On Tue, 21 Jun 2016, Vlastimil Babka wrote: > > 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. > Indeed, I hadn't noticed the differences between Linus's tree and -mm. Thanks very much for pointing it out. My interest is to eventually backport this to a much older kernel where we suffer from the same issue: it seems that we have always not terminated the freeing scanner when splitting the free page fails and we feel it because some of our systems have 128GB zones and migrate_pages() can call compaction_alloc() several times if it keeps getting -EAGAIN. It's very expensive. I'm not sure we should label it as a -fix for mm-compaction-split-freepages-without-holding-the-zone-lock.patch since the problem this patch is addressing has seemingly existed for years. Perhaps it would be better to have two patches, one as a -fix and then the abort on page split failure on top. I'll send out a two patch series in this form. > > 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? > Eek, maybe. The condition should only work if we terminated early because - need_resched() or zone->lock contention for MIGRATE_ASYNC, or - __isolate_free_page() fails. And the latter can only fail because of this (somewhat arbitrary) split watermark check. I'll rename it because it includes both, but I thought the next immediate condition check for cc->contended and its comment was explanatory enough. > > + 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. > Good point, thanks. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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