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From: Christoph Lameter <cl@linux.com>
To: Dave Hansen <dave@sr71.net>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	kirill.shutemov@linux.intel.com, Andi Kleen <ak@linux.intel.com>
Subject: Re: [RFC][PATCH 2/3] mm: slab: move around slab ->freelist for cmpxchg
Date: Thu, 12 Dec 2013 17:46:02 +0000	[thread overview]
Message-ID: <00000142e7ea519d-8906d225-c99c-44b5-b381-b573c75fd097-000000@email.amazonses.com> (raw)
In-Reply-To: <20131211224025.70B40B9C@viggo.jf.intel.com>

On Wed, 11 Dec 2013, Dave Hansen wrote:

>
> The write-argument to cmpxchg_double() must be 16-byte aligned.
> We used to align 'struct page' itself in order to guarantee this,
> but that wastes 8-bytes per page.  Instead, we take 8-bytes
> internal to the page before page->counters and move freelist
> between there and the existing 8-bytes after counters.  That way,
> no matter how 'stuct page' itself is aligned, we can ensure that
> we have a 16-byte area with which to to this cmpxchg.

Well this adds additional branching to the fast paths.

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Lameter <cl@linux.com>
To: Dave Hansen <dave@sr71.net>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	kirill.shutemov@linux.intel.com, Andi Kleen <ak@linux.intel.com>
Subject: Re: [RFC][PATCH 2/3] mm: slab: move around slab ->freelist for cmpxchg
Date: Thu, 12 Dec 2013 17:46:02 +0000	[thread overview]
Message-ID: <00000142e7ea519d-8906d225-c99c-44b5-b381-b573c75fd097-000000@email.amazonses.com> (raw)
In-Reply-To: <20131211224025.70B40B9C@viggo.jf.intel.com>

On Wed, 11 Dec 2013, Dave Hansen wrote:

>
> The write-argument to cmpxchg_double() must be 16-byte aligned.
> We used to align 'struct page' itself in order to guarantee this,
> but that wastes 8-bytes per page.  Instead, we take 8-bytes
> internal to the page before page->counters and move freelist
> between there and the existing 8-bytes after counters.  That way,
> no matter how 'stuct page' itself is aligned, we can ensure that
> we have a 16-byte area with which to to this cmpxchg.

Well this adds additional branching to the fast paths.

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  reply	other threads:[~2013-12-12 17:46 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-12-11 22:40 [RFC][PATCH 0/3] re-shrink 'struct page' when SLUB is on Dave Hansen
2013-12-11 22:40 ` Dave Hansen
2013-12-11 22:40 ` [RFC][PATCH 1/3] mm: slab: create helpers for slab ->freelist pointer Dave Hansen
2013-12-11 22:40   ` Dave Hansen
2013-12-12 19:32   ` Christoph Lameter
2013-12-12 19:32     ` Christoph Lameter
2013-12-11 22:40 ` [RFC][PATCH 2/3] mm: slab: move around slab ->freelist for cmpxchg Dave Hansen
2013-12-11 22:40   ` Dave Hansen
2013-12-12 17:46   ` Christoph Lameter [this message]
2013-12-12 17:46     ` Christoph Lameter
2013-12-12 19:39     ` Dave Hansen
2013-12-12 19:39       ` Dave Hansen
2013-12-12 23:40     ` Andi Kleen
2013-12-12 23:40       ` Andi Kleen
2013-12-11 22:40 ` [RFC][PATCH 3/3] mm: slabs: reset page at free Dave Hansen
2013-12-11 22:40   ` Dave Hansen
2013-12-12 17:44   ` Christoph Lameter
2013-12-12 17:44     ` Christoph Lameter

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