From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id E4C31481AB; Mon, 12 Aug 2024 06:13:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723443238; cv=none; b=hSK3T+kEEGvrMPvPmWg7xv0r3MSnXNemI3LYL8unJIvf10Gd/njCydodLwGkvTcMmDcxEg3cHWwQfgq0fDPl81GkF988EVzNjZlnzDLluZ0ZAO+1CF/BQKibL1SNXQ6J4J40xFaGnMrjfmSSeSounYsewju3b/GxG+2PWC5eNAQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723443238; c=relaxed/simple; bh=kLJVQa7iClqMXsovsQziDJ7AcL+pKkrGJENBBh6aUdY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=aJgMQA26UlODHdUksajvL4SuFx1Ac5S/NtGP71kCJDFsDcrN00sqC7jSOohlpv63GRsMxxQ1iGT8uE/KA+udUgJSj8b6gsNg3NXUKj1SwrnzhXVwx0oRD0Qi+EUEXaLAGyokDwU46RjLyRc+fZq2McRdoCCDWP4lRIM306oAVe8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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