user/sven/linux.git/include/linux/compaction.h, branch v3.9

mm: compaction: make __compact_pgdat() and compact_pgdat() return void

2013-02-24T01:50:10Z

These functions always return 0. Formalise this. Cc: Jason Liu Cc: KAMEZAWA Hiroyuki Cc: Mel Gorman Cc: Minchan Kim Cc: Rik van Riel Acked-by: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: compaction: Partially revert capture of suitable high-order page

2013-01-11T17:02:00Z

Eric Wong reported on 3.7 and 3.8-rc2 that ppoll() got stuck when waiting for POLLIN on a local TCP socket. It was easier to trigger if there was disk IO and dirty pages at the same time and he bisected it to commit 1fb3f8ca0e92 ("mm: compaction: capture a suitable high-order page immediately when it is made available"). The intention of that patch was to improve high-order allocations under memory pressure after changes made to reclaim in 3.6 drastically hurt THP allocations but the approach was flawed. For Eric, the problem was that page->pfmemalloc was not being cleared for captured pages leading to a poor interaction with swap-over-NFS support causing the packets to be dropped. However, I identified a few more problems with the patch including the fact that it can increase contention on zone->lock in some cases which could result in async direct compaction being aborted early. In retrospect the capture patch took the wrong approach. What it should have done is mark the pageblock being migrated as MIGRATE_ISOLATE if it was allocating for THP and avoided races that way. While the patch was showing to improve allocation success rates at the time, the benefit is marginal given the relative complexity and it should be revisited from scratch in the context of the other reclaim-related changes that have taken place since the patch was first written and tested. This patch partially reverts commit 1fb3f8ca "mm: compaction: capture a suitable high-order page immediately when it is made available". Reported-and-tested-by: Eric Wong Tested-by: Eric Dumazet Cc: stable@vger.kernel.org Signed-off-by: Mel Gorman Signed-off-by: Linus Torvalds

mm: compaction: clear PG_migrate_skip based on compaction and reclaim activity

2012-10-09T07:22:51Z

Compaction caches if a pageblock was scanned and no pages were isolated so that the pageblocks can be skipped in the future to reduce scanning. This information is not cleared by the page allocator based on activity due to the impact it would have to the page allocator fast paths. Hence there is a requirement that something clear the cache or pageblocks will be skipped forever. Currently the cache is cleared if there were a number of recent allocation failures and it has not been cleared within the last 5 seconds. Time-based decisions like this are terrible as they have no relationship to VM activity and is basically a big hammer. Unfortunately, accurate heuristics would add cost to some hot paths so this patch implements a rough heuristic. There are two cases where the cache is cleared. 1. If a !kswapd process completes a compaction cycle (migrate and free scanner meet), the zone is marked compact_blockskip_flush. When kswapd goes to sleep, it will clear the cache. This is expected to be the common case where the cache is cleared. It does not really matter if kswapd happens to be asleep or going to sleep when the flag is set as it will be woken on the next allocation request. 2. If there have been multiple failures recently and compaction just finished being deferred then a process will clear the cache and start a full scan. This situation happens if there are multiple high-order allocation requests under heavy memory pressure. The clearing of the PG_migrate_skip bits and other scans is inherently racy but the race is harmless. For allocations that can fail such as THP, they will simply fail. For requests that cannot fail, they will retry the allocation. Tests indicated that scanning rates were roughly similar to when the time-based heuristic was used and the allocation success rates were similar. Signed-off-by: Mel Gorman Cc: Rik van Riel Cc: Richard Davies Cc: Shaohua Li Cc: Avi Kivity Cc: Rafael Aquini Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: compaction: capture a suitable high-order page immediately when it is made available

2012-10-09T07:22:21Z

While compaction is migrating pages to free up large contiguous blocks for allocation it races with other allocation requests that may steal these blocks or break them up. This patch alters direct compaction to capture a suitable free page as soon as it becomes available to reduce this race. It uses similar logic to split_free_page() to ensure that watermarks are still obeyed. Signed-off-by: Mel Gorman Reviewed-by: Rik van Riel Reviewed-by: Minchan Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: compaction: Abort async compaction if locks are contended or taking too long

