mergeable later.
>
> Ok so make sure taht the aliasing logic also clears those flags before
> checking for SLAB_NEVER_MERGE.
>
> > > The clearing of the DEBUG_METADATA_FLAGS looks ok to me. kmem_cache_alias
> > > should do the same right?
> > >
> > Yes, I think clearing DEBUG_METADATA flags in kmem_cache_alias is
> > another solution for this issue.
> >
> > We will need to do calculate_sizes() by using original flags and compare
> > the order of s->size and s->object_size when
> > disable_higher_order_debug=1.
>
> Hmmm... Or move the aliasing check to a point where we know the size of
> the slab objects?
The biggest concern is that we may have some merged caches even if we
enable CONFIG_SLUB_DEBUG_ON and slub_debug=O. So a developer cannot say
"I set CONFIG_SLUB_DEBUG_ON=y to stop all slab merging".
(https://www.spinics.net/lists/linux-mm/msg77919.html)
In this fix patch, it disables slab merging if SLUB_DEBUG=O and
CONFIG_SLUB_DEBUG_ON=y but the debug features are disabled by the
disable_higher_order_debug logic and it holds the "slab merging is off
if any debug features are enabled" behavior.
next prev parent reply other threads:[~2017-11-09 8:52 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-07 3:05 [PATCH] slub: Fix sysfs duplicate filename creation when slub_debug=O miles.chen
2017-11-07 15:22 ` Christopher Lameter
2017-11-08 5:32 ` Miles Chen
2017-11-08 15:05 ` Christopher Lameter
2017-11-09 8:52 ` Miles Chen [this message]
2017-11-09 15:49 ` Christopher Lameter
2017-11-09 23:51 ` Miles Chen
2017-11-10 16:02 ` Christopher Lameter
2017-11-12 1:40 ` Miles Chen
2017-11-08 3:05 ` kbuild test robot
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