From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vasily Averin Subject: Re: [Devel] [PATCH 1/6] slab: cleanup kmem_cache_create_memcg() Date: Thu, 19 Dec 2013 13:26:12 +0400 Message-ID: <52B2BBB4.3090209@parallels.com> References: <6f02b2d079ffd0990ae335339c803337b13ecd8c.1387372122.git.vdavydov@parallels.com> <52B2AB7C.1010803@parallels.com> <52B2B0A4.8050009@parallels.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <52B2B0A4.8050009-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Vladimir Davydov Cc: Michal Hocko , Glauber Costa , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Pekka Enberg , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Johannes Weiner , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Christoph Lameter , Andrew Morton , devel-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org On 12/19/2013 12:39 PM, Vladimir Davydov wrote: > On 12/19/2013 12:17 PM, Vasily Averin wrote: >> On 12/18/2013 05:16 PM, Vladimir Davydov wrote: >>> --- a/mm/slab_common.c >>> +++ b/mm/slab_common.c >>> @@ -176,8 +176,9 @@ kmem_cache_create_memcg(struct mem_cgroup *memcg, const char *name, size_t size, >>> get_online_cpus(); >>> mutex_lock(&slab_mutex); >>> >>> - if (!kmem_cache_sanity_check(memcg, name, size) == 0) >>> - goto out_locked; >>> + err = kmem_cache_sanity_check(memcg, name, size); >>> + if (err) >>> + goto out_unlock; >>> >>> /* >>> * Some allocators will constraint the set of valid flags to a subset >> Theoretically in future kmem_cache_sanity_check() can return positive value. >> Probably it's better to check (err < 0) in caller ? > > Hmm, why? What information could positive retval carry here? We have > plenty of places throughout the code where we check for (err), not > (err<0), simply because it looks clearer, e.g. look at > __kmem_cache_create() calls. If it returns a positive value one day, we > will have to parse every place where it's called. Anyway, if someone > wants to change a function behavior, he must check every place where > this function is called and fix them accordingly. I believe expected semantic of function -- return negative in case of error. So correct error cheek should be (err < 0). (err) check is semantically incorrect, and it can lead to troubles in future. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f182.google.com (mail-ig0-f182.google.com [209.85.213.182]) by kanga.kvack.org (Postfix) with ESMTP id 129D36B0039 for ; Thu, 19 Dec 2013 04:26:58 -0500 (EST) Received: by mail-ig0-f182.google.com with SMTP id c10so3489580igq.3 for ; Thu, 19 Dec 2013 01:26:57 -0800 (PST) Received: from relay.sw.ru (mailhub.sw.ru. [195.214.232.25]) by mx.google.com with ESMTPS id jw1si3133904icc.36.2013.12.19.01.26.55 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Thu, 19 Dec 2013 01:26:56 -0800 (PST) Message-ID: <52B2BBB4.3090209@parallels.com> Date: Thu, 19 Dec 2013 13:26:12 +0400 From: Vasily Averin MIME-Version: 1.0 Subject: Re: [Devel] [PATCH 1/6] slab: cleanup kmem_cache_create_memcg() References: <6f02b2d079ffd0990ae335339c803337b13ecd8c.1387372122.git.vdavydov@parallels.com> <52B2AB7C.1010803@parallels.com> <52B2B0A4.8050009@parallels.com> In-Reply-To: <52B2B0A4.8050009@parallels.