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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id B1800C433FE for ; Fri, 30 Sep 2022 07:39:51 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D053D8D0002; Fri, 30 Sep 2022 03:39:50 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C8DB28D0001; Fri, 30 Sep 2022 03:39:50 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B55C18D0002; Fri, 30 Sep 2022 03:39:50 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id A74308D0001 for ; Fri, 30 Sep 2022 03:39:50 -0400 (EDT) Received: from smtpin15.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 7ACE0A151C for ; Fri, 30 Sep 2022 07:39:50 +0000 (UTC) X-FDA: 79967952540.15.D8C5D66 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by imf09.hostedemail.com (Postfix) with ESMTP id C01DA140007 for ; Fri, 30 Sep 2022 07:39:49 +0000 (UTC) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 164D61F460; Fri, 30 Sep 2022 07:39:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1664523588; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VdrA4yqPrHCz2RiBS5dNiY3uDpMq1COfxzCZsf8wbPg=; b=HdCtZHuV/5hiApVAYBlsW1Nine9pPwtWO53QVbErTbVUZ0MloFIjMqI993kO3L4/MjDOW6 baEVztJT+KMnPopWOKFqfZUbHMj+yzKroHCknMQIuTcUbaD91sFArQcFtL8BKLzlRYv1sO +vF3/w8mUfOGulf9c02Xg/Xn1m8UOcE= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1664523588; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VdrA4yqPrHCz2RiBS5dNiY3uDpMq1COfxzCZsf8wbPg=; b=uZ1/CXvEP98D9+g9G9pqhGIFXMnka+k2mluJqDz6gIKMcKXWcoKy24RsVvhQq4cpe8lL3O 5wZEuYGpKr5a+jDQ== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id E7BF313677; Fri, 30 Sep 2022 07:39:47 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id HIpKN0OdNmP4LQAAMHmgww (envelope-from ); Fri, 30 Sep 2022 07:39:47 +0000 Message-ID: Date: Fri, 30 Sep 2022 09:39:47 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.3.0 Subject: Re: amusing SLUB compaction bug when CC_OPTIMIZE_FOR_SIZE To: Hugh Dickins Cc: David Laight , Joel Fernandes , Hyeonggon Yoo <42.hyeyoo@gmail.com>, Matthew Wilcox , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <35502bdd-1a78-dea1-6ac3-6ff1bcc073fa@suse.cz> Content-Language: en-US From: Vlastimil Babka In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1664523590; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=VdrA4yqPrHCz2RiBS5dNiY3uDpMq1COfxzCZsf8wbPg=; b=nLkdK8SG5LTnZidju8FCEaetaq0hQ0P2CecjqaW4TkQcmQClZLfbyBXpTNR4ynHYDzhxgC 8J/1Thypudb4U7+Xp/gqqF/RV4yi03rfPCr6sZADEOjGqY9MYi85Pahmikllqwdigt+UNW griksggu8N85h3JNrHPONz39Ril8jm0= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=HdCtZHuV; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b="uZ1/CXvE"; spf=pass (imf09.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.29 as permitted sender) smtp.mailfrom=vbabka@suse.cz; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1664523590; a=rsa-sha256; cv=none; b=x/kWR1q+soU+IKfhk0KBxhvbu/otSZQ4lYb+sH2+K+Kegmbo4V8ckKvte/XZSAmbKaNQqw sJv94q8Q7hXoPZYjTipnpME6naVjURobUlbg8n3y686HDB95wuswV+qN6tKJo5c0ZzcB2b /DFyGvoO1nQnQcS0IXxSjxBqSBJ/8ow= X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: C01DA140007 Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=HdCtZHuV; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b="uZ1/CXvE"; spf=pass (imf09.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.29 as permitted sender) smtp.mailfrom=vbabka@suse.cz; dmarc=none X-Stat-Signature: zfjoat75jniaiow7qg4x5uk3qxnhyso8 X-HE-Tag: 1664523589-696733 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 9/29/22 23:54, Hugh Dickins wrote: > On Thu, 29 Sep 2022, Vlastimil Babka wrote: >> On 9/28/22 19:50, Hugh Dickins wrote: >> > On Wed, 28 Sep 2022, Vlastimil Babka wrote: >> >> On 9/28/22 15:48, Joel Fernandes wrote: >> >> > On Wed, Sep 28, 2022 at 02:49:02PM +0900, Hyeonggon Yoo wrote: >> >> >> On Tue, Sep 27, 2022 at 10:16:35PM -0700, Hugh Dickins wrote: >> >> >>> It's a bug in linux-next, but taking me too long to identify which >> >> >>> commit is "to blame", so let me throw it over to you without more >> >> >>> delay: I think __PageMovable() now needs to check !PageSlab(). >> >> >> >> When I tried that, the result wasn't really nice: >> >> >> >> https://lore.kernel.org/all/aec59f53-0e53-1736-5932-25407125d4d4@suse.cz/ >> >> >> >> And what if there's another conflicting page "type" later. Or the debugging >> >> variant of rcu_head in struct page itself. The __PageMovable() is just too >> >> fragile. >> > >> > I don't disagree (and don't really know all the things you're thinking >> > of in there). But if it's important to rescue this feature for 6.1, a >> > different approach may be the very simple patch below (I met a similar >> > issue with OPTIMIZE_FOR_SIZE in i915 a year ago, and just remembered). >> > >> > But you be the judge of it: (a) I do not know whether rcu_free_slab >> > is the only risky address ever stuffed into that field; and (b) I'm >> > clueless when it comes to those architectures (powerpc etc) where the >> > the address of a function is something different from the address of >> > the function (have I conveyed my cluelessness adequately?). >> >> Thanks a lot Hugh! That's a sufficiently small fix (compared to the other >> options) that I'm probably give it one last try. > > I suddenly worried that you might be waiting on me for a Signed-off-by, > which I couldn't give until I researched my reservations (a) and (b): > but I'm pleased to see from your kernel.org tree that you've gone ahead > and folded it in - thanks. Yeah could have been more explicit about that, sorry. But made the whole thing a very last merge so I can still drop it before the pull request. > Regarding (a): great, you've found it too, mm/slab.c's kmem_rcu_free() > looks like it needs the same __aligned(4) as mm/slub.c's rcu_free_slabi(). Right. > Regarding (b): I booted the PowerMac G5 to take a look, and dredged up > the relevant phrase "function descriptor" from depths of my memory: I > was right to consider that case, but it's not a worry - the first field > of a function descriptor structure (on all the architectures I found it) > is the function address, so the function descriptor address would be > aligned 4 or 8 anyway. Thanks. I admit I wasn't that thorough, just consulted somebody internally :) > Regarding "conflicting" alignment requests: yes, I agree with you, > it would have to be a toolchain bug if when asked to align 2 and to > align 4, it chose not to align 4. Yeah. But I still would be less worried if another __aligned(X) function existed in the tree already. Found only data. I assume the i915 thing wasn't fixed like this in the tree? So if there are buggy toolchains or anything, it will be us to discover them. So I think we still should defuse the __PageMovable() mine somehow. > So, no worries at my end now. > Hugh