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 00394C25B08 for ; Wed, 17 Aug 2022 16:09:08 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 8B05F8D0001; Wed, 17 Aug 2022 12:09:08 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 85FE66B007D; Wed, 17 Aug 2022 12:09:08 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 727748D0001; Wed, 17 Aug 2022 12:09:08 -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 618CC6B007B for ; Wed, 17 Aug 2022 12:09:08 -0400 (EDT) Received: from smtpin29.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 429A0A1634 for ; Wed, 17 Aug 2022 16:09:08 +0000 (UTC) X-FDA: 79809568776.29.C1862C8 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by imf05.hostedemail.com (Postfix) with ESMTP id D540C100067 for ; Wed, 17 Aug 2022 16:09:07 +0000 (UTC) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 6F2ACB81E2F; Wed, 17 Aug 2022 16:09:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9EED3C433B5; Wed, 17 Aug 2022 16:09:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1660752545; bh=Fr5BK5q+jt50WHSkwoTNXLWBroAySOyM0j0vhn4tsHo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=RXmjnC+w3WIxoJ6B2CV0dvuG4o3oJa1N1qLw+oRW6EdETz/GNY2KBVIKS+8PvK96O BXB1m6Y/5Xi6grE2mnUZlnMTNeZH8ik/TUa6JrQgFg8rdFn0Q8eLQgwatUH1uWrqDK T3zgXMGmVF7fXXi4NzAwQ98Jg43WZ0CFKvkXIYQwLmqHyQv96p0zpvDrPV5oI9UWeE V60KIK3gm1iaTEJgPods84LibmBf4AbNI1rABrL1/Y0LcqC+c8B1LZNFv5mIIdDoVw oAI6pcuq0UnC8m2xFQd2uqTLxyKaEueVGXCjYEOrN7uu5yN/wL8TmmVOOwJbLNhHX1 lDFCPnuvmXkvw== From: SeongJae Park To: Baolin Wang Cc: sj@kernel.org, akpm@linux-foundation.org, damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/damon: Validate if the pmd entry is present before accessing Date: Wed, 17 Aug 2022 16:09:02 +0000 Message-Id: <20220817160902.98613-1-sj@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <2838b6737bc259cf575ff11fd1c4b7fdb340fa73.1660717122.git.baolin.wang@linux.alibaba.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660752548; a=rsa-sha256; cv=none; b=rCNbkxbiqb5WMqGzcyTrGQkZqLB3/dDMMZkdSTg1g2b8r5lI0/fQE0eRq9C8UjGg2+8kHr Poel7Rr53k7XZQIjjoVm3aVj01b9/vLxrKDuGwsgKECBy9aMyjHc7RHeUdcicu2KPP+Sji vaiYgangrP9yXKO/RUZi6Mf19fggzYk= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=RXmjnC+w; spf=pass (imf05.hostedemail.com: domain of sj@kernel.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=sj@kernel.org; dmarc=pass (policy=none) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660752548; 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-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=QP2uVE9aVOSf+m5OkloLNvwLJxzeSYT31/pr0iS9trQ=; b=aBipUuEijLrqDnxQXa7ojGvzLRZ+MBtdUsobyfTuolFujtSpgUat9oNzKA68bXIP+s6XAK HO7RIISI3AzOI5ZLUra/ienHrCcmPs/T99TUknXxx3zTEsRwGH6ov8Ov1MQg/UP2AdUp6S AAu01TDYzNx/K2WP/m7XfFC+SdFg58g= X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: D540C100067 X-Rspam-User: Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=RXmjnC+w; spf=pass (imf05.hostedemail.com: domain of sj@kernel.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=sj@kernel.org; dmarc=pass (policy=none) header.from=kernel.org X-Stat-Signature: 83dj7jjx4ysmo9jjk66wr4jnk5pccm6t X-HE-Tag: 1660752547-398954 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: Hi Baolin, Thank you always for your great patch! On Wed, 17 Aug 2022 14:21:12 +0800 Baolin Wang wrote: > The pmd_huge() is used to validate if the pmd entry is mapped by a huge > page, also including the case of non-present (migration or hwpoisoned) > pmd entry on arm64 or x86 architectures. Thus we should validate if it > is present before making the pmd entry old or getting young state, > otherwise we can not get the correct corresponding page. Maybe I'm missing something, but... I'm unsure if the page is present or not really matters from the perspective of access checking. In the case, DAMON could simply report the page has accessed once for the first check after the page being non-present if it really accessed before, and then report the page as not accessed, which is true. Please let me know if I'm missing something. Thanks, SJ > > Signed-off-by: Baolin Wang > --- > mm/damon/vaddr.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c > index 3c7b9d6..1d16c6c 100644 > --- a/mm/damon/vaddr.c > +++ b/mm/damon/vaddr.c > @@ -304,6 +304,11 @@ static int damon_mkold_pmd_entry(pmd_t *pmd, unsigned long addr, > > if (pmd_huge(*pmd)) { > ptl = pmd_lock(walk->mm, pmd); > + if (!pmd_present(*pmd)) { > + spin_unlock(ptl); > + return 0; > + } > + > if (pmd_huge(*pmd)) { > damon_pmdp_mkold(pmd, walk->mm, addr); > spin_unlock(ptl); > @@ -431,6 +436,11 @@ static int damon_young_pmd_entry(pmd_t *pmd, unsigned long addr, > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > if (pmd_huge(*pmd)) { > ptl = pmd_lock(walk->mm, pmd); > + if (!pmd_present(*pmd)) { > + spin_unlock(ptl); > + return 0; > + } > + > if (!pmd_huge(*pmd)) { > spin_unlock(ptl); > goto regular_page; > -- > 1.8.3.1