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Vladimir Davydov Cc: Michal Hocko , Glauber Costa , linux-kernel@vger.kernel.org, Pekka Enberg , linux-mm@kvack.org, Johannes Weiner , cgroups@vger.kernel.org, Christoph Lameter , Andrew Morton , devel@openvz.org On 12/19/2013 12:39 PM, Vladimir Davydov wrote: > On 12/19/2013 12:17 PM, Vasily Averin wrote: >> On 12/18/2013 05:16 PM, Vladimir Davydov wrote: >>> --- a/mm/slab_common.c >>> +++ b/mm/slab_common.c >>> @@ -176,8 +176,9 @@ kmem_cache_create_memcg(struct mem_cgroup *memcg, const char *name, size_t size, >>> get_online_cpus(); >>> mutex_lock(&slab_mutex); >>> >>> - if (!kmem_cache_sanity_check(memcg, name, size) == 0) >>> - goto out_locked; >>> + err = kmem_cache_sanity_check(memcg, name, size); >>> + if (err) >>> + goto out_unlock; >>> >>> /* >>> * Some allocators will constraint the set of valid flags to a subset >> Theoretically in future kmem_cache_sanity_check() can return positive value. >> Probably it's better to check (err < 0) in caller ? > > Hmm, why? What information could positive retval carry here? We have > plenty of places throughout the code where we check for (err), not > (err<0), simply because it looks clearer, e.g. look at > __kmem_cache_create() calls. If it returns a positive value one day, we > will have to parse every place where it's called. Anyway, if someone > wants to change a function behavior, he must check every place where > this function is called and fix them accordingly. I believe expected semantic of function -- return negative in case of error. So correct error cheek should be (err < 0). (err) check is semantically incorrect, and it can lead to troubles in future. -- 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/ . Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752137Ab3LSJ1J (ORCPT ); Thu, 19 Dec 2013 04:27:09 -0500 Received: from mailhub.sw.ru ([195.214.232.25]:43053 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751075Ab3LSJ1H (ORCPT ); Thu, 19 Dec 2013 04:27:07 -0500 Message-ID: <52B2BBB4.3090209@parallels.com> Date: Thu, 19 Dec 2013 13:26:12 +0400 From: Vasily Averin Organization: Parallels User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130329 Thunderbird/17.0.5 MIME-Version: 1.0 To: Vladimir Davydov CC: Michal Hocko , Glauber Costa , linux-kernel@vger.kernel.org, Pekka Enberg , linux-mm@kvack.org, Johannes Weiner , cgroups@vger.kernel.org, Christoph Lameter , Andrew Morton , devel@openvz.org Subject: Re: [Devel] [PATCH 1/6] slab: cleanup kmem_cache_create_memcg() References: <6f02b2d079ffd0990ae335339c803337b13ecd8c.1387372122.git.vdavydov@parallels.com> <52B2AB7C.1010803@parallels.com> <52B2B0A4.8050009@parallels.com> In-Reply-To: <52B2B0A4.8050009@parallels.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/19/2013 12:39 PM, Vladimir Davydov wrote: > On 12/19/2013 12:17 PM, Vasily Averin wrote: >> On 12/18/2013 05:16 PM, Vladimir Davydov wrote: >>> --- a/mm/slab_common.c >>> +++ b/mm/slab_common.c >>> @@ -176,8 +176,9 @@ kmem_cache_create_memcg(struct mem_cgroup *memcg, const char *name, size_t size, >>> get_online_cpus(); >>> mutex_lock(&slab_mutex); >>> >>> - if (!kmem_cache_sanity_check(memcg, name, size) == 0) >>> - goto out_locked; >>> + err = kmem_cache_sanity_check(memcg, name, size); >>> + if (err) >>> + goto out_unlock; >>> >>> /* >>> * Some allocators will constraint the set of valid flags to a subset >> Theoretically in future kmem_cache_sanity_check() can return positive value. >> Probably it's better to check (err < 0) in caller ? > > Hmm, why? What information could positive retval carry here? We have > plenty of places throughout the code where we check for (err), not > (err<0), simply because it looks clearer, e.g. look at > __kmem_cache_create() calls. If it returns a positive value one day, we > will have to parse every place where it's called. Anyway, if someone > wants to change a function behavior, he must check every place where > this function is called and fix them accordingly. I believe expected semantic of function -- return negative in case of error. So correct error cheek should be (err < 0). (err) check is semantically incorrect, and it can lead to troubles in future.