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 27A0DEB64D7 for ; Sun, 18 Jun 2023 11:20:56 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 807746B0071; Sun, 18 Jun 2023 07:20:55 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 78FB26B0072; Sun, 18 Jun 2023 07:20:55 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 657A76B0075; Sun, 18 Jun 2023 07:20:55 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 5272D6B0071 for ; Sun, 18 Jun 2023 07:20:55 -0400 (EDT) Received: from smtpin13.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 183B0A0E43 for ; Sun, 18 Jun 2023 11:20:55 +0000 (UTC) X-FDA: 80915626470.13.90F6185 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf16.hostedemail.com (Postfix) with ESMTP id 04F1D180009 for ; Sun, 18 Jun 2023 11:20:51 +0000 (UTC) Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=jruA45Zx; dmarc=none; spf=none (imf16.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=1687087252; 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=PDfKEQOvoEs+ntOdENvzD9q/MXNZ4PuEsAjU3CrG4JE=; b=S/GAqDI6hNlYsft7fqDBgpjVoIh//zMGPWvfK/tepMm5UO+E4xH2eRwEezUDNablzE50wN o6F9d3GEbEDKgZYsRs3Lax1/V5PXKD+StfOiBAvpWs+7V/jvjeoCElHIyIbbzNmImFWDqP YV3+K72sugYrz1izS1Xcpo7Jikd6MkM= ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=jruA45Zx; dmarc=none; spf=none (imf16.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=1687087252; a=rsa-sha256; cv=none; b=ySGBEUJGPcVf8Kk2BacWGlQKsWhtPHr0SD/vOpjjsfFtqpNmfpYKHFuwIx3FJsJY6cGNFt GguArbH9EXIMNq1iG38C0rDSr3PoCAunSznQ8vMtd4/g7hx9ySKL5/04Th46Pl1WtH9nJb oaJkmVWEf+S/k8+DlzzgyY6QSPPHpgQ= 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=PDfKEQOvoEs+ntOdENvzD9q/MXNZ4PuEsAjU3CrG4JE=; b=jruA45ZxBcAt7/PPzuthy7X1Ms H9fn92GCaIhpvFJ30Y1I0m9aHIomePHPVFnqF1c0lM9r8BkIECxB458Jr8blBx5r2ASzlRatJS6bw 0Yyj2vvmL4MwBgoQIZiZK0fc92RfBFLIBI3OZxbrGxe7ayX+M2+9jPjxYlUH/JFGqqorScfaXXKlg svIVwhYfwMuWZwp8gO3JzJVXw/ODpbJQKNFPzWxmbR3KkSRJSw1r5N1x6JQ/OVrli12LsNapKXMfy q+sizeZ0uOdhnlmduZYIElH0HDORLlpWd6CL4msuSPYrl/l3asLOA08ne3Ll/OpyPzB9Ma1MPGgmg ywjrjPGA==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1qAqS8-00Ajoz-R3; Sun, 18 Jun 2023 11:20:16 +0000 Date: Sun, 18 Jun 2023 12:20:16 +0100 From: Matthew Wilcox To: Yosry Ahmed Cc: Andrew Morton , Yu Zhao , "Jan Alexander Steffens (heftig)" , Steven Barrett , Brian Geffon , "T.J. Alumbaugh" , Gaosheng Cui , Suren Baghdasaryan , "Liam R. Howlett" , David Hildenbrand , Jason Gunthorpe , Mathieu Desnoyers , David Howells , Hugh Dickins , Greg Thelen , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 1/5] mm/mlock: rework mlock_count to use _mapcount for order-0 folios Message-ID: References: <20230618065744.1363948-1-yosryahmed@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230618065744.1363948-1-yosryahmed@google.com> X-Rspamd-Queue-Id: 04F1D180009 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: efgwqayitjog91uqus7uininq78faxgm X-HE-Tag: 1687087251-335273 X-HE-Meta: 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 dIPmT2Mn mXE150udJvLCOYxPLAZBb8XzjoVprAxmxZvezVDA5JmcxmrQl4FLK0iQh8+L+UfljA51L/D4ZWVFrUA0I0LPW9cvauYXapTvJ+vueIvqtgiFQrAOXI474FCyuuNzh3INEfL9WcRhDPsBde1MRFOOrbxNTsfR0ukonGUl5UG2EF7OUaIOKcSXzq9p/jg== 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 Sun, Jun 18, 2023 at 06:57:44AM +0000, Yosry Ahmed wrote: > @@ -337,6 +318,7 @@ struct folio { > atomic_t _entire_mapcount; > atomic_t _nr_pages_mapped; > atomic_t _pincount; > + atomic_t _mlock_count; > #ifdef CONFIG_64BIT > unsigned int _folio_nr_pages; > #endif You can't quite do this. On 32-bt systems (I know, I know ...), we have: offset page 0 page 1 0 flags flags 4 lru head 8 lru dtor+order 12 mapping entire_mapcount 16 index nr_pages_napped 20 private pincount 24 mapcount 28 refcount so it actually ends up overlapping page->mapcount on the second page, which is of course used for counting the number of PTEs which map that specific page. I don't have a scenario where this would matter, but we are quite careful to only allocate order-2+ large folios, so I'd suggest putting it in page 2 instead of page 1. I should probably add a comment to struct folio warning of this dragon. I thought the #ifdef CONFIG_64BIT would be enough to warn unwary passers-by of its presence, but a more explicit sign must be in order.