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* mm: compaction: prevent kswapd compacting memory to reduce CPU usageAndrea Arcangeli2011-03-221-7/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 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 <aarcange@redhat.com> Signed-off-by: Mel Gorman <mel@csn.ul.ie> Reported-by: Arthur Marsh <arthur.marsh@internode.on.net> Tested-by: Arthur Marsh <arthur.marsh@internode.on.net> Cc: <stable@kernel.org> [2.6.38.1] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* thp: use compaction in kswapd for GFP_ATOMIC order > 0Andrea Arcangeli2011-01-131-3/+8
| | | | | | | | | | This takes advantage of memory compaction to properly generate pages of order > 0 if regular page reclaim fails and priority level becomes more severe and we don't reach the proper watermarks. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm: migration: allow migration to operate asynchronously and avoid ↵Mel Gorman2011-01-131-4/+6
| | | | | | | | | | | | | | | | | | | | | | | | | synchronous compaction in the faster path Migration synchronously waits for writeback if the initial passes fails. Callers of memory compaction do not necessarily want this behaviour if the caller is latency sensitive or expects that synchronous migration is not going to have a significantly better success rate. This patch adds a sync parameter to migrate_pages() allowing the caller to indicate if wait_on_page_writeback() is allowed within migration or not. For reclaim/compaction, try_to_compact_pages() is first called asynchronously, direct reclaim runs and then try_to_compact_pages() is called synchronously as there is a greater expectation that it'll succeed. [akpm@linux-foundation.org: build/merge fix] Signed-off-by: Mel Gorman <mel@csn.ul.ie> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Rik van Riel <riel@redhat.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Cc: Andy Whitcroft <apw@shadowen.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm: vmscan: reclaim order-0 and use compaction instead of lumpy reclaimMel Gorman2011-01-131-0/+14
| | | | | | | | | | | | | | | | | | | | | | | | | | Lumpy reclaim is disruptive. It reclaims a large number of pages and ignores the age of the pages it reclaims. This can incur significant stalls and potentially increase the number of major faults. Compaction has reached the point where it is considered reasonably stable (meaning it has passed a lot of testing) and is a potential candidate for displacing lumpy reclaim. This patch introduces an alternative to lumpy reclaim whe compaction is available called reclaim/compaction. The basic operation is very simple - instead of selecting a contiguous range of pages to reclaim, a number of order-0 pages are reclaimed and then compaction is later by either kswapd (compact_zone_order()) or direct compaction (__alloc_pages_direct_compact()). [akpm@linux-foundation.org: fix build] [akpm@linux-foundation.org: use conventional task_struct naming] Signed-off-by: Mel Gorman <mel@csn.ul.ie> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Rik van Riel <riel@redhat.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Cc: Andy Whitcroft <apw@shadowen.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm: compaction: defer compaction using an exponential backoff when ↵Mel Gorman2010-05-251-0/+39
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | compaction fails The fragmentation index may indicate that a failure is due to external fragmentation but after a compaction run completes, it is still possible for an allocation to fail. There are two obvious reasons as to why o Page migration cannot move all pages so fragmentation remains o A suitable page may exist but watermarks are not met In the event of compaction followed by an allocation failure, this patch defers further compaction in the zone (1 << compact_defer_shift) times. If the next compaction attempt also fails, compact_defer_shift is increased up to a maximum of 6. If compaction succeeds, the defer counters are reset again. The zone that is deferred is the first zone in the zonelist - i.e. the preferred zone. To defer compaction in the other zones, the information would need to be stored in the zonelist or implemented similar to the zonelist_cache. This would impact the fast-paths and is not justified at this time. Signed-off-by: Mel Gorman <mel@csn.ul.ie> Cc: Rik van Riel <riel@redhat.com> Cc: Minchan Kim <minchan.kim@gmail.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Christoph Lameter <cl@linux-foundation.org> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm: compaction: add a tunable that decides when memory should be compacted ↵Mel Gorman2010-05-251-0/+3
