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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id bz26-20020a05622a1e9a00b0039c7b9522ecsm1790130qtb.35.2022.10.25.08.45.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Oct 2022 08:45:54 -0700 (PDT) Date: Tue, 25 Oct 2022 08:45:45 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Vlastimil Babka cc: Hugh Dickins , Matthew Wilcox , Hyeonggon Yoo <42.hyeyoo@gmail.com>, David Laight , Joel Fernandes , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, rcu@vger.kernel.org, David Laight , Kees Cook Subject: Re: amusing SLUB compaction bug when CC_OPTIMIZE_FOR_SIZE In-Reply-To: <32fe01dc-dda1-2154-af8e-7e9f64d6f811@suse.cz> Message-ID: <8773771c-5370-f9f9-8f5c-67385c3cd25f@google.com> References: <35502bdd-1a78-dea1-6ac3-6ff1bcc073fa@suse.cz> <7dddca4c-bc36-2cf0-de1c-a770bef9e1b7@suse.cz> <904cc831-eb16-b1e5-10e5-9e7a171ef83@google.com> <32fe01dc-dda1-2154-af8e-7e9f64d6f811@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1666712756; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=ImmYV/dFFzxheZ2arZHQD1BqoZetMRNq1pHAiijomwY=; b=AfjXTujyDsooGsLIXfQT1Uddh6zCIKoF+c7zARKTrlJXhoQdXtM+JCfO7MDdTSJzCRYK63 u6rfqksGMSqGoXlduaQ2yquA9m0b5bHMihl5gvwGYB0vRgsjU3sY45H5TMEY0+iMfALmUr GynsCO9MilyF9Dxv4xa7X87uYPtjAGc= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=QMp+lR8v; spf=pass (imf03.hostedemail.com: domain of hughd@google.com designates 209.85.222.176 as permitted sender) smtp.mailfrom=hughd@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1666712756; a=rsa-sha256; cv=none; b=KQgYpm5RzRPTXKyfK23YZTy+fZey/g7BEjHcJorgTOz5htX8SmjsOE68ocvvd7Jd3Gd+sh x+jRb1TH3L6KOsukCRvRcAUH6q5rtXkOL1UOInbmG1kbyWevsu/gxbiut3HPz65QLP7Kj8 Myo4RfIBK+wOTqoSsP7DpupHV3zdyWU= Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=QMp+lR8v; spf=pass (imf03.hostedemail.com: domain of hughd@google.com designates 209.85.222.176 as permitted sender) smtp.mailfrom=hughd@google.com; dmarc=pass (policy=reject) header.from=google.com X-Stat-Signature: gsdtxc58x31wf51ochkoi6tqqja4xot8 X-Rspamd-Queue-Id: 9CA2420040 X-Rspamd-Server: rspam07 X-Rspam-User: X-HE-Tag: 1666712756-933407 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, 25 Oct 2022, Vlastimil Babka wrote: > On 10/25/22 06:19, Hugh Dickins wrote: > > On Mon, 24 Oct 2022, Vlastimil Babka wrote: > > >> > >> [1] https://lore.kernel.org/all/aec59f53-0e53-1736-5932-25407125d4d4@suse.cz/ > > > > Ignore me, don't let me distract if you're happy with Matthew's patch > > (I know little of PageMovable, and I haven't tried to understand it); > > but it did look to me more like 6.2 material, > > Yes, it is targetted towards 6.2 now. That's good. > > > and I was surprised that > > you dropped the simple align(4) approach for 6.1. > > > > Because of Hyeonggon's rcu_leak_callback() observation? That was a > > good catch, but turned out to be irrelevant, because it was only for > > an RCU debugging option, which would never be set up on a struct page > > (well, maybe it would in a dynamically-allocated-struct-page future). > > It was mainly due to David's observation: > > https://lore.kernel.org/all/c1c8920a56014a179dbb82d483f2ad28@AcuMS.aculab.com/ > > I did also conclude that align(4) indeed overrides anything set via > CONFIG_FUNCTION_ALIGNMENT (and passed by -falign-functions) in a way that a > globally configured larger alignment can be made smaller by this macro, and > it was all too risky and last minute to me, while Joel's series wasn't > targetted to 6.1 anyway so there was no urgency. Oh, I had thought it was heading for 6.1. Yes, you have good reason to drop the alignment trick there - thanks for verifying David's point. I hadn't seen followup, and assumed that the earlier i915 example gave assurance that alignment was usable (but maybe that's part of why the i915 folks stopped doing it that way). Thanks, Hugh > > And yeah it looks like a gcc bug to me. > > > Hugh