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 83FC6EE49A3 for ; Tue, 22 Aug 2023 15:19:07 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A2984280041; Tue, 22 Aug 2023 11:19:06 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9D8F894001B; Tue, 22 Aug 2023 11:19:06 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8A192280041; Tue, 22 Aug 2023 11:19:06 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 77B1994001B for ; Tue, 22 Aug 2023 11:19:06 -0400 (EDT) Received: from smtpin03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 3FB6B1603CA for ; Tue, 22 Aug 2023 15:19:06 +0000 (UTC) X-FDA: 81152098692.03.45B7D28 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf17.hostedemail.com (Postfix) with ESMTP id 7669B40018 for ; Tue, 22 Aug 2023 15:19:01 +0000 (UTC) Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=OJdxrOsB; dmarc=none; spf=none (imf17.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1692717543; 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=QHXtvgp2vFB1N8oXlS+0V2S/KPy9LASs+TLCFHvkSkM=; b=7THdQmPWvxcXD0aXohOTTE3RY2eo72Tsdjs/XmUW2bBIAWYaswU7s91WN8q/Mv9QBA4f9K +IKnCZv6RvAzXEmw/tl0uquCnufXNlxvS+536KY+MwvkLseC/RtuNbaxoXfJk0uOKRjiCP 7dqpGUCEKeXNvfjPwoxvVwgj+jrzZZM= ARC-Authentication-Results: i=1; imf17.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=OJdxrOsB; dmarc=none; spf=none (imf17.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1692717543; a=rsa-sha256; cv=none; b=dndpDmicC1ykuCQ31bq1Rk4KUnm6ndoo/HmuyyaUWmSnSFyts5cF2hxK5Rjciaxtv6cn2d HdOyUXbItInDV/EGK0SBpBK/scM/eVGLAmTNf5gJ4mcxykP1wYoR1vVvQaDtTICxMNKudr weyOF0SccU3fwunAag0xdwvfj5FNxRw= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=QHXtvgp2vFB1N8oXlS+0V2S/KPy9LASs+TLCFHvkSkM=; b=OJdxrOsBxr1l3pxhaCBZm5JAUN kN4pwMf2Od0l9KwnTU4ltvBAIOJMFyRTbZoTITKp3ABLHQlIpdNkJN6mEBxpwniNqjHoefFfWKvK+ 2LXc1qfL1Trfl3+HlzW91nZiIsL2kiSG9ybwFjvKPYwqTkW+9eIfigFCRICLyvybiWUyBzGAZ7Qh5 6FYOARZeu3KLmcYWY/uoTSZc9efbYAkc3TjXFqWHbkuYmCcAWlGOUDD6zV2o2fcj/uX0cll/RNl7a CDn28g/ECXlXgW1+i8Cg8XdoVkkN6p0wmtqHrpSWqR0G5H9weFBRYJ2eNN0VcV8I/jwuet0LlZ5RN 9ni0mYYQ==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1qYT9j-00H2bq-IT; Tue, 22 Aug 2023 15:18:55 +0000 Date: Tue, 22 Aug 2023 16:18:55 +0100 From: Matthew Wilcox To: Peter Xu Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Yang Shi , Mike Kravetz , David Hildenbrand , "Kirill A . Shutemov" , Hugh Dickins , Andrew Morton Subject: Re: [PATCH] mm: Wire up tail page poisoning over ->mappings Message-ID: References: <20230815210659.430010-1-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 7669B40018 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: 6489saudxopkg3ca65au958h5q8g4rdj X-HE-Tag: 1692717541-906051 X-HE-Meta: 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 m1OwsL7b FzV7af/mPHdv7dKbVFMB9bSNI4SryxcEOx/9Ww7UnhMqNypksaAX8C5uoLmmyQsSHVL+WZZruddCOAKafARawXAtbclESExs9+gmkStLMT/CwLTzRKXr7ap4KgkwKTEyi3kgcEGJ7UMaZimzGVml8F71Jdjzoyj0RFn6oHzuFmALJzvd2R/wjeOqajinYG8e8zJD6V3OW9TQ9OPKMSE0Fz5eq84lQe+Jtsm0Pso5e1q1F4xFzt4C3z3Gu/nFLMDM2o82m 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 Mon, Aug 21, 2023 at 12:48:18PM -0400, Peter Xu wrote: > On Mon, Aug 21, 2023 at 03:29:01AM +0100, Matthew Wilcox wrote: > > On Sun, Aug 20, 2023 at 09:13:55PM -0400, Peter Xu wrote: > > > Setting tail mapping for tail 1/2 is even wrong, which part of this patch > > > fixes: > > > > > > @@ -428,7 +428,8 @@ static inline void prep_compound_tail(struct page *head, int tail_idx) > > > { > > > struct page *p = head + tail_idx; > > > > > > - p->mapping = TAIL_MAPPING; > > > + if (tail_idx > TAIL_MAPPING_REUSED_MAX) > > > + p->mapping = TAIL_MAPPING; > > > set_compound_head(p, head); > > > set_page_private(p, 0); > > > } > > > > I didn't see this. This is wrong. tail->mapping is only reused for > > large rmappable pages. It's not reused for other compound pages. > > Just to make sure we're on the same page: I think it's not only > _deferred_list (of tail page 2) that reused the mapping field (word offset > 3), but also _nr_pages_mapped (of tail page 1)? I don't see how this comment is related to the part of the email you're replying to. But yes, prep_large_rmappable overwrites ->mapping in two tail pages. > > However, I have a small patch series which enables 'allnoconfig' to > > build after renaming page->mapping to page->_mapping. Aside from fs/ > > there are *very* few places which look at page->mapping [1]. I'll post > > that patch series tomorrow. > > Assuming it's still not yet posted; I can wait and read it. I sent out a few patches. Some have made it to -next already because they're almost trivial. Nobody's commented on the difficult one. https://lore.kernel.org/linux-mm/20230821202016.2910321-1-willy@infradead.org/ > If you plan to remove the whole TAIL_MAPPING in a few days then I agree > this patch is not needed, but so far I don't know when it'll land and also > why, before that it does sound like we can still keep this patch. This patch is putting fresh paint on a condemned building. Just stop it. > Regarding the question on "why removing TAIL_MAPPING": poisoning an unused > field is always helpful to me even if not referenced with "page->mapping". > So I don't see an immediate benefit from removing the poisoning if it's > already there; OTOH not sure whether poison more unused fields will be more > helpful in general? You are wrong.