From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [PATCH] memcg: remove KMEM_ACCOUNTED_ACTIVATED Date: Mon, 2 Dec 2013 19:15:01 +0100 Message-ID: <20131202181501.GA5524@dhcp22.suse.cz> References: <1385989693-28788-1-git-send-email-vdavydov@parallels.com> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; bh=gtl0W8KjQsS+rLkdy1r7N0Da/rMT8NHiNfnmRJnBA0k=; b=svtPKRYW83pD4YGHIHUSsdbWSdgf+1IHx9HIo1fZ8M+trfH5pr0H+2Ydm/DkO6f6hX hEtPiuSIk8CLmQr81ZsjNipHSEMi9pgkUbGnTylVJBv/J+8XVXlJtun85XD05WT/AU6o i52Xp4icQfK/gKnR+82ry3uUi4lAW3dZ6EAJqcgmfsN147iqkLmmm4XLNOTnSwUlBt0l oipgt8QEGthnnYifXYPAsCmgIBJOp+y3/a046YJ/t2ZMYqu158EJv9wjwkqI7DNzKjdW WHR5cYhdNQdOIJPthNheTlS8S02lTuVJ3fDvTkNfiPXxpNb0PI0WhkPdtns8nqNvsx/r AapA== Content-Disposition: inline In-Reply-To: <1385989693-28788-1-git-send-email-vdavydov-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Vladimir Davydov Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, devel-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org, Johannes Weiner , Balbir Singh , KAMEZAWA Hiroyuki , Glauber Costa [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. 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-u79uwXL29TY76Z2rM5mHXA@public.gmane.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Michal Hocko SUSE Labs