From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx206.postini.com [74.125.245.206]) by kanga.kvack.org (Postfix) with SMTP id BD5466B004D for ; Thu, 3 May 2012 01:16:12 -0400 (EDT) Received: by qcsd16 with SMTP id d16so1164836qcs.14 for ; Wed, 02 May 2012 22:16:11 -0700 (PDT) Message-ID: <4FA2149A.9030803@vflare.org> Date: Thu, 03 May 2012 01:16:10 -0400 From: Nitin Gupta MIME-Version: 1.0 Subject: Re: [PATCH 2/6] zsmalloc: remove unnecessary alignment References: <1335334994-22138-1-git-send-email-minchan@kernel.org> <1335334994-22138-3-git-send-email-minchan@kernel.org> <4F97F3D6.8000404@vflare.org> <4F98A818.1080106@kernel.org> In-Reply-To: <4F98A818.1080106@kernel.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Minchan Kim Cc: Greg Kroah-Hartman , Seth Jennings , Dan Magenheimer , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org Hi Minchan, Sorry for late reply. On 4/25/12 9:42 PM, Minchan Kim wrote: > On 04/25/2012 09:53 PM, Nitin Gupta wrote: > >> On 04/25/2012 02:23 AM, Minchan Kim wrote: >> >>> It isn't necessary to align pool size with PAGE_SIZE. >>> If I missed something, please let me know it. >>> >>> Signed-off-by: Minchan Kim >>> --- >>> drivers/staging/zsmalloc/zsmalloc-main.c | 5 ++--- >>> 1 file changed, 2 insertions(+), 3 deletions(-) >>> >>> diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c b/drivers/staging/zsmalloc/zsmalloc-main.c >>> index 504b6c2..b99ad9e 100644 >>> --- a/drivers/staging/zsmalloc/zsmalloc-main.c >>> +++ b/drivers/staging/zsmalloc/zsmalloc-main.c >>> @@ -489,14 +489,13 @@ 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(sizeof(*pool), GFP_KERNEL); >>> if (!pool) >>> return NULL; >>> >> >> >> pool metadata is rounded-up to avoid potential false-sharing problem >> (though we could just roundup to cache_line_size()). > > > Do you really have any hurt by false-sharing problem? > If so, we can change it with > I've never been hit by this false-sharing in any testing but this is really just a random chance. Apart from aligning to cache-line size, there is no way to ensure some unfortunate read-mostly object never falls in the same line. > kzalloc(ALIGN(sizeof(*pool), cache_line_size()), GFP_KERNEL); > Yes, looks better than aligning to PAGE_SIZE. Thanks, Nitin -- 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