user/sven/linux.git/mm/compaction.c, branch v3.0.9

mm: compaction: abort compaction if too many pages are isolated and caller is asynchronous V2

2011-06-16T03:04:02Z

Asynchronous compaction is used when promoting to huge pages. This is all very nice but if there are a number of processes in compacting memory, a large number of pages can be isolated. An "asynchronous" process can stall for long periods of time as a result with a user reporting that firefox can stall for 10s of seconds. This patch aborts asynchronous compaction if too many pages are isolated as it's better to fail a hugepage promotion than stall a process. [minchan.kim@gmail.com: return COMPACT_PARTIAL for abort] Reported-and-tested-by: Ury Stankevich Signed-off-by: Mel Gorman Reviewed-by: Minchan Kim Reviewed-by: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: compaction: ensure that the compaction free scanner does not move to the next zone

2011-06-16T03:04:02Z

Compaction works with two scanners, a migration and a free scanner. When the scanners crossover, migration within the zone is complete. The location of the scanner is recorded on each cycle to avoid excesive scanning. When a zone is small and mostly reserved, it's very easy for the migration scanner to be close to the end of the zone. Then the following situation can occurs o migration scanner isolates some pages near the end of the zone o free scanner starts at the end of the zone but finds that the migration scanner is already there o free scanner gets reinitialised for the next cycle as cc->migrate_pfn + pageblock_nr_pages moving the free scanner into the next zone o migration scanner moves into the next zone When this happens, NR_ISOLATED accounting goes haywire because some of the accounting happens against the wrong zone. One zones counter remains positive while the other goes negative even though the overall global count is accurate. This was reported on X86-32 with !SMP because !SMP allows the negative counters to be visible. The fact that it is the bug should theoritically be possible there. Signed-off-by: Mel Gorman Reviewed-by: Minchan Kim Reviewed-by: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

compaction: checks correct fragmentation index

2011-06-16T03:04:02Z

fragmentation_index() returns -1000 when the allocation might succeed This doesn't match the comment and code in compaction_suitable(). I thought compaction_suitable should return COMPACT_PARTIAL in -1000 case, because in this case allocation could succeed depending on watermarks. The impact of this is that compaction starts and compact_finished() is called which rechecks the watermarks and the free lists. It should have the same result in that compaction should not start but is more expensive. Acked-by: Mel Gorman Signed-off-by: Shaohua Li Cc: Minchan Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: compaction: fix special case -1 order checks

2011-06-16T03:04:00Z

Commit 56de7263fcf3 ("mm: compaction: direct compact when a high-order allocation fails") introduced a check for cc->order == -1 in compact_finished. We should continue compacting in that case because the request came from userspace and there is no particular order to compact for. Similar check has been added by 82478fb7 (mm: compaction: prevent division-by-zero during user-requested compaction) for compaction_suitable. The check is, however, done after zone_watermark_ok which uses order as a right hand argument for shifts. Not only watermark check is pointless if we can break out without it but it also uses 1 << -1 which is not well defined (at least from C standard). Let's move the -1 check above zone_watermark_ok. [minchan.kim@gmail.com> - caught compaction_suitable] Signed-off-by: Michal Hocko Cc: Mel Gorman Reviewed-by: Minchan Kim Reviewed-by: KAMEZAWA Hiroyuki Acked-by: Mel Gorman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: compaction: minimise the time IRQs are disabled while isolating pages for migration

2011-03-23T00:44:05Z

compaction_alloc() isolates pages for migration in isolate_migratepages. While it's scanning, IRQs are disabled on the mistaken assumption the scanning should be short. Tests show this to be true for the most part but contention times on the LRU lock can be increased. Before this patch, the IRQ disabled times for a simple test looked like Total sampled time IRQs off (not real total time): 5493 Event shrink_inactive_list..shrink_zone 1596 us count 1 Event shrink_inactive_list..shrink_zone 1530 us count 1 Event shrink_inactive_list..shrink_zone 956 us count 1 Event shrink_inactive_list..shrink_zone 541 us count 1 Event shrink_inactive_list..shrink_zone 531 us count 1 Event split_huge_page..add_to_swap 232 us count 1 Event save_args..call_softirq 36 us count 1 Event save_args..call_softirq 35 us count 2 Event __wake_up..__wake_up 1 us count 1 This patch reduces the worst-case IRQs-disabled latencies by releasing the lock every SWAP_CLUSTER_MAX pages that are scanned and releasing the CPU if necessary. The cost of this is that the processing performing compaction will be slower but IRQs being disabled for too long a time has worse consequences as the following report shows; Total sampled time IRQs off (not real total time): 4367 Event shrink_inactive_list..shrink_zone 881 us count 1 Event shrink_inactive_list..shrink_zone 875 us count 1 Event shrink_inactive_list..shrink_zone 868 us count 1 Event shrink_inactive_list..shrink_zone 555 us count 1 Event split_huge_page..add_to_swap 495 us count 1 Event compact_zone..compact_zone_order 269 us count 1 Event split_huge_page..add_to_swap 266 us count 1 Event shrink_inactive_list..shrink_zone 85 us count 1 Event save_args..call_softirq 36 us count 2 Event __wake_up..__wake_up 1 us count 1 [akpm@linux-foundation.org: simplify with s/unlocked/locked/] Signed-off-by: Andrea Arcangeli Signed-off-by: Mel Gorman Cc: Johannes Weiner Cc: Arthur Marsh Cc: Clemens Ladisch Cc: KAMEZAWA Hiroyuki Cc: Minchan Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: compaction: minimise the time IRQs are disabled while isolating free pages

