From: Pekka Enberg <penberg@kernel.org>
To: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Seth Jennings <sjenning@linux.vnet.ibm.com>,
Dan Magenheimer <dan.magenheimer@oracle.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
cl@linux-foundation.org
Subject: Re: [PATCH 4/4] zsmalloc: zsmalloc: align cache line size
Date: Mon, 7 May 2012 10:41:45 +0300 (EEST) [thread overview]
Message-ID: <alpine.LFD.2.02.1205071038090.2851@tux.localdomain> (raw)
In-Reply-To: <4FA33E89.6080206@kernel.org>
On Fri, 4 May 2012, Minchan Kim wrote:
> >> It's a overkill to align pool size with PAGE_SIZE to avoid
> >> false-sharing. This patch aligns it with just cache line size.
> >>
> >> Signed-off-by: Minchan Kim<minchan@kernel.org>
> >> ---
> >> drivers/staging/zsmalloc/zsmalloc-main.c | 6 +++---
> >> 1 file changed, 3 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c
> >> b/drivers/staging/zsmalloc/zsmalloc-main.c
> >> index 51074fa..3991b03 100644
> >> --- a/drivers/staging/zsmalloc/zsmalloc-main.c
> >> +++ b/drivers/staging/zsmalloc/zsmalloc-main.c
> >> @@ -489,14 +489,14 @@ fail:
> >>
> >> struct zs_pool *zs_create_pool(const char *name, gfp_t flags)
> >> {
> >> - int i, error, ovhd_size;
> >> + int i, error;
> >> struct zs_pool *pool;
> >>
> >> if (!name)
> >> return NULL;
> >>
> >> - ovhd_size = roundup(sizeof(*pool), PAGE_SIZE);
> >> - pool = kzalloc(ovhd_size, GFP_KERNEL);
> >> + pool = kzalloc(ALIGN(sizeof(*pool), cache_line_size()),
> >> + GFP_KERNEL);
> >
> > a basic question:
> > Is rounding off allocation size to cache_line_size enough to ensure
> > that the object is cache-line-aligned? Isn't it possible that even
> > though the object size is multiple of cache-line, it may still not be
> > properly aligned and end up sharing cache line with some other
> > read-mostly object?
>
> AFAIK, SLAB allocates object aligned cache-size so I think that problem cannot happen.
> But needs double check.
> Cced Pekka.
The kmalloc(size) function only gives you the following guarantees:
(1) The allocated object is _at least_ 'size' bytes.
(2) The returned pointer is aligned to ARCH_KMALLOC_MINALIGN.
Anything beyond that is implementation detail and probably will break if
you switch between SLAB/SLUB/SLOB.
Pekka
next prev parent reply other threads:[~2012-05-07 7:41 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-03 6:40 [PATCH 1/4] zsmalloc: rename zspage_order with zspage_pages Minchan Kim
2012-05-03 6:40 ` [PATCH 2/4] zsmalloc: add/fix function comment Minchan Kim
2012-05-03 13:19 ` Nitin Gupta
2012-05-03 6:40 ` [PATCH 3/4] zsmalloc use zs_handle instead of void * Minchan Kim
2012-05-03 13:32 ` Nitin Gupta
2012-05-03 15:23 ` Seth Jennings
2012-05-04 2:24 ` Minchan Kim
2012-05-07 15:01 ` Seth Jennings
2012-05-09 20:19 ` Greg Kroah-Hartman
2012-05-10 2:03 ` Minchan Kim
2012-05-10 14:02 ` Konrad Rzeszutek Wilk
2012-05-10 14:12 ` Greg Kroah-Hartman
2012-05-10 14:47 ` Nitin Gupta
2012-05-10 15:00 ` Minchan Kim
2012-05-10 15:11 ` Seth Jennings
2012-05-10 15:19 ` Minchan Kim
2012-05-10 15:19 ` Greg Kroah-Hartman
2012-05-10 16:29 ` Nitin Gupta
2012-05-10 16:44 ` Greg Kroah-Hartman
2012-05-10 17:24 ` Nitin Gupta
2012-05-10 17:33 ` Konrad Rzeszutek Wilk
2012-05-10 23:24 ` Minchan Kim
2012-05-10 23:50 ` Dan Magenheimer
2012-05-11 0:14 ` Minchan Kim
2012-05-11 16:31 ` Dan Magenheimer
2012-05-11 19:29 ` Konrad Rzeszutek Wilk
2012-05-11 21:49 ` Seth Jennings
2012-05-14 2:26 ` Minchan Kim
2012-05-11 19:28 ` Konrad Rzeszutek Wilk
2012-05-14 2:18 ` Minchan Kim
2012-05-15 1:57 ` Nitin Gupta
2012-05-15 2:21 ` Minchan Kim
2012-05-15 15:04 ` Konrad Rzeszutek Wilk
2012-05-16 1:36 ` Minchan Kim
2012-05-16 11:06 ` Konrad Rzeszutek Wilk
2012-05-03 6:40 ` [PATCH 4/4] zsmalloc: zsmalloc: align cache line size Minchan Kim
2012-05-03 13:58 ` Nitin Gupta
2012-05-04 2:27 ` Minchan Kim
2012-05-07 7:41 ` Pekka Enberg [this message]
2012-05-07 12:40 ` Nitin Gupta
2012-05-08 1:34 ` Minchan Kim
2012-05-08 14:00 ` Dan Magenheimer
2012-05-09 0:58 ` Minchan Kim
2012-05-09 3:08 ` Dan Magenheimer
2012-05-09 4:07 ` Minchan Kim
2012-05-11 0:03 ` Dan Magenheimer
2012-05-11 0:25 ` Minchan Kim
2012-05-11 19:06 ` Konrad Rzeszutek Wilk
2012-05-14 1:55 ` Minchan Kim
2012-05-15 15:18 ` Konrad Rzeszutek Wilk
2012-05-16 1:44 ` Minchan Kim
2012-05-03 13:18 ` [PATCH 1/4] zsmalloc: rename zspage_order with zspage_pages Nitin Gupta
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