From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-la0-f45.google.com (mail-la0-f45.google.com [209.85.215.45]) by kanga.kvack.org (Postfix) with ESMTP id 59A606B0031 for ; Thu, 19 Dec 2013 03:51:49 -0500 (EST) Received: by mail-la0-f45.google.com with SMTP id eh20so324325lab.32 for ; Thu, 19 Dec 2013 00:51:48 -0800 (PST) Received: from relay.parallels.com (relay.parallels.com. [195.214.232.42]) by mx.google.com with ESMTPS id a4si1284565laf.53.2013.12.19.00.51.47 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Thu, 19 Dec 2013 00:51:47 -0800 (PST) Message-ID: <52B2B39A.7070303@parallels.com> Date: Thu, 19 Dec 2013 12:51:38 +0400 From: Vladimir Davydov MIME-Version: 1.0 Subject: Re: [PATCH 1/6] slab: cleanup kmem_cache_create_memcg() References: <6f02b2d079ffd0990ae335339c803337b13ecd8c.1387372122.git.vdavydov@parallels.com> <20131218165603.GB31080@dhcp22.suse.cz> <52B292CF.5030002@parallels.com> <20131219084447.GA9331@dhcp22.suse.cz> In-Reply-To: <20131219084447.GA9331@dhcp22.suse.cz> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, devel@openvz.org, Johannes Weiner , Glauber Costa , Christoph Lameter , Pekka Enberg , Andrew Morton On 12/19/2013 12:44 PM, Michal Hocko wrote: > On Thu 19-12-13 10:31:43, Vladimir Davydov wrote: >> On 12/18/2013 08:56 PM, Michal Hocko wrote: >>> On Wed 18-12-13 17:16:52, Vladimir Davydov wrote: >>>> Signed-off-by: Vladimir Davydov >>>> Cc: Michal Hocko >>>> Cc: Johannes Weiner >>>> Cc: Glauber Costa >>>> Cc: Christoph Lameter >>>> Cc: Pekka Enberg >>>> Cc: Andrew Morton >>> Dunno, is this really better to be worth the code churn? >>> >>> It even makes the generated code tiny bit bigger: >>> text data bss dec hex filename >>> 4355 171 236 4762 129a mm/slab_common.o.after >>> 4342 171 236 4749 128d mm/slab_common.o.before >>> >>> Or does it make the further changes much more easier? Be explicit in the >>> patch description if so. >> Hi, Michal >> >> IMO, undoing under labels looks better than inside conditionals, because >> we don't have to repeat the same deinitialization code then, like this >> (note three calls to kmem_cache_free()): > Agreed but the resulting code is far from doing nice undo on different > conditions. You have out_free_cache which frees everything regardless > whether name or cache registration failed. So it doesn't help with > readability much IMO. AFAIK it's common practice not to split kfree's to be called under different labels on fail paths, because kfree(NULL) results in a no-op. Since on undo, we only call kfree, I introduce the only label. Of course I could do something like s->name=... if (!s->name) goto out_free_name; err = __kmem_new_cache(...) if (err) goto out_free_name; <...> out_free_name: kfree(s->name); out_free_cache: kfree(s); goto out_unlock; But I think using only out_free_cache makes the code look clearer. > >> s = kmem_cache_zalloc(kmem_cache, GFP_KERNEL); >> if (s) { >> s->object_size = s->size = size; >> s->align = calculate_alignment(flags, align, size); >> s->ctor = ctor; >> >> if (memcg_register_cache(memcg, s, parent_cache)) { >> kmem_cache_free(kmem_cache, s); >> err = -ENOMEM; >> goto out_locked; >> } >> >> s->name = kstrdup(name, GFP_KERNEL); >> if (!s->name) { >> kmem_cache_free(kmem_cache, s); >> err = -ENOMEM; >> goto out_locked; >> } >> >> err = __kmem_cache_create(s, flags); >> if (!err) { >> s->refcount = 1; >> list_add(&s->list, &slab_caches); >> memcg_cache_list_add(memcg, s); >> } else { >> kfree(s->name); >> kmem_cache_free(kmem_cache, s); >> } >> } else >> err = -ENOMEM; >> >> The next patch, which fixes the memcg_params leakage on error, would >> make it even worse introducing two calls to memcg_free_cache_params() >> after kstrdup and __kmem_cache_create. >> >> If you think it isn't worthwhile applying this patch, just let me know, >> I don't mind dropping it. > As I've said if it helps with the later patches then I do not mind but > on its own it doesn't sound like a huge improvement. > > Btw. you do not have to set err = -ENOMEM before goto out_locked. Just > set before kmem_cache_zalloc. You also do not need to initialize it to 0 > because kmem_cache_sanity_check will set it. OK, thanks. -- 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