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Mon, 19 Oct 2020 10:29:55 +0000 Received: from BY5PR11MB4241.namprd11.prod.outlook.com ([fe80::adbd:559a:4a78:f09b]) by BY5PR11MB4241.namprd11.prod.outlook.com ([fe80::adbd:559a:4a78:f09b%6]) with mapi id 15.20.3477.028; Mon, 19 Oct 2020 10:29:54 +0000 Subject: Re: [PATCH v2] mm/compaction: Rename 'start_pfn' to 'iteration_start_pfn' in compact_zone() To: Vlastimil Babka , akpm@linux-foundation.org, david@redhat.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20201019083632.25417-1-yanfei.xu@windriver.com> <57730b8a-f5d7-d6c7-3961-3fa95701aba5@suse.cz> From: "Xu, Yanfei" Message-ID: <4aa294a0-c256-7e89-55af-6a7c790eec4d@windriver.com> Date: Mon, 19 Oct 2020 18:29:49 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 In-Reply-To: <57730b8a-f5d7-d6c7-3961-3fa95701aba5@suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [60.247.85.82] X-ClientProxiedBy: BYAPR07CA0040.namprd07.prod.outlook.com (2603:10b6:a03:60::17) To BY5PR11MB4241.namprd11.prod.outlook.com (2603:10b6:a03:1ca::13) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [128.224.162.160] (60.247.85.82) by BYAPR07CA0040.namprd07.prod.outlook.com (2603:10b6:a03:60::17) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3477.20 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-OriginatorOrg: windriver.com X-MS-Exchange-CrossTenant-Network-Message-Id: 9e658b36-365a-4bcd-f64b-08d87419eb49 X-MS-Exchange-CrossTenant-AuthSource: BY5PR11MB4241.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 Oct 2020 10:29:54.7030 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ddb2873-a1ad-4a18-ae4e-4644631433be X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: imzlBt4dsKGPp54jED2Osynfn2UFoUeiZ4AbwXJKhVpCKdnTKydez8HXcuD4ZjFnzgEQRbXXzze6/eQ6ejFqZg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR11MB3767 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/19/20 5:40 PM, Vlastimil Babka wrote: > On 10/19/20 10:36 AM, yanfei.xu@windriver.com wrote: >> From: Yanfei Xu >> >> There are two 'start_pfn' declared in compact_zone() which have >> different meaning. Rename the second one to 'iteration_start_pfn' >> to prevent trace_mm_compaction_end() from tracing an undesirable >> value. > > "to prevent confusion.", because trace_mm_compaction_end() has the > correct value even before the patch - the second start_pfn is out > of scope at that point. > > Thanks > In the while-statement, the second start_pfn is always be reassigned the value of cc->migrate_pfn in every loop, also the cc->migrate_pfn might be changed in the loop. Does trace_mm_compaction_end() really want to trace the new assinged start_pfn? Without the patch： 566e54e11（mm, compaction: remove last_migrated_pfn from compact_control）, there is only one start_pfn which has a fixed value. The trace_mm_compaction_end() trace it too. Thus, I think the tracepoint might get an undesireble value.:) Thanks, Yanfei >> BTW, remove an useless semicolon. >> >> Acked-by: David Hildenbrand >> Acked-by: Vlastimil Babka >> Signed-off-by: Yanfei Xu >> --- >> v1->v2: >> Rename 'start_pfn' to 'iteration_start_pfn' and change commit messages. >> >>   mm/compaction.c | 7 +++---- >>   1 file changed, 3 insertions(+), 4 deletions(-) >> >> diff --git a/mm/compaction.c b/mm/compaction.c >> index 176dcded298e..ccd27c739fd6 100644 >> --- a/mm/compaction.c >> +++ b/mm/compaction.c >> @@ -2272,7 +2272,7 @@ compact_zone(struct compact_control *cc, struct >> capture_control *capc) >>       while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) { >>           int err; >> -        unsigned long start_pfn = cc->migrate_pfn; >> +        unsigned long iteration_start_pfn = cc->migrate_pfn; >>           /* >>            * Avoid multiple rescans which can happen if a page cannot be >> @@ -2284,7 +2284,7 @@ compact_zone(struct compact_control *cc, struct >> capture_control *capc) >>            */ >>           cc->rescan = false; >>           if (pageblock_start_pfn(last_migrated_pfn) == >> -            pageblock_start_pfn(start_pfn)) { >> +            pageblock_start_pfn(iteration_start_pfn)) { >>               cc->rescan = true; >>           } >> @@ -2308,8 +2308,7 @@ compact_zone(struct compact_control *cc, struct >> capture_control *capc) >>               goto check_drain; >>           case ISOLATE_SUCCESS: >>               update_cached = false; >> -            last_migrated_pfn = start_pfn; >> -            ; >> +            last_migrated_pfn = iteration_start_pfn; >>           } >>           err = migrate_pages(&cc->migratepages, compaction_alloc, >> > >