Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752390AbaDYI2s (ORCPT ); Fri, 25 Apr 2014 04:28:48 -0400 Received: from lgeamrelo04.lge.com ([156.147.1.127]:45776 "EHLO lgeamrelo04.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750719AbaDYI2m (ORCPT ); Fri, 25 Apr 2014 04:28:42 -0400 X-Original-SENDERIP: 10.177.220.145 X-Original-MAILFROM: iamjoonsoo.kim@lge.com Date: Fri, 25 Apr 2014 17:29:41 +0900 From: Joonsoo Kim To: Vlastimil Babka Cc: Minchan Kim , Andrew Morton , Mel Gorman , Heesub Shin , LKML , Linux Memory Management List , Dongjun Shin , Sunghwan Yun , Bartlomiej Zolnierkiewicz , Michal Nazarewicz , Naoya Horiguchi , Christoph Lameter , Rik van Riel Subject: Re: [PATCH 2/2] mm/compaction: cleanup isolate_freepages() Message-ID: <20140425082941.GA11428@js1304-P5Q-DELUXE> References: <20140421124146.c8beacf0d58aafff2085a461@linux-foundation.org> <535590FC.10607@suse.cz> <20140421235319.GD7178@bbox> <53560D3F.2030002@suse.cz> <20140422065224.GE24292@bbox> <53566BEA.2060808@suse.cz> <20140423025806.GA11184@js1304-P5Q-DELUXE> <53576C08.2080003@suse.cz> <5357CEB2.1070900@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5357CEB2.1070900@suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 23, 2014 at 04:31:14PM +0200, Vlastimil Babka wrote: > >>> > >>> Hello, > >>> > >>> How about doing more clean-up at this time? > >>> > >>> What I did is that taking end_pfn out of the loop and consider zone > >>> boundary once. After then, we just subtract pageblock_nr_pages on > >>> every iteration. With this change, we can remove local variable, z_end_pfn. > >>> Another things I did are removing max() operation and un-needed > >>> assignment to isolate variable. > >>> > >>> Thanks. > >>> > >>> --------->8------------ > >>> diff --git a/mm/compaction.c b/mm/compaction.c > >>> index 1c992dc..95a506d 100644 > >>> --- a/mm/compaction.c > >>> +++ b/mm/compaction.c > >>> @@ -671,10 +671,10 @@ static void isolate_freepages(struct zone *zone, > >>> struct compact_control *cc) > >>> { > >>> struct page *page; > >>> - unsigned long pfn; /* scanning cursor */ > >>> + unsigned long pfn; /* start of scanning window */ > >>> + unsigned long end_pfn; /* end of scanning window */ > >>> unsigned long low_pfn; /* lowest pfn scanner is able to scan */ > >>> unsigned long next_free_pfn; /* start pfn for scaning at next round */ > >>> - unsigned long z_end_pfn; /* zone's end pfn */ > >>> int nr_freepages = cc->nr_freepages; > >>> struct list_head *freelist = &cc->freepages; > >>> > >>> @@ -688,15 +688,16 @@ static void isolate_freepages(struct zone *zone, > >>> * is using. > >>> */ > >>> pfn = cc->free_pfn & ~(pageblock_nr_pages-1); > >>> - low_pfn = ALIGN(cc->migrate_pfn + 1, pageblock_nr_pages); > >>> > >>> /* > >>> - * Seed the value for max(next_free_pfn, pfn) updates. If no pages are > >>> - * isolated, the pfn < low_pfn check will kick in. > >>> + * Take care when isolating in last pageblock of a zone which > >>> + * ends in the middle of a pageblock. > >>> */ > >>> - next_free_pfn = 0; > >>> + end_pfn = min(pfn + pageblock_nr_pages, zone_end_pfn(zone)); > >>> + low_pfn = ALIGN(cc->migrate_pfn + 1, pageblock_nr_pages); > >>> > >>> - z_end_pfn = zone_end_pfn(zone); > >>> + /* If no pages are isolated, the pfn < low_pfn check will kick in. */ > >>> + next_free_pfn = 0; > >>> > >>> /* > >>> * Isolate free pages until enough are available to migrate the > >>> @@ -704,9 +705,8 @@ static void isolate_freepages(struct zone *zone, > >>> * and free page scanners meet or enough free pages are isolated. > >>> */ > >>> for (; pfn >= low_pfn && cc->nr_migratepages > nr_freepages; > >>> - pfn -= pageblock_nr_pages) { > >>> + pfn -= pageblock_nr_pages, end_pfn -= pageblock_nr_pages) { > >> > >> If zone_end_pfn was in the middle of a pageblock, then your end_pfn will > >> always be in the middle of a pageblock and you will not scan half of all > >> pageblocks. > >> > > > > Okay. I think a way to fix it. > > By assigning pfn(start of scanning window) to > > end_pfn(end of scanning window) for the next loop, we can solve the problem > > you mentioned. How about below? > > > > - pfn -= pageblock_nr_pages, end_pfn -= pageblock_nr_pages) { > > + end_pfn = pfn, pfn -= pageblock_nr_pages) { > > Hm that's perhaps a bit subtle but it would work. > Maybe better names for pfn and end_pfn would be block_start_pfn and > block_end_pfn. And in those comments, s/scanning window/current pageblock/. > And please don't move the low_pfn assignment like you did. The comment > above the original location explains it, the comment above the new > location doesn't. It's use in the loop is also related to 'pfn', not > 'end_pfn'. Okay. Following patch solves all your concerns. End result looks so nice to me. :) Thanks. --------->8---------------- >From