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 122D2C25B77 for ; Tue, 21 May 2024 00:40:36 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 83D4E6B008C; Mon, 20 May 2024 20:40:35 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7EC796B0092; Mon, 20 May 2024 20:40:35 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6B4646B0093; Mon, 20 May 2024 20:40:35 -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 4CD986B008C for ; Mon, 20 May 2024 20:40:35 -0400 (EDT) Received: from smtpin05.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id F2136140FEB for ; Tue, 21 May 2024 00:40:34 +0000 (UTC) X-FDA: 82140547188.05.5B3398F Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf18.hostedemail.com (Postfix) with ESMTP id 9E4AA1C0006 for ; Tue, 21 May 2024 00:40:32 +0000 (UTC) Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=R+Lj7Z7v; spf=none (imf18.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1716252033; 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=fhJpPLfuGesh5xjpS2ooud1QHAhQN17zzkTpX05wogo=; b=6KlrlsB7+Gjj5BNHtKeW64SBBeJELznlcVob/8kdavshdKt9U2BjkbQthBp+DAei+HRAN2 bq3O212WPZ/FNEKPOHEGy9avaVZ13MRRGNR4zxxaRobkkfRMwEba0GjS9Fmvm6JzZyfzL7 7623pelOeQXHCKf4ZvTrY2DlvEQBJOU= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1716252033; a=rsa-sha256; cv=none; b=6KURe8eTQOPdNcFCT8Sp6PSM85JCuoGa/hdviY9lsvFGG9nFde6qiYzPOMlN6kYWUN5CAB DCczKMZYknilpeRzn0IBDvH4dkdlSs5w6qjKsOb5duKpvZCsYAqS39GFp0xu8fKQh5ye+f TiqMjEP08bg8R7u+i10mcyLy3/ElJzw= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=R+Lj7Z7v; spf=none (imf18.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none 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=fhJpPLfuGesh5xjpS2ooud1QHAhQN17zzkTpX05wogo=; b=R+Lj7Z7v6/FN80b12xRt8G1B6L grttWoFFRn8nll+Zj0fbeGOQ4UpJxel0aNToiDuunEGDZG7KGSC8MdkyBiTmeB648GIBRUHaatq9H Fq1S7lbcKQL4q2zOI+ZwAJ0C8WjfVw0XrH9QTukhaHlPc5Q3Kiep8xKakIzbj0d7g2MFXC/K0vvno 2VRQl7bYA9h4mr40KSKSFixezJ9Rbiu1Pew8y+yTqHLbdlZvwxH1mZOPP3nU/gTW6dia/ASyV9ru2 JgVF8tDPZhETsFexqFumDANwDt6zPYpx1/mj/gH1IjWiR/Y7xoRLS5D9gRPjglYtOxhzeM0gPv2qG 9wmt/kGQ==; Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1s9DYI-0000000GXPM-3aa3; Tue, 21 May 2024 00:40:26 +0000 Date: Tue, 21 May 2024 01:40:26 +0100 From: Matthew Wilcox To: Sidhartha Kumar Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, vishal.moola@oracle.com, muchun.song@linux.dev, peterx@redhat.com, osalvador@suse.de Subject: Re: [PATCH] mm/hugetlb: remove {Set,Clear}Hpage macros Message-ID: References: <20240520224407.110062-1-sidhartha.kumar@oracle.com> <26e49614-ddb5-4d4c-97c1-a3a8c06d5bb5@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <26e49614-ddb5-4d4c-97c1-a3a8c06d5bb5@oracle.com> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 9E4AA1C0006 X-Rspam-User: X-Stat-Signature: 8mzd4zrp157nnrwxn8awor6anejwmkni X-HE-Tag: 1716252032-271332 X-HE-Meta: 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 3gpAWVpG TOmQ6RRVXO1Ca8CTurqf2OlEmUNCN1oa5Wyjez1T+uqVudn/AP401bUo1NBvd0nqIqMBqi2/SUbaqRS2057OcqySf6i6HT2uH7ug4ssU98372kbSpfugNpIVdvl1wU1K2YzF5XZpgpo4NY+tGzTRW/hmbVD2n5tlFvA1oyXYKx+2XlHP5aUwIXbVAFQPwEVfyM3qLgb0eMTdvnlnuXFgEWfZFlHy3UpVhvSK4PZZ8GmDcoYYW29CFViaIte/mKAFsHcSQ 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 Mon, May 20, 2024 at 04:44:53PM -0700, Sidhartha Kumar wrote: > On 5/20/24 4:30 PM, Matthew Wilcox wrote: > > On Mon, May 20, 2024 at 03:44:07PM -0700, Sidhartha Kumar wrote: > > > All users have been converted to use the folio version of these macros, > > > we can safely remove the page based interface. > > > > Yay! > > > > Reviewed-by: Matthew Wilcox (Oracle) > > There is only one remaining user of page-based Test version of these macros. > > in mm/memory-hotplug.c: > > if (!PageHuge(page)) > continue; > head = compound_head(page); > /* > * This test is racy as we hold no reference or lock. The > * hugetlb page could have been free'ed and head is no longer > * a hugetlb page before the following check. In such unlikely > * cases false positives and negatives are possible. Calling > * code must deal with these scenarios. > */ > if (HPageMigratable(head)) > goto found; > skip = compound_nr(head) - (pfn - page_to_pfn(head)); > > > I've previously sent a patch to convert this to folios[1] but got feedback > that it was unsafe. But I'm not sure why replacing compound_head() with > page_folio() and using folio_test_hugetlb_migratable(folio) rather than > HPageMigratable(head) changes the existing behavior. With no reference or > lock, can't the head pointer also be moved and no longer be a part of page > like the comment states. So would the folio conversion just be maintaining > this level of existing un-safety that the calling code should handle > anyways? To be fair, that wasn't the last thing I said about that ... https://lore.kernel.org/lkml/Y89DK23hYiLtgGNk@casper.infradead.org/ and looked like David agreed that this was a case where false postive/negative was fine; we were just looking to be right most of the time.