From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751587AbcFUMFY (ORCPT ); Tue, 21 Jun 2016 08:05:24 -0400 Received: from mx2.suse.de ([195.135.220.15]:43848 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750931AbcFUMFW (ORCPT ); Tue, 21 Jun 2016 08:05:22 -0400 Subject: Re: [patch] mm, compaction: abort free scanner if split fails To: David Rientjes , Andrew Morton References: <4f5ba93e-8bf0-151e-57eb-cad1a4823b9e@suse.cz> Cc: Mel Gorman , Hugh Dickins , Joonsoo Kim , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Minchan Kim From: Vlastimil Babka Message-ID: <5783072b-0341-dccb-8f07-c92230964d83@suse.cz> Date: Tue, 21 Jun 2016 13:43:47 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/21/2016 12:27 AM, David Rientjes wrote: > If the memory compaction free scanner cannot successfully split a free > page (only possible due to per-zone low watermark), terminate the free > scanner rather than continuing to scan memory needlessly. > > If the per-zone watermark is insufficient for a free page of > order <= cc->order, then terminate the scanner since future splits will > also likely fail. > > This prevents the compaction freeing scanner from scanning all memory on > very large zones (very noticeable for zones > 128GB, for instance) when > all splits will likely fail. > > Signed-off-by: David Rientjes Acked-by: Vlastimil Babka But some notes below. > --- > mm/compaction.c | 49 +++++++++++++++++++++++++++++-------------------- > 1 file changed, 29 insertions(+), 20 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -494,24 +494,22 @@ static unsigned long isolate_freepages_block(struct compact_control *cc, > > /* Found a free page, will break it into order-0 pages */ > order = page_order(page); > - isolated = __isolate_free_page(page, page_order(page)); > + isolated = __isolate_free_page(page, order); > + if (!isolated) > + break; This seems to fix as a side-effect a bug in Joonsoo's mmotm patch mm-compaction-split-freepages-without-holding-the-zone-lock.patch, that Minchan found: http://marc.info/?l=linux-mm&m=146607176528495&w=2 So it should be noted somewhere so they are merged together. Or Joonsoo posts an isolated fix and this patch has to rebase. > set_page_private(page, order); > total_isolated += isolated; > list_add_tail(&page->lru, freelist); > > - /* If a page was split, advance to the end of it */ > - if (isolated) { > - cc->nr_freepages += isolated; > - if (!strict && > - cc->nr_migratepages <= cc->nr_freepages) { > - blockpfn += isolated; > - break; > - } > - > - blockpfn += isolated - 1; > - cursor += isolated - 1; > - continue; > + /* Advance to the end of split page */ > + cc->nr_freepages += isolated; > + if (!strict && cc->nr_migratepages <= cc->nr_freepages) { > + blockpfn += isolated; > + break; > } > + blockpfn += isolated - 1; > + cursor += isolated - 1; > + continue; > > isolate_fail: > if (strict) > @@ -521,6 +519,9 @@ isolate_fail: > > } > > + if (locked) > + spin_unlock_irqrestore(&cc->zone->lock, flags); > + > /* > * There is a tiny chance that we have read bogus compound_order(), > * so be careful to not go outside of the pageblock. > @@ -542,9 +543,6 @@ isolate_fail: > if (strict && blockpfn < end_pfn) > total_isolated = 0; > > - if (locked) > - spin_unlock_irqrestore(&cc->zone->lock, flags); > - > /* Update the pageblock-skip if the whole pageblock was scanned */ > if (blockpfn == end_pfn) > update_pageblock_skip(cc, valid_page, total_isolated, false); > @@ -622,7 +620,7 @@ isolate_freepages_range(struct compact_control *cc, > */ > } > > - /* split_free_page does not map the pages */ > + /* __isolate_free_page() does not map the pages */ > map_pages(&freelist); > > if (pfn < end_pfn) { > @@ -1071,6 +1069,7 @@ static void isolate_freepages(struct compact_control *cc) > block_end_pfn = block_start_pfn, > block_start_pfn -= pageblock_nr_pages, > isolate_start_pfn = block_start_pfn) { > + unsigned long isolated; > > /* > * This can iterate a massively long zone without finding any > @@ -1095,8 +1094,12 @@ static void isolate_freepages(struct compact_control *cc) > continue; > > /* Found a block suitable for isolating free pages from. */ > - isolate_freepages_block(cc, &isolate_start_pfn, > - block_end_pfn, freelist, false); > + isolated = isolate_freepages_block(cc, &isolate_start_pfn, > + block_end_pfn, freelist, false); > + /* If free page split failed, do not continue needlessly */ More accurately, free page isolation failed? > + if (!isolated && isolate_start_pfn < block_end_pfn && > + cc->nr_freepages <= cc->nr_migratepages) > + break; > > /* > * If we isolated enough freepages, or aborted due to async > @@ -1124,7 +1127,7 @@ static void isolate_freepages(struct compact_control *cc) > } > } > > - /* split_free_page does not map the pages */ > + /* __isolate_free_page() does not map the pages */ > map_pages(freelist); > > /* > @@ -1703,6 +1706,12 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order, > continue; > } > > + /* Don't attempt compaction if splitting free page will fail */ > + if (!zone_watermark_ok(zone, 0, > + low_wmark_pages(zone) + (1 << order), > + 0, 0)) > + continue; > + Please don't add this, compact_zone already checks this via compaction_suitable() (and the usual 2 << order gap), so this is adding yet another watermark check with a different kind of gap. Thanks. > status = compact_zone_order(zone, order, gfp_mask, mode, > &zone_contended, alloc_flags, > ac_classzone_idx(ac)); >