From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759571Ab3LBVSR (ORCPT ); Mon, 2 Dec 2013 16:18:17 -0500 Received: from relay.parallels.com ([195.214.232.42]:52334 "EHLO relay.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753671Ab3LBTMv (ORCPT ); Mon, 2 Dec 2013 14:12:51 -0500 Message-ID: <529CDBAB.8060307@parallels.com> Date: Mon, 2 Dec 2013 23:12:43 +0400 From: Vladimir Davydov User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130922 Icedove/17.0.9 MIME-Version: 1.0 To: Michal Hocko CC: , , , Johannes Weiner , Balbir Singh , KAMEZAWA Hiroyuki , Glauber Costa Subject: Re: [PATCH] memcg: remove KMEM_ACCOUNTED_ACTIVATED References: <1385989693-28788-1-git-send-email-vdavydov@parallels.com> <20131202181501.GA5524@dhcp22.suse.cz> In-Reply-To: <20131202181501.GA5524@dhcp22.suse.cz> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.24.25.12] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/02/2013 10:15 PM, Michal Hocko wrote: > [CCing Glauber - please do so in other posts for kmem related changes] > > On Mon 02-12-13 17:08:13, Vladimir Davydov wrote: >> The KMEM_ACCOUNTED_ACTIVATED was introduced by commit a8964b9b ("memcg: >> use static branches when code not in use") in order to guarantee that >> static_key_slow_inc(&memcg_kmem_enabled_key) will be called only once >> for each memory cgroup when its kmem limit is set. The point is that at >> that time the memcg_update_kmem_limit() function's workflow looked like >> this: >> >> bool must_inc_static_branch = false; >> >> cgroup_lock(); >> mutex_lock(&set_limit_mutex); >> if (!memcg->kmem_account_flags && val != RESOURCE_MAX) { >> /* The kmem limit is set for the first time */ >> ret = res_counter_set_limit(&memcg->kmem, val); >> >> memcg_kmem_set_activated(memcg); >> must_inc_static_branch = true; >> } else >> ret = res_counter_set_limit(&memcg->kmem, val); >> mutex_unlock(&set_limit_mutex); >> cgroup_unlock(); >> >> if (must_inc_static_branch) { >> /* We can't do this under cgroup_lock */ >> static_key_slow_inc(&memcg_kmem_enabled_key); >> memcg_kmem_set_active(memcg); >> } >> >> Today, we don't use cgroup_lock in memcg_update_kmem_limit(), and >> static_key_slow_inc() is called under the set_limit_mutex, but the >> leftover from the above-mentioned commit is still here. Let's remove it. > OK, so I have looked there again and 692e89abd154b (memcg: increment > static branch right after limit set) which went in after cgroup_mutex > has been removed. It came along with the following comment. > /* > * setting the active bit after the inc will guarantee no one > * starts accounting before all call sites are patched > */ > > This suggests that the flag is needed after all because we have > to be sure that _all_ the places have to be patched. AFAIU > memcg_kmem_newpage_charge might see the static key already patched so > it would do a charge but memcg_kmem_commit_charge would still see it > unpatched and so the charge won't be committed. Hmm, but we have the KMEM_ACCOUNTED_ACTIVE flag, which is set *after* static_key_slow_inc() in memcg_update_kmem_limit(), and __memcg_kmem_newpage_charge() checks it before charging (memcg_can_account_kmem()). So the situation you described is impossible? > > Or am I missing something? > >> Signed-off-by: Vladimir Davydov >> Cc: Johannes Weiner >> Cc: Michal Hocko >> Cc: Balbir Singh >> Cc: KAMEZAWA Hiroyuki >> --- >> mm/memcontrol.c | 26 +------------------------- >> 1 file changed, 1 insertion(+), 25 deletions(-) >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index f1a0ae6..f78661f 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -344,14 +344,9 @@ static size_t memcg_size(void) >> /* internal only representation about the status of kmem accounting. */ >> enum { >> KMEM_ACCOUNTED_ACTIVE = 0, /* accounted by this cgroup itself */ >> - KMEM_ACCOUNTED_ACTIVATED, /* static key enabled. */ >> KMEM_ACCOUNTED_DEAD, /* dead memcg with pending kmem charges */ >> }; >> >> -/* We account when limit is on, but only after call sites are patched */ >> -#define KMEM_ACCOUNTED_MASK \ >> - ((1 << KMEM_ACCOUNTED_ACTIVE) | (1 << KMEM_ACCOUNTED_ACTIVATED)) >> - >> #ifdef CONFIG_MEMCG_KMEM >> static inline void memcg_kmem_set_active(struct mem_cgroup *memcg) >> { >> @@ -363,16 +358,6 @@ static bool memcg_kmem_is_active(struct mem_cgroup *memcg) >> return test_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_account_flags); >> } >> >> -static void memcg_kmem_set_activated(struct mem_cgroup *memcg) >> -{ >> - set_bit(KMEM_ACCOUNTED_ACTIVATED, &memcg->kmem_account_flags); >> -} >> - >> -static void memcg_kmem_clear_activated(struct mem_cgroup *memcg) >> -{ >> - clear_bit(KMEM_ACCOUNTED_ACTIVATED, &memcg->kmem_account_flags); >> -} >> - >> static void memcg_kmem_mark_dead(struct mem_cgroup *memcg) >> { >> /* >> @@ -2956,7 +2941,7 @@ static DEFINE_MUTEX(set_limit_mutex); >> static inline bool memcg_can_account_kmem(struct mem_cgroup *memcg) >> { >> return !mem_cgroup_disabled() && !mem_cgroup_is_root(memcg) && >> - (memcg->kmem_account_flags & KMEM_ACCOUNTED_MASK); >> + memcg_kmem_is_active(memcg); >> } >> >> /* >> @@ -3091,19 +3076,10 @@ int memcg_update_cache_sizes(struct mem_cgroup *memcg) >> 0, MEMCG_CACHES_MAX_SIZE, GFP_KERNEL); >> if (num < 0) >> return num; >> - /* >> - * After this point, kmem_accounted (that we test atomically in >> - * the beginning of this conditional), is no longer 0. This >> - * guarantees only one process will set the following boolean >> - * to true. We don't need test_and_set because we're protected >> - * by the set_limit_mutex anyway. >> - */ >> - memcg_kmem_set_activated(memcg); >> >> ret = memcg_update_all_caches(num+1); >> if (ret) { >> ida_simple_remove(&kmem_limited_groups, num); >> - memcg_kmem_clear_activated(memcg); >> return ret; >> } >> >> -- >> 1.7.10.4 >> >> -- >> To unsubscribe from this list: send the line "unsubscribe cgroups" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html