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 C8233CD128A for ; Tue, 9 Apr 2024 21:42:44 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 359166B0085; Tue, 9 Apr 2024 17:42:44 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 308DA6B0088; Tue, 9 Apr 2024 17:42:44 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1D0F96B0089; Tue, 9 Apr 2024 17:42:44 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id F23CE6B0085 for ; Tue, 9 Apr 2024 17:42:43 -0400 (EDT) Received: from smtpin18.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id ACF181401B1 for ; Tue, 9 Apr 2024 21:42:43 +0000 (UTC) X-FDA: 81991318206.18.0699AD1 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf09.hostedemail.com (Postfix) with ESMTP id 52462140014 for ; Tue, 9 Apr 2024 21:42:41 +0000 (UTC) Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=ud318HAF; dmarc=none; spf=none (imf09.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=1712698962; a=rsa-sha256; cv=none; b=fhnBit9yZlmRJ7m0P1c6X7QUwS9WKSklr+Jz0RhWLPLFmlPzLhlRq41bDJsRrsjlAi3zQ8 cQyIp5iZQJ8xUDw+Q5wKFpC5sXHbKdbmTlV7Xb+TOLgBOny3xiRDanYkXE5e8nymLnELvQ goe/lLK0HZHNWVcJOuCI97QhOAEn3kg= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=ud318HAF; dmarc=none; spf=none (imf09.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=1712698962; 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=cAZm87PzI6fyQ1m2jU/2dvY7F4KiYWybRLHCj3v2RmA=; b=N6rSUk8Ac+9wP0/SpRcVmULUIsr52RMFCWVopLSWIbnXp2UA4xnFQOc/6l9C2W/TXncvlC 47CWF5rZw6xevaYYTeX2ILzYRTObLjPYTPt/vvbhIthGzW206vUyNB6VOuWM1nw1gBHgGO 5XHABNijm4Nrbu6xfstVJmJfSCLgIQo= 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=cAZm87PzI6fyQ1m2jU/2dvY7F4KiYWybRLHCj3v2RmA=; b=ud318HAFAMuxza1NMA5qxCWVYS Q3RQ7jjtcx3N5nPxhhPAR0r9nI5meQpupzsoLYg/sLklNXZGNvq4mJldoHmAZlB8EiPlc66C1enlq 5v9zE4iPBgno4IMn85s2hY3bY/kxn2nymlq59ieFhSg6I4plV2yvY3X40V7jN6+qA4t8AL8cjDmKV QL1wHhqVrLEbkmzXAyAszoqKaMDh+yZfRq646kXMiDKPVWpKg079mOaofT7ZiO68GJv1A7tl2Inw5 ry5F7XRa498awRyp/nbS9D2xQlZqxN9g3+IyGZhZ2iwmQQDGSZCm5jlUbR8JiU25qsEUpJwq5Ir6G 6HhHRSJw==; Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1ruJEb-00000002zqV-2c7l; Tue, 09 Apr 2024 21:42:29 +0000 Date: Tue, 9 Apr 2024 22:42:29 +0100 From: Matthew Wilcox To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, cgroups@vger.kernel.org, linux-sh@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton , Peter Xu , Ryan Roberts , Yin Fengwei , Yang Shi , Zi Yan , Jonathan Corbet , Hugh Dickins , Yoshinori Sato , Rich Felker , John Paul Adrian Glaubitz , Chris Zankel , Max Filippov , Muchun Song , Miaohe Lin , Naoya Horiguchi , Richard Chang Subject: Re: [PATCH v1 01/18] mm: allow for detecting underflows with page_mapcount() again Message-ID: References: <20240409192301.907377-1-david@redhat.com> <20240409192301.907377-2-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240409192301.907377-2-david@redhat.com> X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 52462140014 X-Stat-Signature: 13mfug8wioxju65ty7uf9nsea9tf67n1 X-HE-Tag: 1712698961-159388 X-HE-Meta: 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 qJEYB9Jz 2qFBPykW/TKvDe1JQne/wpvORZaETY5o+o/lYD3/21iPv4RSsDMA133WhY9rCrqq2gKQ4g2b6+a8OpH9+atkJkzHmch1a8HubO9eMPFDyAqWZqQqsWB9J1DtCuDhnH9obK+xjFC1kaBDhZZJvSfP4CjGueAMvPMgfELrzNezuVB7C3CDPq3ld7QicpIWINDmsTyU0U3EQqN0TjPyYwG+1nIddAA== 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: List-Subscribe: List-Unsubscribe: On Tue, Apr 09, 2024 at 09:22:44PM +0200, David Hildenbrand wrote: > Commit 53277bcf126d ("mm: support page_mapcount() on page_has_type() > pages") made it impossible to detect mapcount underflows by treating > any negative raw mapcount value as a mapcount of 0. Yes, but I don't think this is the right place to check for underflow. We should be checking for that on modification, not on read. I think it's more important for page_mapcount() to be fast than a debugging aid.