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 E670CEB64DD for ; Tue, 4 Jul 2023 02:26:10 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 8C912280053; Mon, 3 Jul 2023 22:26:10 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 878EA280049; Mon, 3 Jul 2023 22:26:10 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 71A92280053; Mon, 3 Jul 2023 22:26:10 -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 5F274280049 for ; Mon, 3 Jul 2023 22:26:10 -0400 (EDT) Received: from smtpin25.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id CB1974094A for ; Tue, 4 Jul 2023 02:26:09 +0000 (UTC) X-FDA: 80972339658.25.184E40F Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf09.hostedemail.com (Postfix) with ESMTP id ADEE614000F for ; Tue, 4 Jul 2023 02:26:06 +0000 (UTC) Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=OO5mHBfe; 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=1688437568; 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=M9qnnCmvZRpaI4HlH2RKu15QwZtFlOh7LcSoDYobJgg=; b=f30afOwliAWTX08R9nEXrmbrpeDPbbl0+xTifLKZ7pemCyTwlI0iM2CPxwU2kWCmFVmEOe VP1du6IhM/6QedZYAFt+eaYRleB4Zm8IzdLwcKqj4eCKcfJgNSBMucHmth86393c8YpXJx FYxMqoDbcpgCDEmO1KnRwYNkDojykYs= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=OO5mHBfe; 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=1688437568; a=rsa-sha256; cv=none; b=6JX+WBgOgo8IofVExvVniSw6vSFXDKOaQO+P0RKe0fefHZZYIOMvUsq2W79gVIM+l4d8b9 j6TJFGCkrIBbsz7yxhYHkonYo1UsRPtwVy4f9zXbdX1oTewrhNcdvhhjieeYt7gqwanD1K B8DYyvkmqI0oobFHEtUSz+T/vg71aSc= 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=M9qnnCmvZRpaI4HlH2RKu15QwZtFlOh7LcSoDYobJgg=; b=OO5mHBferSnrOrptd94FSc09o3 uiPNf8iqNogP7LM+ZigXSFyHL6eMeqpscut7HquMGj5eOJYOLkUvPPmURKLW9qxtbcVLVJvShZeWN Bdeb+QD3G0yrT1dhNeKmam7+ZZAqT8S9eZWzrqeGa6+c+S2xtatsf3FCR9haS8rBnhGfreNDS/hKM vWrryxN6MzH0VGOa2wDEv8RAtya9TtL+J4NEF0DrisUuCsUPf1/sj1PkUv1g6pMtyLrBs3e/LqSLI hmfC3tc6JmwzoIgfkYdQRQ8xBmdvsPOHBtWJcbCaZoDlgA7YQ4eKMV/8RA2DoGtYC7dA8KqtqgTP4 J5hlmG4A==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1qGVjq-008k9g-Hv; Tue, 04 Jul 2023 02:25:58 +0000 Date: Tue, 4 Jul 2023 03:25:58 +0100 From: Matthew Wilcox To: "Yin, Fengwei" Cc: Zi Yan , David Hildenbrand , linux-mm@kvack.org, Vishal Moola , Hugh Dickins , Rik van Riel Subject: Re: Folio mapcount Message-ID: References: <7DCA075B-1E43-47B1-9402-66C54513D52E@nvidia.com> <310c4d8a-e14c-742b-5c6c-018c01ed897e@intel.com> <957ea888-a96b-89cc-29e2-973bb9e36f40@intel.com> <6cec6f68-248e-63b4-5615-9e0f3f819a0a@redhat.com> <2AE20377-9111-4BCF-879E-7414808BDBA4@nvidia.com> <83534eb4-cf18-b594-98c7-1ca2b6cc3db8@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <83534eb4-cf18-b594-98c7-1ca2b6cc3db8@intel.com> X-Rspam-User: X-Stat-Signature: fnp53hadax811dm9516e5utbfxyhfxy7 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: ADEE614000F X-HE-Tag: 1688437566-446981 X-HE-Meta: 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 uuth2E7u c+2rpsPoDVpaQZOB8tWafICbEMpDV3+gS6srXRRI41LSvGTjuGzBbzgoduRMquifGy1oiDjly7Utkpsn2ls7JWG3j6M5P3iCZy+Kkc1fI4UCS4piE5lxZdqJDWPncUUZVQW2VTJSb9OQDuWRqXDvjl6OGsJnFZx9Gnlu7M+gLcjO9f2NBV5bdz4YMvAczRZwDBqlwnvbcc3+rOG8= 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, Jul 04, 2023 at 09:22:07AM +0800, Yin, Fengwei wrote: > > > On 7/3/2023 9:24 PM, Zi Yan wrote: > > On 2 Jul 2023, at 21:09, Yin, Fengwei wrote: > > > >> On 7/3/2023 3:51 AM, Zi Yan wrote: > >>>> (3) Mapcount of first (or any other) subpage (compount+subpage): for > >>>> folio_estimated_sharers(). > >>> This is another estimation. I wonder if we can use a different estimation > >>> like total_mapcount() > folio_nr_pages() instead. > >> Considering the partial folio mapping, I suppose we should use > >> total_mapcount() > folio->_nr_pages_mapped > >> as folio_estimated_sharers(). > > > > What you propose is to get a precise check instead of estimate, and you assume no PMD mapping and still require per-page mapcount. > > > > What I am proposing is to get rid of per-page mapcount, which is my goal, and use a single mapcount to do a rough estimate. > O. Sorry. I didn't notice your goal. So if the rough estimate is enough, > total_mapcount() > folio_nr_pages() works. > > Do we need to check all the cases to make sure the rough estimation is > enough for all of them? That's definitely not enough for deciding whether we need to COW a page or not. We need to be able to tell the difference between an order-4 folio with page 1 mapped in two tasks and an order-4 folio with page 0 & page 1 mapped in a single task.