2011-03-23T00:44:05Z

compaction_alloc() isolates free pages to be used as migration targets. While its scanning, IRQs are disabled on the mistaken assumption the scanning should be short. Analysis showed that IRQs were in fact being disabled for substantial time. A simple test was run using large anonymous mappings with transparent hugepage support enabled to trigger frequent compactions. A monitor sampled what the worst IRQ-off latencies were and a post-processing tool found the following; Total sampled time IRQs off (not real total time): 22355 Event compaction_alloc..compaction_alloc 8409 us count 1 Event compaction_alloc..compaction_alloc 7341 us count 1 Event compaction_alloc..compaction_alloc 2463 us count 1 Event compaction_alloc..compaction_alloc 2054 us count 1 Event shrink_inactive_list..shrink_zone 1864 us count 1 Event shrink_inactive_list..shrink_zone 88 us count 1 Event save_args..call_softirq 36 us count 1 Event save_args..call_softirq 35 us count 2 Event __make_request..__blk_run_queue 24 us count 1 Event __alloc_pages_nodemask..__alloc_pages_nodemask 6 us count 1 i.e. compaction is disabled IRQs for a prolonged period of time - 8ms in one instance. The full report generated by the tool can be found at http://www.csn.ul.ie/~mel/postings/minfree-20110225/irqsoff-vanilla-micro.report This patch reduces the time IRQs are disabled by simply disabling IRQs at the last possible minute. An updated IRQs-off summary report then looks like; Total sampled time IRQs off (not real total time): 5493 Event shrink_inactive_list..shrink_zone 1596 us count 1 Event shrink_inactive_list..shrink_zone 1530 us count 1 Event shrink_inactive_list..shrink_zone 956 us count 1 Event shrink_inactive_list..shrink_zone 541 us count 1 Event shrink_inactive_list..shrink_zone 531 us count 1 Event split_huge_page..add_to_swap 232 us count 1 Event save_args..call_softirq 36 us count 1 Event save_args..call_softirq 35 us count 2 Event __wake_up..__wake_up 1 us count 1 A full report is again available at http://www.csn.ul.ie/~mel/postings/minfree-20110225/irqsoff-minimiseirq-free-v1r4-micro.report As should be obvious, IRQ disabled latencies due to compaction are almost elimimnated for this particular test. [aarcange@redhat.com: Fix initialisation of isolated] Signed-off-by: Mel Gorman Acked-by: Johannes Weiner Reviewed-by: KAMEZAWA Hiroyuki Reviewed-by: Minchan Kim Acked-by: Andrea Arcangeli Cc: Arthur Marsh Cc: Clemens Ladisch Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/compaction: check migrate_pages's return value instead of list_empty()

2011-03-23T00:44:00Z

Many migrate_page's caller check return value instead of list_empy by cf608ac19c ("mm: compaction: fix COMPACTPAGEFAILED counting"). This patch makes compaction's migrate_pages consistent with others. This patch should not change old behavior. Signed-off-by: Minchan Kim Cc: Mel Gorman Cc: Andrea Arcangeli Cc: Christoph Lameter Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: compaction: prevent kswapd compacting memory to reduce CPU usage

2011-03-23T00:44:00Z

This patch reverts 5a03b051 ("thp: use compaction in kswapd for GFP_ATOMIC order > 0") due to reports stating that kswapd CPU usage was higher and IRQs were being disabled more frequently. This was reported at http://www.spinics.net/linux/fedora/alsa-user/msg09885.html. Without this patch applied, CPU usage by kswapd hovers around the 20% mark according to the tester (Arthur Marsh: http://www.spinics.net/linux/fedora/alsa-user/msg09899.html). With this patch applied, it's around 2%. The problem is not related to THP which specifies __GFP_NO_KSWAPD but is triggered by high-order allocations hitting the low watermark for their order and waking kswapd on kernels with CONFIG_COMPACTION set. The most common trigger for this is network cards configured for jumbo frames but it's also possible it'll be triggered by fork-heavy workloads (order-1) and some wireless cards which depend on order-1 allocations. The symptoms for the user will be high CPU usage by kswapd in low-memory situations which could be confused with another writeback problem. While a patch like 5a03b051 may be reintroduced in the future, this patch plays it safe for now and reverts it. [mel@csn.ul.ie: Beefed up the changelog] Signed-off-by: Andrea Arcangeli Signed-off-by: Mel Gorman Reported-by: Arthur Marsh Tested-by: Arthur Marsh Cc: [2.6.38.1] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: compaction: prevent division-by-zero during user-requested compaction

2011-01-21T01:02:05Z

Up until 3e7d344 ("mm: vmscan: reclaim order-0 and use compaction instead of lumpy reclaim"), compaction skipped calculating the fragmentation index of a zone when compaction was explicitely requested through the procfs knob. However, when compaction_suitable was introduced, it did not come with an extra check for order == -1, set on explicit compaction requests, and passed this order on to the fragmentation index calculation, where it overshifts the number of requested pages, leading to a division by zero. This patch makes sure that order == -1 is recognized as the flag it is rather than passing it along as valid order parameter. [akpm@linux-foundation.org: add comment, per Mel] Signed-off-by: Johannes Weiner Reviewed-by: Mel Gorman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

thp: use compaction for all allocation orders

2011-01-14T01:32:46Z

It makes no sense not to enable compaction for small order pages as we don't want to end up with bad order 2 allocations and good and graceful order 9 allocations. Signed-off-by: Andrea Arcangeli Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds