From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f49.google.com (mail-pa0-f49.google.com [209.85.220.49]) by kanga.kvack.org (Postfix) with ESMTP id CD2B16B0036 for ; Thu, 19 Dec 2013 05:23:47 -0500 (EST) Received: by mail-pa0-f49.google.com with SMTP id kx10so969848pab.8 for ; Thu, 19 Dec 2013 02:23:47 -0800 (PST) Received: from out2-smtp.messagingengine.com (out2-smtp.messagingengine.com. [66.111.4.26]) by mx.google.com with ESMTPS id sa6si2245154pbb.143.2013.12.19.02.23.45 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 19 Dec 2013 02:23:46 -0800 (PST) Message-ID: <52B2C92D.2020301@iki.fi> Date: Thu, 19 Dec 2013 12:23:41 +0200 From: Pekka Enberg 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> <52B2BBB4.3090209@parallels.com> In-Reply-To: <52B2BBB4.3090209@parallels.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Vasily Averin , 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 11:26 AM, Vasily Averin wrote: > 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. I don't know what semantics you are referring to but a typical convention in mm/*.c is to return zero on success and negative on error but never positive numbers. Looking at mm/slab_common.c, "if (err)" is the established convention so using "if (err < 0)" just because is pointless here. Pekka -- 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