linux/mm/compaction.c, branch v4.5

mm/compaction.c: __compact_pgdat() code cleanuup

2016-01-15T00:00:49Z

This patch uses is_via_compact_memory() to distinguish compaction from sysfs or sysctl. And, this patch also reduces indentation on compaction_defer_reset() by filtering these cases first before checking watermark. There is no functional change. Signed-off-by: Joonsoo Kim Acked-by: Yaowei Bai Acked-by: David Rientjes Acked-by: Vlastimil Babka Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/compaction: improve comment for compact_memory tunable knob handler

2016-01-15T00:00:49Z

sysctl_compaction_handler() is the handler function for compact_memory tunable knob under /proc/sys/vm, add the missing knob name to make this more accurate in comment. No functional change. Signed-off-by: Yaowei Bai Acked-by: Vlastimil Babka Acked-by: Michal Nazarewicz Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm, compaction: distinguish contended status in tracepoints

2015-11-06T03:34:48Z

Compaction returns prematurely with COMPACT_PARTIAL when contended or has fatal signal pending. This is ok for the callers, but might be misleading in the traces, as the usual reason to return COMPACT_PARTIAL is that we think the allocation should succeed. After this patch we distinguish the premature ending condition in the mm_compaction_finished and mm_compaction_end tracepoints. The contended status covers the following reasons: - lock contention or need_resched() detected in async compaction - fatal signal pending - too many pages isolated in the zone (only for async compaction) Further distinguishing the exact reason seems unnecessary for now. Signed-off-by: Vlastimil Babka Cc: Joonsoo Kim Cc: Mel Gorman Cc: David Rientjes Cc: Steven Rostedt Cc: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm, compaction: export tracepoints status strings to userspace

2015-11-06T03:34:48Z

Some compaction tracepoints convert the integer return values to strings using the compaction_status_string array. This works for in-kernel printing, but not userspace trace printing of raw captured trace such as via trace-cmd report. This patch converts the private array to appropriate tracepoint macros that result in proper userspace support. trace-cmd output before: transhuge-stres-4235 [000] 453.149280: mm_compaction_finished: node=0 zone=ffffffff81815d7a order=9 ret= after: transhuge-stres-4235 [000] 453.149280: mm_compaction_finished: node=0 zone=ffffffff81815d7a order=9 ret=partial Signed-off-by: Vlastimil Babka Reviewed-by: Steven Rostedt Cc: Joonsoo Kim Cc: Ingo Molnar Cc: Mel Gorman Cc: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/compaction.c: add an is_via_compact_memory() helper

2015-11-06T03:34:48Z

Introduce is_via_compact_memory() helper indicating compacting via /proc/sys/vm/compact_memory to improve readability. To catch this situation in __compaction_suitable, use order as parameter directly instead of using struct compact_control. This patch has no functional changes. Signed-off-by: Yaowei Bai Cc: Mel Gorman Acked-by: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/compaction: correct to flush migrated pages if pageblock skip happens

2015-09-08T22:35:28Z

We cache isolate_start_pfn before entering isolate_migratepages(). If pageblock is skipped in isolate_migratepages() due to whatever reason, cc->migrate_pfn can be far from isolate_start_pfn hence we flush pages that were freed. For example, the following scenario can be possible: - assume order-9 compaction, pageblock order is 9 - start_isolate_pfn is 0x200 - isolate_migratepages() - skip a number of pageblocks - start to isolate from pfn 0x600 - cc->migrate_pfn = 0x620 - return - last_migrated_pfn is set to 0x200 - check flushing condition - current_block_start is set to 0x600 - last_migrated_pfn < current_block_start then do useless flush This wrong flush would not help the performance and success rate so this patch tries to fix it. One simple way to know the exact position where we start to isolate migratable pages is that we cache it in isolate_migratepages() before entering actual isolation. This patch implements that and fixes the problem. Signed-off-by: Joonsoo Kim Acked-by: Vlastimil Babka Cc: Mel Gorman Cc: Rik van Riel Cc: David Rientjes Cc: Minchan Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm, compaction: skip compound pages by order in free scanner

