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 E84C0C52D7C for ; Mon, 12 Aug 2024 06:13:58 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 71E316B0092; Mon, 12 Aug 2024 02:13:58 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6CE516B0098; Mon, 12 Aug 2024 02:13:58 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 548506B009A; Mon, 12 Aug 2024 02:13:58 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 28E8B6B0092 for ; Mon, 12 Aug 2024 02:13:58 -0400 (EDT) Received: from smtpin26.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id CC688A5AFC for ; Mon, 12 Aug 2024 06:13:57 +0000 (UTC) X-FDA: 82442577714.26.14DD39C Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf23.hostedemail.com (Postfix) with ESMTP id 03FF0140010 for ; Mon, 12 Aug 2024 06:13:55 +0000 (UTC) Authentication-Results: imf23.hostedemail.com; dkim=none; spf=pass (imf23.hostedemail.com: domain of dev.jain@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=dev.jain@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1723443202; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=0w9HvwSoNSvofrEeOraefe39OccalxPFbhVcozePFWw=; b=rwugKRBsMMMma5/Z/1dIPNsUeinlvWx4uvTWcoVDaa28beTPxcyJYs/At9zNS8++G+YpTn 0NjmANz2E0/bq1+1pUEdumwAY3gkSB+hgrGITBfZl4PEx+O7/CnztADCUMcpsZOigjSghn +1w4J4eCkvd/95nCfm0V/qmLH4/3ZXo= ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=none; spf=pass (imf23.hostedemail.com: domain of dev.jain@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=dev.jain@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1723443202; a=rsa-sha256; cv=none; b=iAj6PvS/0MkkGMmmtvjq9/mxds8Ur7BE+Bar2fqngUCoIvX4pVBitsJesgR8ziDpsIj1ju IOu8QXKUse8zWnr0J1hPXxEveD8ND8t0NJk+Tt/nDuLxd9RiNw7wWWpqa59AWy8yqw/LyV 9Eb3RGdafj1qtTfXQ8gE0Ir/vQjwL58= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E57FFFEC; Sun, 11 Aug 2024 23:14:20 -0700 (PDT) Received: from [10.162.43.141] (e116581.arm.com [10.162.43.141]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8A38A3F73B; Sun, 11 Aug 2024 23:13:46 -0700 (PDT) Message-ID: Date: Mon, 12 Aug 2024 11:43:43 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm: Retry migration earlier upon refcount mismatch To: "Huang, Ying" Cc: akpm@linux-foundation.org, shuah@kernel.org, david@redhat.com, willy@infradead.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, cl@gentwo.org, vbabka@suse.cz, mhocko@suse.com, apopple@nvidia.com, osalvador@suse.de, baolin.wang@linux.alibaba.com, dave.hansen@linux.intel.com, will@kernel.org, baohua@kernel.org, ioworker0@gmail.com, gshan@redhat.com, mark.rutland@arm.com, kirill.shutemov@linux.intel.com, hughd@google.com, aneesh.kumar@kernel.org, yang@os.amperecomputing.com, peterx@redhat.com, broonie@kernel.org, mgorman@techsingularity.net, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org References: <20240809103129.365029-1-dev.jain@arm.com> <20240809103129.365029-2-dev.jain@arm.com> <87frrauwwv.fsf@yhuang6-desk2.ccr.corp.intel.com> Content-Language: en-US From: Dev Jain In-Reply-To: <87frrauwwv.fsf@yhuang6-desk2.ccr.corp.intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: 03FF0140010 X-Stat-Signature: gzeupzx364qjp5nenb63menuaae1its5 X-HE-Tag: 1723443235-220101 X-HE-Meta: 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 f878icPP VOPKFxj72lyK2BRAyOqg9kkDH7W/uubTFj7CII/6R5JZO2eVLsAC0oHX5aWvsLu9LsysfbPD/+AWVaMaeaD/ywr0ffD51zQQx4szRyxofR9+VJ8yI26wTSw50Lh9s1xKlGHwL8kKWEAnm82XV5PocjJgT+u/2XlAOH97MAVm2IPZ3KYLuqS5XIldLecK5E9VkMjSk0WX38KX9WvQ= 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 8/12/24 11:04, Huang, Ying wrote: > Hi, Dev, > > Dev Jain writes: > >> As already being done in __migrate_folio(), wherein we backoff if the >> folio refcount is wrong, make this check during the unmapping phase, upon >> the failure of which, the original state of the PTEs will be restored and >> the folio lock will be dropped via migrate_folio_undo_src(), any racing >> thread will make progress and migration will be retried. >> >> Signed-off-by: Dev Jain >> --- >> mm/migrate.c | 9 +++++++++ >> 1 file changed, 9 insertions(+) >> >> diff --git a/mm/migrate.c b/mm/migrate.c >> index e7296c0fb5d5..477acf996951 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -1250,6 +1250,15 @@ static int migrate_folio_unmap(new_folio_t get_new_folio, >> } >> >> if (!folio_mapped(src)) { >> + /* >> + * Someone may have changed the refcount and maybe sleeping >> + * on the folio lock. In case of refcount mismatch, bail out, >> + * let the system make progress and retry. >> + */ >> + struct address_space *mapping = folio_mapping(src); >> + >> + if (folio_ref_count(src) != folio_expected_refs(mapping, src)) >> + goto out; >> __migrate_folio_record(dst, old_page_state, anon_vma); >> return MIGRATEPAGE_UNMAP; >> } > Do you have some test results for this? For example, after applying the > patch, the migration success rate increased XX%, etc. Noting that the migration selftest is operating on a single page, before the patch, the test fails on shared-anon mappings on an average of 10 iterations of move_pages(), and after applying the patch it fails on average of 100 iterations, which makes sense because the unmapping() will get retried 3 + 7 = 10 times. > > My understanding for this issue is that the migration success rate can > increase if we undo all changes before retrying. This is the current > behavior for sync migration, but not for async migration. If so, we can > use migrate_pages_sync() for async migration too to increase success > rate? Of course, we need to change the function name and comments. > > -- > Best Regards, > Huang, Ying