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| author | Joel Fernandes (Google) <joel@joelfernandes.org> | 2019-01-03 15:28:38 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2019-01-04 13:13:48 -0800 |
| commit | 2c91bd4a4e2e530582d6fd643ea7b86b27907151 (patch) | |
| tree | 4a18cf9d90054666d4ad7e9da673bf7662cacfd6 /arch/Kconfig | |
| parent | 4cf58924951ef80eec636b863e7a53973c44261a (diff) | |
| download | lwn-2c91bd4a4e2e530582d6fd643ea7b86b27907151.tar.gz lwn-2c91bd4a4e2e530582d6fd643ea7b86b27907151.zip | |
mm: speed up mremap by 20x on large regions
Android needs to mremap large regions of memory during memory management
related operations. The mremap system call can be really slow if THP is
not enabled. The bottleneck is move_page_tables, which is copying each
pte at a time, and can be really slow across a large map. Turning on
THP may not be a viable option, and is not for us. This patch speeds up
the performance for non-THP system by copying at the PMD level when
possible.
The speedup is an order of magnitude on x86 (~20x). On a 1GB mremap,
the mremap completion times drops from 3.4-3.6 milliseconds to 144-160
microseconds.
Before:
Total mremap time for 1GB data: 3521942 nanoseconds.
Total mremap time for 1GB data: 3449229 nanoseconds.
Total mremap time for 1GB data: 3488230 nanoseconds.
After:
Total mremap time for 1GB data: 150279 nanoseconds.
Total mremap time for 1GB data: 144665 nanoseconds.
Total mremap time for 1GB data: 158708 nanoseconds.
If THP is enabled the optimization is mostly skipped except in certain
situations.
[joel@joelfernandes.org: fix 'move_normal_pmd' unused function warning]
Link: http://lkml.kernel.org/r/20181108224457.GB209347@google.com
Link: http://lkml.kernel.org/r/20181108181201.88826-3-joelaf@google.com
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Acked-by: Kirill A. Shutemov <kirill@shutemov.name>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Cc: Julia Lawall <Julia.Lawall@lip6.fr>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'arch/Kconfig')
| -rw-r--r-- | arch/Kconfig | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/arch/Kconfig b/arch/Kconfig index e1e540ffa979..b70c952ac838 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -535,6 +535,11 @@ config HAVE_IRQ_TIME_ACCOUNTING Archs need to ensure they use a high enough resolution clock to support irq time accounting and then call enable_sched_clock_irqtime(). +config HAVE_MOVE_PMD + bool + help + Archs that select this are able to move page tables at the PMD level. + config HAVE_ARCH_TRANSPARENT_HUGEPAGE bool |