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由 Vlastimil Babka 提交于
The goal of this patch series is to improve performance of munlock() of large mlocked memory areas on systems without THP. This is motivated by reported very long times of crash recovery of processes with such areas, where munlock() can take several seconds. See http://lwn.net/Articles/548108/ The work was driven by a simple benchmark (to be included in mmtests) that mmaps() e.g. 56GB with MAP_LOCKED | MAP_POPULATE and measures the time of munlock(). Profiling was performed by attaching operf --pid to the process and sending a signal to trigger the munlock() part and then notify bach the monitoring wrapper to stop operf, so that only munlock() appears in the profile. The profiles have shown that CPU time is spent mostly by atomic operations and repeated locking per single pages. This series aims to reduce both, starting from simpler to more complex changes. Patch 1 performs a simple cleanup in putback_lru_page() so that page lru base type is not determined without being actually needed. Patch 2 removes an unnecessary call to lru_add_drain() which drains the per-cpu pagevec after each munlocked page is put there. Patch 3 changes munlock_vma_range() to use an on-stack pagevec for isolating multiple non-THP pages under a single lru_lock instead of locking and processing each page separately. Patch 4 changes the NR_MLOCK accounting to be called only once per the pvec introduced by previous patch. Patch 5 uses the introduced pagevec to batch also the work of putback_lru_page when possible, bypassing the per-cpu pvec and associated overhead. Patch 6 removes a redundant get_page/put_page pair which saves costly atomic operations. Patch 7 avoids calling follow_page_mask() on each individual page, and obtains multiple page references under a single page table lock where possible. Measurements were made using 3.11-rc3 as a baseline. The first set of measurements shows the possibly ideal conditions where batching should help the most. All memory is allocated from a single NUMA node and THP is disabled. timedmunlock 3.11-rc3 3.11-rc3 3.11-rc3 3.11-rc3 3.11-rc3 3.11-rc3 3.11-rc3 3.11-rc3 0 1 2 3 4 5 6 7 Elapsed min 3.38 ( 0.00%) 3.39 ( -0.13%) 3.00 ( 11.33%) 2.70 ( 20.20%) 2.67 ( 21.11%) 2.37 ( 29.88%) 2.20 ( 34.91%) 1.91 ( 43.59%) Elapsed mean 3.39 ( 0.00%) 3.40 ( -0.23%) 3.01 ( 11.33%) 2.70 ( 20.26%) 2.67 ( 21.21%) 2.38 ( 29.88%) 2.21 ( 34.93%) 1.92 ( 43.46%) Elapsed stddev 0.01 ( 0.00%) 0.01 (-43.09%) 0.01 ( 15.42%) 0.01 ( 23.42%) 0.00 ( 89.78%) 0.01 ( -7.15%) 0.00 ( 76.69%) 0.02 (-91.77%) Elapsed max 3.41 ( 0.00%) 3.43 ( -0.52%) 3.03 ( 11.29%) 2.72 ( 20.16%) 2.67 ( 21.63%) 2.40 ( 29.50%) 2.21 ( 35.21%) 1.96 ( 42.39%) Elapsed range 0.03 ( 0.00%) 0.04 (-51.16%) 0.02 ( 6.27%) 0.02 ( 14.67%) 0.00 ( 88.90%) 0.03 (-19.18%) 0.01 ( 73.70%) 0.06 (-113.35% The second set of measurements simulates the worst possible conditions for batching by using numactl --interleave, so that there is in fact only one page per pagevec. Even in this case the series seems to improve performance thanks to reduced atomic operations and removal of lru_add_drain(). timedmunlock 3.11-rc3 3.11-rc3 3.11-rc3 3.11-rc3 3.11-rc3 3.11-rc3 3.11-rc3 3.11-rc3 0 1 2 3 4 5 6 7 Elapsed min 4.00 ( 0.00%) 4.04 ( -0.93%) 3.87 ( 3.37%) 3.72 ( 6.94%) 3.81 ( 4.72%) 3.69 ( 7.82%) 3.64 ( 8.92%) 3.41 ( 14.81%) Elapsed mean 4.17 ( 0.00%) 4.15 ( 0.51%) 4.03 ( 3.49%) 3.89 ( 6.84%) 3.86 ( 7.48%) 3.89 ( 6.69%) 3.70 ( 11.27%) 3.48 ( 16.59%) Elapsed stddev 0.16 ( 0.00%) 0.08 ( 50.76%) 0.10 ( 41.58%) 0.16 ( 4.59%) 0.05 ( 72.38%) 0.19 (-12.91%) 0.05 ( 68.09%) 0.06 ( 66.03%) Elapsed max 4.34 ( 0.00%) 4.32 ( 0.56%) 4.19 ( 3.62%) 4.12 ( 5.15%) 3.91 ( 9.88%) 4.12 ( 5.25%) 3.80 ( 12.58%) 3.56 ( 18.08%) Elapsed range 0.34 ( 0.00%) 0.28 ( 17.91%) 0.32 ( 6.45%) 0.40 (-15.73%) 0.10 ( 70.06%) 0.43 (-24.84%) 0.15 ( 55.32%) 0.15 ( 56.16%) For completeness, a third set of measurements shows the situation where THP is enabled and allocations are again done on a single NUMA node. Here munlock() is already very fast thanks to huge pages, and this series does not compromise that performance. It seems that the removal of call to lru_add_drain() still helps a bit. timedmunlock 3.11-rc3 3.11-rc3 3.11-rc3 3.11-rc3 3.11-rc3 3.11-rc3 3.11-rc3 3.11-rc3 0 1 2 3 4 5 6 7 Elapsed min 0.01 ( 0.00%) 0.01 ( -0.11%) 0.01 ( 6.59%) 0.01 ( 5.41%) 0.01 ( 5.45%) 0.01 ( 5.03%) 0.01 ( 6.08%) 0.01 ( 5.20%) Elapsed mean 0.01 ( 0.00%) 0.01 ( -0.27%) 0.01 ( 6.39%) 0.01 ( 5.30%) 0.01 ( 5.32%) 0.01 ( 5.03%) 0.01 ( 5.97%) 0.01 ( 5.22%) Elapsed stddev 0.00 ( 0.00%) 0.00 ( -9.59%) 0.00 ( 10.77%) 0.00 ( 3.24%) 0.00 ( 24.42%) 0.00 ( 31.86%) 0.00 ( -7.46%) 0.00 ( 6.11%) Elapsed max 0.01 ( 0.00%) 0.01 ( -0.01%) 0.01 ( 6.83%) 0.01 ( 5.42%) 0.01 ( 5.79%) 0.01 ( 5.53%) 0.01 ( 6.08%) 0.01 ( 5.26%) Elapsed range 0.00 ( 0.00%) 0.00 ( 7.30%) 0.00 ( 24.38%) 0.00 ( 6.10%) 0.00 ( 30.79%) 0.00 ( 42.52%) 0.00 ( 6.11%) 0.00 ( 10.07%) This patch (of 7): In putback_lru_page() since commit c53954a0 (""mm: remove lru parameter from __lru_cache_add and lru_cache_add_lru") it is no longer needed to determine lru list via page_lru_base_type(). This patch replaces it with simple flag is_unevictable which says that the page was put on the inevictable list. This is the only information that matters in subsequent tests. Signed-off-by: NVlastimil Babka <vbabka@suse.cz> Reviewed-by: NJörn Engel <joern@logfs.org> Acked-by: NMel Gorman <mgorman@suse.de> Cc: Michel Lespinasse <walken@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@suse.cz> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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