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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_MUTT 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 B6190C48BE3 for ; Thu, 20 Jun 2019 15:35:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 906D22083B for ; Thu, 20 Jun 2019 15:35:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1561044921; bh=RzqcfmIOU09qV/zj5/we/P4b1oQKWWZQlrj7DOQbg7k=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=P/s4Y2X+KtmE25X12UQRE1Cmv5ysdoIAiuJ/6psYNSCaspgOgLreSgQUofdc40ru7 petpIf1elUKgV4oJ8frG8pRGgBZGbsly27Wffe3ecfEE3d1JwMIShcN7DjTw7EjXop 7PhdqTVQ44JO9DBE1gdCfej9v+akUSa0a0hp/Gxk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727552AbfFTPfU (ORCPT ); Thu, 20 Jun 2019 11:35:20 -0400 Received: from mx2.suse.de ([195.135.220.15]:41364 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726757AbfFTPfT (ORCPT ); Thu, 20 Jun 2019 11:35:19 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 1977EAE46; Thu, 20 Jun 2019 15:35:18 +0000 (UTC) Date: Thu, 20 Jun 2019 17:35:16 +0200 From: Michal Hocko To: Shakeel Butt Cc: Johannes Weiner , Christoph Lameter , Andrew Morton , Roman Gushchin , Pekka Enberg , David Rientjes , Joonsoo Kim , Cgroups , Linux MM , LKML , Dave Hansen Subject: Re: [PATCH] slub: Don't panic for memcg kmem cache creation failure Message-ID: <20190620153516.GG12083@dhcp22.suse.cz> References: <20190619232514.58994-1-shakeelb@google.com> <20190620055028.GA12083@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 20-06-19 07:44:27, Shakeel Butt wrote: > On Wed, Jun 19, 2019 at 10:50 PM Michal Hocko wrote: > > > > On Wed 19-06-19 16:25:14, Shakeel Butt wrote: > > > Currently for CONFIG_SLUB, if a memcg kmem cache creation is failed and > > > the corresponding root kmem cache has SLAB_PANIC flag, the kernel will > > > be crashed. This is unnecessary as the kernel can handle the creation > > > failures of memcg kmem caches. > > > > AFAICS it will handle those by simply not accounting those objects > > right? > > > > The memcg kmem cache creation is async. The allocation has already > been decided not to be accounted on creation trigger. If memcg kmem > cache creation is failed, it will fail silently and the next > allocation will trigger the creation process again. Ohh, right I forgot that it will get retried. This would be useful to mention in the changelog as it is not straightforward from reading just the particular function. > > > Additionally CONFIG_SLAB does not > > > implement this behavior. So, to keep the behavior consistent between > > > SLAB and SLUB, removing the panic for memcg kmem cache creation > > > failures. The root kmem cache creation failure for SLAB_PANIC correctly > > > panics for both SLAB and SLUB. > > > > I do agree that panicing is really dubious especially because it opens > > doors to shut the system down from a restricted environment. So the > > patch makes sesne to me. > > > > I am wondering whether SLAB_PANIC makes sense in general though. Why is > > it any different from any other essential early allocations? We tend to > > not care about allocation failures for those on bases that the system > > must be in a broken state to fail that early already. Do you think it is > > time to remove SLAB_PANIC altogether? > > > > That would need some investigation into the history of SLAB_PANIC. I > will look into it. Well, I strongly suspect this is a relict from the past. I have hard time to believe that the system would get to a usable state if many of those caches would fail to allocate. And as Dave said in his reply it is quite silly to give this weapon to a random driver hands. Everybody just thinks his toy is the most important one... -- Michal Hocko SUSE Labs