| | | | | | | | | | | | | | | | | | | | | | | and when it should be reclaimed The kernel applies some heuristics when deciding if memory should be compacted or reclaimed to satisfy a high-order allocation. One of these is based on the fragmentation. If the index is below 500, memory will not be compacted. This choice is arbitrary and not based on data. To help optimise the system and set a sensible default for this value, this patch adds a sysctl extfrag_threshold. The kernel will only compact memory if the fragmentation index is above the extfrag_threshold. [randy.dunlap@oracle.com: Fix build errors when proc fs is not configured] Signed-off-by: Mel Gorman <mel@csn.ul.ie> Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com> Cc: Rik van Riel <riel@redhat.com> Cc: Minchan Kim <minchan.kim@gmail.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Christoph Lameter <cl@linux-foundation.org> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm: compaction: direct compact when a high-order allocation failsMel Gorman2010-05-251-4/+20
| | | | | | | | | | | | | | | | | | | | | | | | | | | Ordinarily when a high-order allocation fails, direct reclaim is entered to free pages to satisfy the allocation. With this patch, it is determined if an allocation failed due to external fragmentation instead of low memory and if so, the calling process will compact until a suitable page is freed. Compaction by moving pages in memory is considerably cheaper than paging out to disk and works where there are locked pages or no swap. If compaction fails to free a page of a suitable size, then reclaim will still occur. Direct compaction returns as soon as possible. As each block is compacted, it is checked if a suitable page has been freed and if so, it returns. [akpm@linux-foundation.org: Fix build errors] [aarcange@redhat.com: fix count_vm_event preempt in memory compaction direct reclaim] Signed-off-by: Mel Gorman <mel@csn.ul.ie> Acked-by: Rik van Riel <riel@redhat.com> Reviewed-by: Minchan Kim <minchan.kim@gmail.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Christoph Lameter <cl@linux-foundation.org> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm: compaction: add /sys trigger for per-node memory compactionMel Gorman2010-05-251-0/+16
| | | | | | | | | | | | | | | | | Add a per-node sysfs file called compact. When the file is written to, each zone in that node is compacted. The intention that this would be used by something like a job scheduler in a batch system before a job starts so that the job can allocate the maximum number of hugepages without significant start-up cost. Signed-off-by: Mel Gorman <mel@csn.ul.ie> Acked-by: Rik van Riel <riel@redhat.com> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Reviewed-by: Christoph Lameter <cl@linux-foundation.org> Reviewed-by: Minchan Kim <minchan.kim@gmail.com> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm: compaction: add /proc trigger for memory compactionMel Gorman2010-05-251-0/+6
| | | | | | | | | | | | | | | | Add a proc file /proc/sys/vm/compact_memory. When an arbitrary value is written to the file, all zones are compacted. The expected user of such a trigger is a job scheduler that prepares the system before the target application runs. Signed-off-by: Mel Gorman <mel@csn.ul.ie> Acked-by: Rik van Riel <riel@redhat.com> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Reviewed-by: Minchan Kim <minchan.kim@gmail.com> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Reviewed-by: Christoph Lameter <cl@linux-foundation.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm: compaction: memory compaction coreMel Gorman2010-05-251-0/+9
This patch is the core of a mechanism which compacts memory in a zone by relocating movable pages towards the end of the zone. A single compaction run involves a migration scanner and a free scanner. Both scanners operate on pageblock-sized areas in the zone. The migration scanner starts at the bottom of the zone and searches for all movable pages within each area, isolating them onto a private list called migratelist. The free scanner starts at the top of the zone and searches for suitable areas and consumes the free pages within making them available for the migration scanner. The pages isolated for migration are then migrated to the newly isolated free pages. [aarcange@redhat.com: Fix unsafe optimisation] [mel@csn.ul.ie: do not schedule work on other CPUs for compaction] Signed-off-by: Mel Gorman <mel@csn.ul.ie> Acked-by: Rik van Riel <riel@redhat.com> Reviewed-by: Minchan Kim <minchan.kim@gmail.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Christoph Lameter <cl@linux-foundation.org> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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