Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754430AbbEZRWl (ORCPT ); Tue, 26 May 2015 13:22:41 -0400 Received: from mail-wg0-f51.google.com ([74.125.82.51]:34229 "EHLO mail-wg0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752353AbbEZRWh (ORCPT ); Tue, 26 May 2015 13:22:37 -0400 Date: Tue, 26 May 2015 19:22:34 +0200 From: Michal Hocko To: Oleg Nesterov Cc: linux-mm@kvack.org, Johannes Weiner , Tejun Heo , Vladimir Davydov , KAMEZAWA Hiroyuki , KOSAKI Motohiro , Andrew Morton , LKML Subject: Re: [RFC 3/3] memcg: get rid of mm_struct::owner Message-ID: <20150526172234.GK14681@dhcp22.suse.cz> References: <1432641006-8025-1-git-send-email-mhocko@suse.cz> <1432641006-8025-4-git-send-email-mhocko@suse.cz> <20150526163646.GA29968@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150526163646.GA29968@redhat.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2653 Lines: 80 On Tue 26-05-15 18:36:46, Oleg Nesterov wrote: > On 05/26, Michal Hocko wrote: > > > > @@ -426,17 +426,7 @@ struct mm_struct { > > struct kioctx_table __rcu *ioctx_table; > > #endif > > #ifdef CONFIG_MEMCG > > - /* > > - * "owner" points to a task that is regarded as the canonical > > - * user/owner of this mm. All of the following must be true in > > - * order for it to be changed: > > - * > > - * current == mm->owner > > - * current->mm != mm > > - * new_owner->mm == mm > > - * new_owner->alloc_lock is held > > - */ > > - struct task_struct __rcu *owner; > > + struct mem_cgroup __rcu *memcg; > > Yes, thanks, this is what I tried to suggest ;) > > But I can't review this series. Simply because I know nothing about > memcs. I don't even know how to use it. > > Just one question, > > > +static struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p) > > +{ > > + if (!p->mm) > > + return NULL; > > + return rcu_dereference(p->mm->memcg); > > +} > > Probably I missed something, but it seems that the callers do not > expect it can return NULL. This hasn't changed by this patch. mem_cgroup_from_task was allowed to return NULL even before. I've just made it static because it doesn't have any external users anymore. I will double check whether we can ever get NULL there in the real life. We have this code like that for quite some time. Maybe this is just a heritage from the past... > Perhaps sock_update_memcg() is fine, but > task_in_mem_cgroup() calls it when find_lock_task_mm() fails, and in > this case ->mm is NULL. > > And in fact I can't understand what mem_cgroup_from_task() actually > means, with or without these changes. It performs task_struct->mem_cgroup mapping. We cannot use cgroup mapping here because the charges are bound to mm_struct rather than task. > And another question. I can't understand what happens when a task > execs... IOW, could you confirm that exec_mmap() does not need > mm_set_memcg(mm, oldmm->memcg) ? Right you are! Fixed thanks! --- diff --git a/fs/exec.c b/fs/exec.c index 2cd4def4b1d6..ea00d5a47aad 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -867,6 +867,7 @@ static int exec_mmap(struct mm_struct *mm) up_read(&old_mm->mmap_sem); BUG_ON(active_mm != old_mm); setmax_mm_hiwater_rss(&tsk->signal->maxrss, old_mm); + mm_set_memcg(mm, old_mm->memcg); mmput(old_mm); return 0; } -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/