From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vladimir Davydov Subject: Re: [PATCH 0/5] memcg/kmem: switch to white list policy Date: Mon, 9 Nov 2015 23:12:18 +0300 Message-ID: <20151109201218.GP31308@esperanza> References: <20151109140832.GE8916@dhcp22.suse.cz> <20151109182840.GJ31308@esperanza> <20151109185401.GB28507@mtj.duckdns.org> <20151109192747.GN31308@esperanza> <20151109193253.GC28507@mtj.duckdns.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Return-path: Content-Disposition: inline In-Reply-To: <20151109193253.GC28507-qYNAdHglDFBN0TnZuCh8vA@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Transfer-Encoding: 7bit To: Tejun Heo Cc: Michal Hocko , Andrew Morton , Johannes Weiner , Greg Thelen , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org On Mon, Nov 09, 2015 at 02:32:53PM -0500, Tejun Heo wrote: > On Mon, Nov 09, 2015 at 10:27:47PM +0300, Vladimir Davydov wrote: > > Of course, we could rework slab merging so that kmem_cache_create > > returned a new dummy cache even if it was actually merged. Such a cache > > would point to the real cache, which would be used for allocations. This > > wouldn't limit slab merging, but this would add one more dereference to > > alloc path, which is even worse. > > Hmmm, this could be me not really understanding but why can't we let > all slabs to be merged regardless of SLAB_ACCOUNT flag for root memcg > and point to per-memcg slabs (may be merged among them but most likely Because we won't be able to distinguish kmem_cache_alloc calls that should be accounted from those that shouldn't. The problem is if two caches A = kmem_cache_create(...) and B = kmem_cache_create(...) happen to be merged, A and B will point to the same kmem_cache struct. As a result, there is no way to distinguish kmem_cache_alloc(A) which we want to account from kmem_cache_alloc(B) which we don't. > won't matter) for !root. We're indirecting once anyway, no? If kmem accounting is not used, we aren't indirecting. That's why I don't think we can use dummy kmem_cache struct for merged caches, where we could store __GFP_ACCOUNT flag. Thanks, Vladimir From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f52.google.com (mail-pa0-f52.google.com [209.85.220.52]) by kanga.kvack.org (Postfix) with ESMTP id 9A7216B0256 for ; Mon, 9 Nov 2015 15:12:28 -0500 (EST) Received: by pacdm15 with SMTP id dm15so184922635pac.3 for ; Mon, 09 Nov 2015 12:12:28 -0800 (PST) Received: from mx2.parallels.com (mx2.parallels.com. [199.115.105.18]) by mx.google.com with ESMTPS id pp8si24395059pbc.2.2015.11.09.12.12.27 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 09 Nov 2015 12:12:27 -0800 (PST) Date: Mon, 9 Nov 2015 23:12:18 +0300 From: Vladimir Davydov Subject: Re: [PATCH 0/5] memcg/kmem: switch to white list policy Message-ID: <20151109201218.GP31308@esperanza> References: <20151109140832.GE8916@dhcp22.suse.cz> <20151109182840.GJ31308@esperanza> <20151109185401.GB28507@mtj.duckdns.org> <20151109192747.GN31308@esperanza> <20151109193253.GC28507@mtj.duckdns.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20151109193253.GC28507@mtj.duckdns.org> Sender: owner-linux-mm@kvack.org List-ID: To: Tejun Heo Cc: Michal Hocko , Andrew Morton , Johannes Weiner , Greg Thelen , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org On Mon, Nov 09, 2015 at 02:32:53PM -0500, Tejun Heo wrote: > On Mon, Nov 09, 2015 at 10:27:47PM +0300, Vladimir Davydov wrote: > > Of course, we could rework slab merging so that kmem_cache_create > > returned a new dummy cache even if it was actually merged. Such a cache > > would point to the real cache, which would be used for allocations. This > > wouldn't limit slab merging, but this would add one more dereference to > > alloc path, which is even worse. > > Hmmm, this could be me not really understanding but why can't we let > all slabs to be merged regardless of SLAB_ACCOUNT flag for root memcg > and point to per-memcg slabs (may be merged among them but most likely Because we won't be able to distinguish kmem_cache_alloc calls that should be accounted from those that shouldn't. The problem is if two caches A = kmem_cache_create(...) and B = kmem_cache_create(...) happen to be merged, A and B will point to the same kmem_cache struct. As a result, there is no way to distinguish kmem_cache_alloc(A) which we want to account from kmem_cache_alloc(B) which we don't. > won't matter) for !root. We're indirecting once anyway, no? If kmem accounting is not used, we aren't indirecting. That's why I don't think we can use dummy kmem_cache struct for merged caches, where we could store __GFP_ACCOUNT flag. Thanks, Vladimir -- 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 S1752395AbbKIUMa (ORCPT ); Mon, 9 Nov 2015 15:12:30 -0500 Received: from mx2.parallels.com ([199.115.105.18]:54035 "EHLO mx2.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751535AbbKIUM2 (ORCPT ); Mon, 9 Nov 2015 15:12:28 -0500 Date: Mon, 9 Nov 2015 23:12:18 +0300 From: Vladimir Davydov To: Tejun Heo CC: Michal Hocko , Andrew Morton , Johannes Weiner , Greg Thelen , , , Subject: Re: [PATCH 0/5] memcg/kmem: switch to white list policy Message-ID: <20151109201218.GP31308@esperanza> References: <20151109140832.GE8916@dhcp22.suse.cz> <20151109182840.GJ31308@esperanza> <20151109185401.GB28507@mtj.duckdns.org> <20151109192747.GN31308@esperanza> <20151109193253.GC28507@mtj.duckdns.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20151109193253.GC28507@mtj.duckdns.org> X-ClientProxiedBy: US-EXCH.sw.swsoft.com (10.255.249.47) To US-EXCH2.sw.swsoft.com (10.255.249.46) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 09, 2015 at 02:32:53PM -0500, Tejun Heo wrote: > On Mon, Nov 09, 2015 at 10:27:47PM +0300, Vladimir Davydov wrote: > > Of course, we could rework slab merging so that kmem_cache_create > > returned a new dummy cache even if it was actually merged. Such a cache > > would point to the real cache, which would be used for allocations. This > > wouldn't limit slab merging, but this would add one more dereference to > > alloc path, which is even worse. > > Hmmm, this could be me not really understanding but why can't we let > all slabs to be merged regardless of SLAB_ACCOUNT flag for root memcg > and point to per-memcg slabs (may be merged among them but most likely Because we won't be able to distinguish kmem_cache_alloc calls that should be accounted from those that shouldn't. The problem is if two caches A = kmem_cache_create(...) and B = kmem_cache_create(...) happen to be merged, A and B will point to the same kmem_cache struct. As a result, there is no way to distinguish kmem_cache_alloc(A) which we want to account from kmem_cache_alloc(B) which we don't. > won't matter) for !root. We're indirecting once anyway, no? If kmem accounting is not used, we aren't indirecting. That's why I don't think we can use dummy kmem_cache struct for merged caches, where we could store __GFP_ACCOUNT flag. Thanks, Vladimir