2015-09-08T22:35:28Z

The compaction free scanner is looking for PageBuddy() pages and skipping all others. For large compound pages such as THP or hugetlbfs, we can save a lot of iterations if we skip them at once using their compound_order(). This is generally unsafe and we can read a bogus value of order due to a race, but if we are careful, the only danger is skipping too much. When tested with stress-highalloc from mmtests on 4GB system with 1GB hugetlbfs pages, the vmstat compact_free_scanned count decreased by at least 15%. Signed-off-by: Vlastimil Babka Cc: Minchan Kim Cc: Mel Gorman Acked-by: Joonsoo Kim Acked-by: Michal Nazarewicz Cc: Naoya Horiguchi Cc: Christoph Lameter Cc: Rik van Riel Cc: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm, compaction: always skip all compound pages by order in migrate scanner

2015-09-08T22:35:28Z

The compaction migrate scanner tries to skip THP pages by their order, to reduce number of iterations for pages it cannot isolate. The check is only done if PageLRU() is true, which means it applies to THP pages, but not e.g. hugetlbfs pages or any other non-LRU compound pages, which we have to iterate by base pages. This limitation comes from the assumption that it's only safe to read compound_order() when we have the zone's lru_lock and THP cannot be split under us. But the only danger (after filtering out order values that are not below MAX_ORDER, to prevent overflows) is that we skip too much or too little after reading a bogus compound_order() due to a rare race. This is the same reasoning as patch 99c0fd5e51c4 ("mm, compaction: skip buddy pages by their order in the migrate scanner") introduced for unsafely reading PageBuddy() order. After this patch, all pages are tested for PageCompound() and we skip them by compound_order(). The test is done after the test for balloon_page_movable() as we don't want to assume if balloon pages (or other pages with own isolation and migration implementation if a generic API gets implemented) are compound or not. When tested with stress-highalloc from mmtests on 4GB system with 1GB hugetlbfs pages, the vmstat compact_migrate_scanned count decreased by 15%. [kirill.shutemov@linux.intel.com: change PageTransHuge checks to PageCompound for different series was squashed here] Signed-off-by: Vlastimil Babka Cc: Minchan Kim Acked-by: Mel Gorman Acked-by: Joonsoo Kim Acked-by: Michal Nazarewicz Cc: Naoya Horiguchi Cc: Christoph Lameter Cc: Rik van Riel Cc: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm, compaction: encapsulate resetting cached scanner positions

2015-09-08T22:35:28Z

Reseting the cached compaction scanner positions is now open-coded in __reset_isolation_suitable() and compact_finished(). Encapsulate the functionality in a new function reset_cached_positions(). Signed-off-by: Vlastimil Babka Cc: Minchan Kim Cc: Mel Gorman Cc: Joonsoo Kim Acked-by: Michal Nazarewicz Cc: Naoya Horiguchi Cc: Christoph Lameter Cc: Rik van Riel Cc: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm, compaction: simplify handling restart position in free pages scanner

2015-09-08T22:35:28Z

Handling the position where compaction free scanner should restart (stored in cc->free_pfn) got more complex with commit e14c720efdd7 ("mm, compaction: remember position within pageblock in free pages scanner"). Currently the position is updated in each loop iteration of isolate_freepages(), although it should be enough to update it only when breaking from the loop. There's also an extra check outside the loop updates the position in case we have met the migration scanner. This can be simplified if we move the test for having isolated enough from the for-loop header next to the test for contention, and determining the restart position only in these cases. We can reuse the isolate_start_pfn variable for this instead of setting cc->free_pfn directly. Outside the loop, we can simply set cc->free_pfn to current value of isolate_start_pfn without any extra check. Also add a VM_BUG_ON to catch possible mistake in the future, in case we later add a new condition that terminates isolate_freepages_block() prematurely without also considering the condition in isolate_freepages(). Signed-off-by: Vlastimil Babka Cc: Minchan Kim Acked-by: Mel Gorman Acked-by: Joonsoo Kim Cc: Michal Nazarewicz Cc: Naoya Horiguchi Cc: Christoph Lameter Cc: Rik van Riel Cc: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds