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=-2.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 D80A7C3A5A2 for ; Tue, 3 Sep 2019 20:13:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ADB9321897 for ; Tue, 3 Sep 2019 20:13:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=amazonses.com header.i=@amazonses.com header.b="Cn915Kxo" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727541AbfICUNs (ORCPT ); Tue, 3 Sep 2019 16:13:48 -0400 Received: from a9-36.smtp-out.amazonses.com ([54.240.9.36]:59984 "EHLO a9-36.smtp-out.amazonses.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725882AbfICUNr (ORCPT ); Tue, 3 Sep 2019 16:13:47 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/simple; s=6gbrjpgwjskckoa6a5zn6fwqkn67xbtw; d=amazonses.com; t=1567541625; h=Date:From:To:cc:Subject:In-Reply-To:Message-ID:References:MIME-Version:Content-Type:Feedback-ID; bh=3CTlLgcwUNm+oBDTSqVhwT6v0ROJvSsfzOlbmJ233Hs=; b=Cn915KxoRAOo3PmJZOOm/ld4evNzr6pLGhw1L27Pj4A6Fs/aZr4YyJgWGbjjuYtj jeVgNkAMHrsCuy8IfzOPqbjM31SPPbl46ewrDDjxMgWc5IdaUb6qSn4OWC/M8d9fnKh 6hQcvnAzb8uFmTKLv3L+pNjqUii1U+7KYP92y6TI= Date: Tue, 3 Sep 2019 20:13:45 +0000 From: Christopher Lameter X-X-Sender: cl@nuc-kabylake To: Matthew Wilcox cc: Michal Hocko , Vlastimil Babka , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Pekka Enberg , David Rientjes , Ming Lei , Dave Chinner , "Darrick J . Wong" , Christoph Hellwig , linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, James Bottomley , linux-btrfs@vger.kernel.org Subject: Re: [PATCH v2 2/2] mm, sl[aou]b: guarantee natural alignment for kmalloc(power-of-two) In-Reply-To: <20190901005205.GA2431@bombadil.infradead.org> Message-ID: <0100016cf8c3033d-bbcc9ba3-2d59-4654-a7c2-8ba094f8a7de-000000@email.amazonses.com> References: <20190826111627.7505-1-vbabka@suse.cz> <20190826111627.7505-3-vbabka@suse.cz> <0100016cd98bb2c1-a2af7539-706f-47ba-a68e-5f6a91f2f495-000000@email.amazonses.com> <20190828194607.GB6590@bombadil.infradead.org> <20190829073921.GA21880@dhcp22.suse.cz> <0100016ce39e6bb9-ad20e033-f3f4-4e6d-85d6-87e7d07823ae-000000@email.amazonses.com> <20190901005205.GA2431@bombadil.infradead.org> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-SES-Outgoing: 2019.09.03-54.240.9.36 Feedback-ID: 1.us-east-1.fQZZZ0Xtj2+TD7V5apTT/NrT6QKuPgzCT/IC7XYgDKI=:AmazonSES Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Sat, 31 Aug 2019, Matthew Wilcox wrote: > > The current behavior without special alignment for these caches has been > > in the wild for over a decade. And this is now coming up? > > In the wild ... and rarely enabled. When it is enabled, it may or may > not be noticed as data corruption, or tripping other debugging asserts. > Users then turn off the rare debugging option. Its enabled in all full debug session as far as I know. Fedora for example has been running this for ages to find breakage in device drivers etc etc. > > If there is an exceptional alignment requirement then that needs to be > > communicated to the allocator. A special flag or create a special > > kmem_cache or something. > > The only way I'd agree to that is if we deliberately misalign every > allocation that doesn't have this special flag set. Because right now, > breakage happens everywhere when these debug options are enabled, and > the very people who need to be helped are being hurt by the debugging. That is customarily occurring for testing by adding "slub_debug" to the kernel commandline (or adding debug kernel options) and since my information is that this is done frequently (and has been for over a decade now) I am having a hard time believing the stories of great breakage here. These drivers were not tested with debugging on before? Never ran with a debug kernel?