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 E6E1BC001B0 for ; Mon, 14 Aug 2023 19:09:04 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 2E5D0900003; Mon, 14 Aug 2023 15:09:04 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 26D6D8E0003; Mon, 14 Aug 2023 15:09:04 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 10EB6900003; Mon, 14 Aug 2023 15:09:04 -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 F14368E0003 for ; Mon, 14 Aug 2023 15:09:03 -0400 (EDT) Received: from smtpin20.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id C3C7D1C9ADE for ; Mon, 14 Aug 2023 19:09:03 +0000 (UTC) X-FDA: 81123647766.20.FC540F8 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf01.hostedemail.com (Postfix) with ESMTP id 1650E40011 for ; Mon, 14 Aug 2023 19:09:01 +0000 (UTC) Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=eNqrWt3I; dmarc=none; spf=none (imf01.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=1692040142; 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=oVU9t1+lizTyVE1f/fKD/tkH+rpOHpGVs/bdM6v21qY=; b=lH6As17l2GL4B+1n6EY3Hj08lOj6Sv0j1XS6ds2Pp7n9B/zH6+gtKSACTbCdOyJwqM0U0Y 6PEAaSbOBnh2MDDiVkym+/8Z1w5FMin1TWarxZDG+UGL7WVnELun3jL3FGPhP9E1ec6HWX 8e33cYJNelhChZRcHViPhsTogOOXjKg= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=eNqrWt3I; dmarc=none; spf=none (imf01.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=1692040142; a=rsa-sha256; cv=none; b=n9wb9Zm7CybvC7f4eTAe/rCEKw8wzleJgc+p8/qMgkmxzp2wSKKD3+2n9UUOojdXU58kGl c4YEMo5DnVeO/bpXzHP5bTUkCqlf4BJ09P+VIGsOC8tL6kwrfkJoUi1BksW0sI6SRTzVah tj1zlWxo4nfORjVRKqp5WIH9GNxu6aQ= 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=oVU9t1+lizTyVE1f/fKD/tkH+rpOHpGVs/bdM6v21qY=; b=eNqrWt3I4iP49TuR4/Nn4hjgVp 7NR4Ch5oBDMbDI447MGCuZxWLKBTJdtA3gvJ+3HqOitb2wAkh592q2t+quvqqev2NQX6eBh4hsHJt 2Xx1rDoE5j+amaiUfE8Ebzw8noA988kE6i8TKdBobtzZJT0LNYIzuknX1NQhjTgazSka8ZLpmqbUO ofvOjCh9PZ3MTaOocaWrhSiyn7d4h9N8A3vE+GUGLP4VsRmNAFxMUe6yvHruXLVtjgpy2wfehGoH4 oU7D81fbrTcviazkqTDl0wYlvbw1CJgAYtp7YvFwb/kuKK2amKFMih5L1hJro4GTtZ1gYWpAVpYKh iPN3hwJg==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1qVcvx-003iZo-Bz; Mon, 14 Aug 2023 19:08:57 +0000 Date: Mon, 14 Aug 2023 20:08:57 +0100 From: Matthew Wilcox To: Peter Xu Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mike Kravetz , David Hildenbrand , Andrew Morton , Yu Zhao , Ryan Roberts , Yang Shi , Hugh Dickins , "Kirill A . Shutemov" Subject: Re: [PATCH RFC v2 1/3] mm: Add TAIL_MAPPING_REUSED_MAX Message-ID: References: <20230814184411.330496-1-peterx@redhat.com> <20230814184411.330496-2-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230814184411.330496-2-peterx@redhat.com> X-Rspamd-Queue-Id: 1650E40011 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: ishusa96n6ygqnyx5dwp919tzy1xc9hi X-HE-Tag: 1692040141-672280 X-HE-Meta: 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 yMH7hQOq sw+bhECTbR9wQ4jvvGtAnUMNr5DivzEWC4RObdedJN5Ye6bxxNkOV1IDZ/Lyn5LYS7kEquAWL7CNSMU8aOXvR8uVS7tcBG0qP46Rx4rfioTnmhksiK86j9of4VH0OCDB/vEYNhYNg4F9N+j21UBRMjnPJTmY1zuXWFMAoFJKQxBayc+L5A85xH4E20Q== 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 14, 2023 at 02:44:09PM -0400, Peter Xu wrote: > +/* > + * This macro defines the maximum tail pages (of a folio) that can have the > + * page->mapping field reused (offset 12 for 32bits, or 24 for 64bits). No, don't say how many bytes into the structure something is. It'll only get out of date. If somebody needs to know, use pahole. > + * When the tail page's mapping field reused, it'll be exempted from > + * ->mapping poisoning and checks. Also see the macro TAIL_MAPPING. > + */ > +#define TAIL_MAPPING_REUSED_MAX (2) More importantly, I think this is over-parametrisation. If you start to use extra fields in struct folio, just change the code in page_alloc.c directly.