ae653cf8b9f8c7423cad73af38cde94eec564b50 Mon Sep 17 00:00:00 2001 From: Joonsoo Kim Date: Fri, 25 Apr 2014 17:12:58 +0900 Subject: [PATCH] mm-compaction-cleanup-isolate_freepages-fix3 What I did here is taking end_pfn out of the loop and considering zone boundary once. After then, we can just set previous pfn to end_pfn on every iteration to move scanning window. With this change, we can remove local variable, z_end_pfn. Another things I did are removing max() operation and un-needed assignment to isolate variable. In addition, I change both the variable names, from pfn and end_pfn to block_start_pfn and block_end_pfn, respectively. They represent their meaning perfectly. Signed-off-by: Joonsoo Kim diff --git a/mm/compaction.c b/mm/compaction.c index 1c992dc..ba80bea 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -671,10 +671,10 @@ static void isolate_freepages(struct zone *zone, struct compact_control *cc) { struct page *page; - unsigned long pfn; /* scanning cursor */ + unsigned long block_start_pfn; /* start of current pageblock */ + unsigned long block_end_pfn; /* end of current pageblock */ unsigned long low_pfn; /* lowest pfn scanner is able to scan */ unsigned long next_free_pfn; /* start pfn for scaning at next round */ - unsigned long z_end_pfn; /* zone's end pfn */ int nr_freepages = cc->nr_freepages; struct list_head *freelist = &cc->freepages; @@ -682,31 +682,33 @@ static void isolate_freepages(struct zone *zone, * Initialise the free scanner. The starting point is where we last * successfully isolated from, zone-cached value, or the end of the * zone when isolating for the first time. We need this aligned to - * the pageblock boundary, because we do pfn -= pageblock_nr_pages - * in the for loop. + * the pageblock boundary, because we do + * block_start_pfn -= pageblock_nr_pages in the for loop. + * For ending point, take care when isolating in last pageblock of a + * a zone which ends in the middle of a pageblock. * The low boundary is the end of the pageblock the migration scanner * is using. */ - pfn = cc->free_pfn & ~(pageblock_nr_pages-1); + block_start_pfn = cc->free_pfn & ~(pageblock_nr_pages-1); + block_end_pfn = min(block_start_pfn + pageblock_nr_pages, + zone_end_pfn(zone)); low_pfn = ALIGN(cc->migrate_pfn + 1, pageblock_nr_pages); /* - * Seed the value for max(next_free_pfn, pfn) updates. If no pages are - * isolated, the pfn < low_pfn check will kick in. + * If no pages are isolated, the block_start_pfn < low_pfn check + * will kick in. */ next_free_pfn = 0; - z_end_pfn = zone_end_pfn(zone); - /* * Isolate free pages until enough are available to migrate the * pages on cc->migratepages. We stop searching if the migrate * and free page scanners meet or enough free pages are isolated. */ - for (; pfn >= low_pfn && cc->nr_migratepages > nr_freepages; - pfn -= pageblock_nr_pages) { + for (;block_start_pfn >= low_pfn && cc->nr_migratepages > nr_freepages; + block_end_pfn = block_start_pfn, + block_start_pfn -= pageblock_nr_pages) { unsigned long isolated; - unsigned long end_pfn; /* * This can iterate a massively long zone without finding any @@ -715,7 +717,7 @@ static void isolate_freepages(struct zone *zone, */ cond_resched(); - if (!pfn_valid(pfn)) + if (!pfn_valid(block_start_pfn)) continue; /* @@ -725,7 +727,7 @@ static void isolate_freepages(struct zone *zone, * i.e. it's possible that all pages within a zones range of * pages do not belong to a single zone. */ - page = pfn_to_page(pfn); + page = pfn_to_page(block_start_pfn); if (page_zone(page) != zone) continue; @@ -738,15 +740,8 @@ static void isolate_freepages(struct zone *zone, continue; /* Found a block suitable for isolating free pages from */ - isolated = 0; - - /* - * Take care when isolating in last pageblock of a zone which - * ends in the middle of a pageblock. - */ - end_pfn = min(pfn + pageblock_nr_pages, z_end_pfn); - isolated = isolate_freepages_block(cc, pfn, end_pfn, - freelist, false); + isolated = isolate_freepages_block(cc, block_start_pfn, + block_end_pfn, freelist, false); nr_freepages += isolated; /* @@ -754,9 +749,9 @@ static void isolate_freepages(struct zone *zone, * looking for free pages, the search will restart here as * page migration may have returned some pages to the allocator */ - if (isolated) { + if (isolated && next_free_pfn == 0) { cc->finished_update_free = true; - next_free_pfn = max(next_free_pfn, pfn); + next_free_pfn = block_start_pfn; } } @@ -767,7 +762,7 @@ static void isolate_freepages(struct zone *zone, * If we crossed the migrate scanner, we want to keep it that way * so that compact_finished() may detect this */ - if (pfn < low_pfn) + if (block_start_pfn < low_pfn) next_free_pfn = cc->migrate_pfn; cc->free_pfn = next_free_pfn; -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/