From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx192.postini.com [74.125.245.192]) by kanga.kvack.org (Postfix) with SMTP id B7F876B0044 for ; Thu, 3 May 2012 22:27:23 -0400 (EDT) Message-ID: <4FA33E89.6080206@kernel.org> Date: Fri, 04 May 2012 11:27:21 +0900 From: Minchan Kim MIME-Version: 1.0 Subject: Re: [PATCH 4/4] zsmalloc: zsmalloc: align cache line size References: <1336027242-372-1-git-send-email-minchan@kernel.org> <1336027242-372-4-git-send-email-minchan@kernel.org> <4FA28EFD.5070002@vflare.org> In-Reply-To: <4FA28EFD.5070002@vflare.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Nitin Gupta Cc: Greg Kroah-Hartman , Seth Jennings , Dan Magenheimer , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Pekka Enberg On 05/03/2012 10:58 PM, Nitin Gupta wrote: > On 5/3/12 2:40 AM, 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 >> --- >> 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. > > Thanks, > Nitin > > >> if (!pool) >> return NULL; >> > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Fight unfair telecom internet charges in Canada: sign > http://stopthemeter.ca/ > Don't email: email@kvack.org > -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org