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From: Andrew Morton <akpm@linux-foundation.org>
To: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Christoph Lameter <cl@linux.com>,
	David Rientjes <rientjes@google.com>,
	Eric Dumazet <eric.dumazet@gmail.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	linux-kernel@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	kamezawa.hiroyu@jp.fujitsu.com, kosaki.motohiro@jp.fujitsu.com,
	Joe Perches <joe@perches.com>
Subject: Re: [slubllv7 05/17] mm: Rearrange struct page
Date: Thu, 9 Jun 2011 09:45:26 -0700
Message-ID: <20110609094526.1571774c.akpm@linux-foundation.org> (raw)
In-Reply-To: <4DF0991E.6060907@cs.helsinki.fi>

On Thu, 09 Jun 2011 12:57:50 +0300 Pekka Enberg <penberg@cs.helsinki.fi> wrote:

> On 6/1/11 8:25 PM, Christoph Lameter wrote:
> > We need to be able to use cmpxchg_double on the freelist and object count
> > field in struct page. Rearrange the fields in struct page according to
> > doubleword entities so that the freelist pointer comes before the counters.
> > Do the rearranging with a future in mind where we use more doubleword
> > atomics to avoid locking of updates to flags/mapping or lru pointers.
> >
> > Create another union to allow access to counters in struct page as a
> > single unsigned long value.
> >
> > The doublewords must be properly aligned for cmpxchg_double to work.
> > Sadly this increases the size of page struct by one word on some architectures.
> > But as a resultpage structs are now cacheline aligned on x86_64.

Is it worth this cost?

> > Signed-off-by: Christoph Lameter<cl@linux.com>
> 
> I'd like to queue this SLUB patch series to linux-next through slab.git. 
> Any NAKs or ACKs for this patch?
> 
> >   include/linux/mm_types.h |   89 +++++++++++++++++++++++++++++++----------------
> >   1 file changed, 60 insertions(+), 29 deletions(-)
> >
> > Index: linux-2.6/include/linux/mm_types.h
> > ===================================================================
> > --- linux-2.6.orig/include/linux/mm_types.h	2011-05-31 09:46:41.912987862 -0500
> > +++ linux-2.6/include/linux/mm_types.h	2011-05-31 09:46:44.282987846 -0500
> > @@ -30,52 +30,74 @@ struct address_space;
> >    * moment. Note that we have no way to track which tasks are using
> >    * a page, though if it is a pagecache page, rmap structures can tell us
> >    * who is mapping it.
> > + *
> > + * The objects in struct page are organized in double word blocks in
> > + * order to allows us to use atomic double word operations on portions
> > + * of struct page. That is currently only used by slub but the arrangement
> > + * allows the use of atomic double word operations on the flags/mapping
> > + * and lru list pointers also.

I don't really like the word "word" much.  There's always uncertainty
about whether thee and me are talking about the same thing.  And
perhaps one day words will be 64-bit.

So if we mean 32-bit, let's say 32-bit?

> > +/*
> > + * If another subsystem starts using the double word pairing for atomic
> > + * operations on struct page then it must change the #if to ensure
> > + * proper alignment of the page struct.
> > + */
> > +#if defined(CONFIG_SLUB)&&  defined(CONFIG_CMPXCHG_LOCAL)
> > +	__attribute__((__aligned__(2*sizeof(unsigned long))))
> > +#endif

I guess we need a "hey, use __aligned" checkpatch rule.

  reply index

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-06-01 17:25 [slubllv7 00/17] SLUB: Lockless freelists for objects V7 Christoph Lameter
2011-06-01 17:25 ` [slubllv7 01/17] slub: Push irq disable into allocate_slab() Christoph Lameter
2011-06-01 17:25 ` [slubllv7 02/17] slub: Do not use frozen page flag but a bit in the page counters Christoph Lameter
2011-06-01 17:25 ` [slubllv7 03/17] slub: Move page->frozen handling near where the page->freelist handling occurs Christoph Lameter
2011-06-01 17:25 ` [slubllv7 04/17] x86: Add support for cmpxchg_double Christoph Lameter
2011-06-09  9:53   ` Pekka Enberg
2011-06-10 15:17     ` Christoph Lameter
2011-06-11  9:50       ` Pekka Enberg
2011-06-11 17:02         ` Christoph Lameter
2011-06-14  5:49           ` Pekka Enberg
2011-06-14  8:04             ` Ingo Molnar
2011-06-14 14:04               ` Christoph Lameter
2011-06-14 15:05                 ` H. Peter Anvin
2011-06-15  8:55   ` Tejun Heo
2011-06-15 14:26     ` Christoph Lameter
2011-06-15 16:39       ` Tejun Heo
2011-06-15 17:19         ` Christoph Lameter
2011-06-25 23:49   ` [tip:x86/atomic] " tip-bot for Christoph Lameter
2011-06-01 17:25 ` [slubllv7 05/17] mm: Rearrange struct page Christoph Lameter
2011-06-09  9:57   ` Pekka Enberg
2011-06-09 16:45     ` Andrew Morton [this message]
2011-06-09 17:03       ` [PATCH] checkpatch: Add a "prefer __aligned" check Joe Perches
2011-06-01 17:25 ` [slubllv7 06/17] slub: Add cmpxchg_double_slab() Christoph Lameter
2011-07-11 19:55   ` Eric Dumazet
2011-07-12 15:59     ` Christoph Lameter
2011-07-12 16:06       ` Eric Dumazet
2011-07-12 16:47         ` Christoph Lameter
2011-07-12 18:40           ` H. Peter Anvin
2011-07-12 18:53             ` Christoph Lameter
2011-07-12 20:40               ` H. Peter Anvin
2011-06-01 17:25 ` [slubllv7 07/17] slub: explicit list_lock taking Christoph Lameter
2011-06-01 17:25 ` [slubllv7 08/17] slub: Pass kmem_cache struct to lock and freeze slab Christoph Lameter
2011-06-01 17:25 ` [slubllv7 09/17] slub: Rework allocator fastpaths Christoph Lameter
2011-06-01 17:25 ` [slubllv7 10/17] slub: Invert locking and avoid slab lock Christoph Lameter
2011-06-01 17:25 ` [slubllv7 11/17] slub: Disable interrupts in free_debug processing Christoph Lameter
2011-06-01 17:25 ` [slubllv7 12/17] slub: Avoid disabling interrupts in free slowpath Christoph Lameter
2011-06-01 17:25 ` [slubllv7 13/17] slub: Get rid of the another_slab label Christoph Lameter
2011-06-01 17:25 ` [slubllv7 14/17] slub: Add statistics for the case that the current slab does not match the node Christoph Lameter
2011-06-01 17:25 ` [slubllv7 15/17] slub: fast release on full slab Christoph Lameter
2011-06-01 17:25 ` [slubllv7 16/17] slub: Not necessary to check for empty slab on load_freelist Christoph Lameter
2011-06-01 17:26 ` [slubllv7 17/17] slub: slabinfo update for cmpxchg handling Christoph Lameter

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