From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933354AbaD2Ikj (ORCPT ); Tue, 29 Apr 2014 04:40:39 -0400 Received: from cantor2.suse.de ([195.135.220.15]:46680 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932529AbaD2Ikh (ORCPT ); Tue, 29 Apr 2014 04:40:37 -0400 Message-ID: <535F657D.3060809@suse.cz> Date: Tue, 29 Apr 2014 10:40:29 +0200 From: Vlastimil Babka User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.3.0 MIME-Version: 1.0 To: Joonsoo Kim 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() 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> <20140425082941.GA11428@js1304-P5Q-DELUXE> In-Reply-To: <20140425082941.GA11428@js1304-P5Q-DELUXE> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/25/2014 10:29 AM, Joonsoo Kim wrote: > 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. :) Great, thanks! > 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 Acked-by: Vlastimil Babka > 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; >