From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 95159C433ED for ; Tue, 27 Apr 2021 07:53:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5EE6761154 for ; Tue, 27 Apr 2021 07:53:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234845AbhD0HyY (ORCPT ); Tue, 27 Apr 2021 03:54:24 -0400 Received: from mx2.suse.de ([195.135.220.15]:42528 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230062AbhD0HyX (ORCPT ); Tue, 27 Apr 2021 03:54:23 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1619510019; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=KnRuIjNauYv+n59UfyiM6hQaRIw+vg7KJ4k1CdGuSNU=; b=UeG9qa8Rh09mqzLVtdctEr1ik4OVKl5f4APZ9prRrftYqWyQe/MoeKd0kV3eJpox00XdQ9 bBWkoUg2ERcSc8yampmR1B/2WbZoDwqO4/0MsNF0OLIsm6dYHLVmIafN8HVtFDulJiTvz5 NM6heP8S4mO7xp95kWEhVGngoLwObZA= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 4A8FEAFF8; Tue, 27 Apr 2021 07:53:39 +0000 (UTC) Date: Tue, 27 Apr 2021 09:53:38 +0200 From: Michal Hocko To: Alexander Sosna Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] Prevent OOM casualties by enforcing memcg limits Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 26-04-21 22:04:56, Alexander Sosna wrote: > Before this commit memory cgroup limits were not enforced during > allocation. If a process within a cgroup tries to allocates more > memory than allowed, the kernel will not prevent the allocation even if > OVERCOMMIT_NEVER is set. Than the OOM killer is activated to kill > processes in the corresponding cgroup. This behavior is not to be expected > when setting OVERCOMMIT_NEVER (vm.overcommit_memory = 2) and it is a huge > problem for applications assuming that the kernel will deny an allocation > if not enough memory is available, like PostgreSQL. Memory cgroup controller is by design accounting physically allocated memory while overcommit policy is a global control of the virtual memory allocation. Memcg is not aware of the virtual memory commitment so it cannot really evaluate OVERCOMMIT_NEVER heuristic. > To prevent this a > check is implemented to not allow a process to allocate more memory than > limited by it's cgroup. This means a process will not be killed while > accessing pages but will receive errors on memory allocation as > appropriate. This gives programs a chance to handle memory allocation > failures gracefully instead of being reaped. I am afraid I have to nak this patch. It is changing a long term semantic of a user interface which can break many existing applications. So you would need to create a new overcommit mode which would be explicitly memcg aware. As mentioned above memcg would need to have some awareness of the virtual memory committed for the memcg. Without that OVERCOMMIT_NEVER_MEMCG would effectively turn into OVERCOMMIT_GUESS. > Signed-off-by: Alexander Sosna Nacked-by: Michal Hocko > diff --git a/mm/util.c b/mm/util.c > index a8bf17f18a81..c84b83c532c6 100644 > --- a/mm/util.c > +++ b/mm/util.c > @@ -853,6 +853,7 @@ EXPORT_SYMBOL_GPL(vm_memory_committed); > * > * Strict overcommit modes added 2002 Feb 26 by Alan Cox. > * Additional code 2002 Jul 20 by Robert Love. > + * Code to enforce memory cgroup limits added 2021 by Alexander Sosna. > * > * cap_sys_admin is 1 if the process has admin privileges, 0 otherwise. > * > @@ -891,6 +892,34 @@ int __vm_enough_memory(struct mm_struct *mm, long > pages, int cap_sys_admin) > long reserve = sysctl_user_reserve_kbytes >> (PAGE_SHIFT - 10); > > allowed -= min_t(long, mm->total_vm / 32, reserve); > + > +#ifdef CONFIG_MEMCG > + /* > + * If we are in a memory cgroup we also evaluate if the cgroup > + * has enough memory to allocate a new virtual mapping. > + * This is how we can keep processes from exceeding their > + * limits and also prevent that the OOM killer must be > + * awakened. This gives programs a chance to handle memory > + * allocation failures gracefully and not being reaped. > + * In the current version mem_cgroup_get_max() is used which > + * allows the processes to exceeded their memory limits if > + * enough SWAP is available. If this is not intended we could > + * use READ_ONCE(memcg->memory.max) instead. > + * > + * This code is only reached if sysctl_overcommit_memory equals > + * OVERCOMMIT_NEVER, both other options are handled above. > + */ > + { > + struct mem_cgroup *memcg = get_mem_cgroup_from_mm(mm); > + > + if (memcg) { > + long available = mem_cgroup_get_max(memcg) > + - mem_cgroup_size(memcg); > + > + allowed = min_t(long, available, allowed); > + } > + } > +#endif > } > > if (percpu_counter_read_positive(&vm_committed_as) < allowed) -- Michal Hocko SUSE Labs