On Fri, May 04, 2012 at 04:03:25PM +0200, Bartlomiej Zolnierkiewicz wrote: > From: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx> > Subject: [PATCH v6] mm: compaction: handle incorrect MIGRATE_UNMOVABLE type pageblocks > > When MIGRATE_UNMOVABLE pages are freed from MIGRATE_UNMOVABLE > type pageblock (and some MIGRATE_MOVABLE pages are left in it) > waiting until an allocation takes ownership of the block may > take too long. The type of the pageblock remains unchanged > so the pageblock cannot be used as a migration target during > compaction. > > Fix it by: > > * Adding enum compact_mode (COMPACT_ASYNC_[MOVABLE,UNMOVABLE], > and COMPACT_SYNC) and then converting sync field in struct > compact_control to use it. > > * Adding nr_pageblocks_scanned and nr_pageblocks_skipped fields > to struct compact_control and tracking how many destination > pageblocks were scanned during compaction and how many of them > were of MIGRATE_UNMOVABLE type. If COMPACT_ASYNC_MOVABLE mode > compaction ran fully in try_to_compact_pages() (COMPACT_COMPLETE) > it implies that there is not a suitable page for allocation. > In this case then check how if there were enough MIGRATE_UNMOVABLE > pageblocks to try a second pass in COMPACT_ASYNC_UNMOVABLE mode. > > * Scanning the MIGRATE_UNMOVABLE pageblocks (during COMPACT_SYNC > and COMPACT_ASYNC_UNMOVABLE compaction modes) and building > a count based on finding PageBuddy pages, page_count(page) == 0 > or PageLRU pages. If all pages within the MIGRATE_UNMOVABLE > pageblock are in one of those three sets change the whole > pageblock type to MIGRATE_MOVABLE. > > > My particular test case (on a ARM EXYNOS4 device with 512 MiB, > which means 131072 standard 4KiB pages in 'Normal' zone) is to: > - allocate 120000 pages for kernel's usage > - free every second page (60000 pages) of memory just allocated > - allocate and use 60000 pages from user space > - free remaining 60000 pages of kernel memory > (now we have fragmented memory occupied mostly by user space pages) > - try to allocate 100 order-9 (2048 KiB) pages for kernel's usage > > The results: > - with compaction disabled I get 11 successful allocations > - with compaction enabled - 14 successful allocations > - with this patch I'm able to get all 100 successful allocations > > > NOTE: If we can make kswapd aware of order-0 request during > compaction, we can enhance kswapd with changing mode to > COMPACT_ASYNC_FULL (COMPACT_ASYNC_MOVABLE + COMPACT_ASYNC_UNMOVABLE). > Please see the following thread: > > http://marc.info/?l=linux-mm&m=133552069417068&w=2 > > Cc: Mel Gorman <mgorman@xxxxxxx> > Cc: Minchan Kim <minchan@xxxxxxxxxx> > Cc: Rik van Riel <riel@xxxxxxxxxx> > Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> > Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx> > Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx> > > <SNIP> > > @@ -750,6 +816,8 @@ > struct zoneref *z; > struct zone *zone; > int rc = COMPACT_SKIPPED; > + unsigned long nr_pageblocks_scanned = 0, nr_pageblocks_skipped = 0; > + enum compact_mode mode = sync ? COMPACT_SYNC : COMPACT_ASYNC_MOVABLE; > > /* > * Check whether it is worth even starting compaction. The order check is > @@ -765,13 +833,22 @@ > for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx, > nodemask) { > int status; > - > - status = compact_zone_order(zone, order, gfp_mask, sync); > +retry: > + status = compact_zone_order(zone, order, gfp_mask, mode, > + &nr_pageblocks_scanned, &nr_pageblocks_skipped); > rc = max(status, rc); > > /* If a normal allocation would succeed, stop compacting */ > if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0)) > break; > + > + if (rc == COMPACT_COMPLETE && mode == COMPACT_ASYNC_MOVABLE) { > + if (nr_pageblocks_scanned && nr_pageblocks_skipped) { > + mode = COMPACT_ASYNC_UNMOVABLE; > + goto retry; > + } > + } else > + mode = sync ? COMPACT_SYNC : COMPACT_ASYNC_MOVABLE; Minor nit but if you moved this line above the retry: then the else block would be necessary. It would not be necessary to initialise mode at the start of the function either. Otherwise I didn't spot anything. Acked-by: Mel Gorman <mgorman@xxxxxxx> -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>