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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 4BE80C10F03 for ; Thu, 28 Mar 2019 10:30:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1B515206B6 for ; Thu, 28 Mar 2019 10:30:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726840AbfC1Ka2 (ORCPT ); Thu, 28 Mar 2019 06:30:28 -0400 Received: from foss.arm.com ([217.140.101.70]:42120 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725987AbfC1Ka2 (ORCPT ); Thu, 28 Mar 2019 06:30:28 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 16F7F15AB; Thu, 28 Mar 2019 03:30:26 -0700 (PDT) Received: from arrakis.emea.arm.com (arrakis.cambridge.arm.com [10.1.196.78]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 03B863F59C; Thu, 28 Mar 2019 03:30:23 -0700 (PDT) Date: Thu, 28 Mar 2019 10:30:21 +0000 From: Catalin Marinas To: Pekka Enberg Cc: Qian Cai , akpm@linux-foundation.org, cl@linux.com, mhocko@kernel.org, willy@infradead.org, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4] kmemleak: survive in a low-memory situation Message-ID: <20190328103020.GA10283@arrakis.emea.arm.com> References: <20190327005948.24263-1-cai@lca.pw> 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, Mar 28, 2019 at 08:05:31AM +0200, Pekka Enberg wrote: > On 27/03/2019 2.59, Qian Cai wrote: > > Unless there is a brave soul to reimplement the kmemleak to embed it's > > metadata into the tracked memory itself in a foreseeable future, this > > provides a good balance between enabling kmemleak in a low-memory > > situation and not introducing too much hackiness into the existing > > code for now. > > Unfortunately I am not that brave soul, but I'm wondering what the > complication here is? It shouldn't be too hard to teach calculate_sizes() in > SLUB about a new SLAB_KMEMLEAK flag that reserves spaces for the metadata. I don't think it's the calculate_sizes() that's the hard part. The way kmemleak is designed assumes that the metadata has a longer lifespan than the slab object it is tracking (and refcounted via get_object/put_object()). We'd have to replace some of the rcu_read_(un)lock() regions with a full kmemleak_lock together with a few more tweaks to allow the release of kmemleak_lock during memory scanning (which can take minutes; so it needs to be safe w.r.t. metadata freeing, currently relying on a deferred RCU freeing). Anyway, I think it is possible, just not straight forward. -- Catalin