linux-kernel - Re: [PATCH] slub: try to get cpu partial slab even if we get enough objects for cpu freelist

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Message-ID: <CAAmzW4M9WMnxVKpR00SqufHadY-=i0Jgf8Ktydrw5YXK8VwJ7A@mail.gmail.com>
Date:	Thu, 16 Aug 2012 01:35:41 +0900
From:	JoonSoo Kim <js1304@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Pekka Enberg <penberg@...nel.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH] slub: try to get cpu partial slab even if we get enough
 objects for cpu freelist

2012/8/16 Christoph Lameter <cl@...ux.com>:
> On Thu, 16 Aug 2012, Joonsoo Kim wrote:
>
>> s->cpu_partial determine the maximum number of objects kept
>> in the per cpu partial lists of a processor. Currently, it is used for
>> not only per cpu partial list but also cpu freelist. Therefore
>> get_partial_node() doesn't work properly according to our first intention.
>
> The "cpu freelist" in slub is the number of free objects in a specific
> page. There is nothing that s->cpu_partial can do about that.
>
> Maybe I do not understand you correctly. Could you explain this in some
> more detail?

I assume that cpu slab and cpu partial slab are not same thing.

In my definition,
cpu slab is in c->page,
cpu partial slab is in c->partial

When we have no free objects in cpu slab and cpu partial slab, we try
to get slab via get_partial_node().
In that function, we call acquire_slab(). Then we hit "!object" case
(for cpu slab).
In that case, we test available with s->cpu_partial.

I think that s->cpu_partial is for cpu partial slab, not cpu slab.
So this test is not proper.
This patch is for correcting this.

Thanks!
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