2012-08-21T23:45:03Z

Jim Schutt reported a problem that pointed at compaction contending heavily on locks. The workload is straight-forward and in his own words; The systems in question have 24 SAS drives spread across 3 HBAs, running 24 Ceph OSD instances, one per drive. FWIW these servers are dual-socket Intel 5675 Xeons w/48 GB memory. I've got ~160 Ceph Linux clients doing dd simultaneously to a Ceph file system backed by 12 of these servers. Early in the test everything looks fine procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 31 15 0 287216 576 38606628 0 0 2 1158 2 14 1 3 95 0 0 27 15 0 225288 576 38583384 0 0 18 2222016 203357 134876 11 56 17 15 0 28 17 0 219256 576 38544736 0 0 11 2305932 203141 146296 11 49 23 17 0 6 18 0 215596 576 38552872 0 0 7 2363207 215264 166502 12 45 22 20 0 22 18 0 226984 576 38596404 0 0 3 2445741 223114 179527 12 43 23 22 0 and then it goes to pot procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 163 8 0 464308 576 36791368 0 0 11 22210 866 536 3 13 79 4 0 207 14 0 917752 576 36181928 0 0 712 1345376 134598 47367 7 90 1 2 0 123 12 0 685516 576 36296148 0 0 429 1386615 158494 60077 8 84 5 3 0 123 12 0 598572 576 36333728 0 0 1107 1233281 147542 62351 7 84 5 4 0 622 7 0 660768 576 36118264 0 0 557 1345548 151394 59353 7 85 4 3 0 223 11 0 283960 576 36463868 0 0 46 1107160 121846 33006 6 93 1 1 0 Note that system CPU usage is very high blocks being written out has dropped by 42%. He analysed this with perf and found perf record -g -a sleep 10 perf report --sort symbol --call-graph fractal,5 34.63% [k] _raw_spin_lock_irqsave | |--97.30%-- isolate_freepages | compaction_alloc | unmap_and_move | migrate_pages | compact_zone | compact_zone_order | try_to_compact_pages | __alloc_pages_direct_compact | __alloc_pages_slowpath | __alloc_pages_nodemask | alloc_pages_vma | do_huge_pmd_anonymous_page | handle_mm_fault | do_page_fault | page_fault | | | |--87.39%-- skb_copy_datagram_iovec | | tcp_recvmsg | | inet_recvmsg | | sock_recvmsg | | sys_recvfrom | | system_call | | __recv | | | | | --100.00%-- (nil) | | | --12.61%-- memcpy --2.70%-- [...] There was other data but primarily it is all showing that compaction is contended heavily on the zone->lock and zone->lru_lock. commit [b2eef8c0: mm: compaction: minimise the time IRQs are disabled while isolating pages for migration] noted that it was possible for migration to hold the lru_lock for an excessive amount of time. Very broadly speaking this patch expands the concept. This patch introduces compact_checklock_irqsave() to check if a lock is contended or the process needs to be scheduled. If either condition is true then async compaction is aborted and the caller is informed. The page allocator will fail a THP allocation if compaction failed due to contention. This patch also introduces compact_trylock_irqsave() which will acquire the lock only if it is not contended and the process does not need to schedule. Reported-by: Jim Schutt Tested-by: Jim Schutt Signed-off-by: Mel Gorman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/compaction: cleanup on compaction_deferred

2012-08-01T01:42:42Z

When CONFIG_COMPACTION is enabled, compaction_deferred() tries to recalculate the deferred limit again, which isn't necessary. When CONFIG_COMPACTION is disabled, compaction_deferred() should return "true" or "false" since it has "bool" for its return value. Signed-off-by: Gavin Shan Acked-by: Minchan Kim Acked-by: Johannes Weiner Acked-by: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Revert "mm: compaction: handle incorrect MIGRATE_UNMOVABLE type pageblocks"

2012-06-04T03:05:57Z

This reverts commit 5ceb9ce6fe9462a298bb2cd5c9f1ca6cb80a0199. That commit seems to be the cause of the mm compation list corruption issues that Dave Jones reported. The locking (or rather, absense there-of) is dubious, as is the use of the 'page' variable once it has been found to be outside the pageblock range. So revert it for now, we can re-visit this for 3.6. If we even need to: as Minchan Kim says, "The patch wasn't a bug fix and even test workload was very theoretical". Reported-and-tested-by: Dave Jones Acked-by: Hugh Dickins Acked-by: KOSAKI Motohiro Acked-by: Minchan Kim Cc: Bartlomiej Zolnierkiewicz Cc: Kyungmin Park Cc: Andrew Morton Signed-off-by: Linus Torvalds

mm: compaction: handle incorrect MIGRATE_UNMOVABLE type pageblocks

2012-05-29T23:22:22Z

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_skipped field to struct compact_control and tracking how many destination pageblocks 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 [minchan@kernel.org: minor cleanups] Cc: Mel Gorman Cc: Minchan Kim Cc: Rik van Riel Cc: Marek Szyprowski Signed-off-by: Bartlomiej Zolnierkiewicz Signed-off-by: Kyungmin Park Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

vmscan: only defer compaction for failed order and higher

2012-03-22T00:54:56Z

Currently a failed order-9 (transparent hugepage) compaction can lead to memory compaction being temporarily disabled for a memory zone. Even if we only need compaction for an order 2 allocation, eg. for jumbo frames networking. The fix is relatively straightforward: keep track of the highest order at which compaction is succeeding, and only defer compaction for orders at which compaction is failing. Signed-off-by: Rik van Riel Cc: Andrea Arcangeli Acked-by: Mel Gorman Cc: Johannes Weiner Cc: Minchan Kim Cc: KOSAKI Motohiro Cc: Hillf Danton Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

vmscan: kswapd carefully call compaction

2012-03-22T00:54:56Z

With CONFIG_COMPACTION enabled, kswapd does not try to free contiguous free pages, even when it is woken for a higher order request. This could be bad for eg. jumbo frame network allocations, which are done from interrupt context and cannot compact memory themselves. Higher than before allocation failure rates in the network receive path have been observed in kernels with compaction enabled. Teach kswapd to defragment the memory zones in a node, but only if required and compaction is not deferred in a zone. [akpm@linux-foundation.org: reduce scope of zones_need_compaction] Signed-off-by: Rik van Riel Acked-by: Mel Gorman Cc: Andrea Arcangeli Cc: Johannes Weiner Cc: Minchan Kim Cc: KOSAKI Motohiro Cc: Hillf Danton Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds