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SubjectRe: [PATCH 4/4] mm: migrate: Batch TLB flushing when unmapping pages for migration
On Thu, Apr 16, 2015 at 11:22:46AM +0100, Mel Gorman wrote:
> Page reclaim batches multiple TLB flushes into one IPI and this patch teaches
> page migration to also batch any necessary flushes. MMtests has a THP scale
> microbenchmark that deliberately fragments memory and then allocates THPs
> to stress compaction. It's not a page reclaim benchmark and recent kernels
> avoid excessive compaction but this patch reduced system CPU usage
>
> 4.0.0 4.0.0
> baseline batchmigrate-v1
> User 970.70 1012.24
> System 2067.48 1840.00
> Elapsed 1520.63 1529.66
>
> Note that this particular workload was not TLB flush intensive with peaks
> in interrupts during the compaction phase. The 4.0 kernel peaked at 345K
> interrupts/second, the kernel that batches reclaim TLB entries peaked at
> 13K interrupts/second and this patch peaked at 10K interrupts/second.
>
> Signed-off-by: Mel Gorman <mgorman@suse.de>

The following is needed on !x86 although it's pointless to test on !x86
at the moment.

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 361bf59e0594..548c94834112 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2784,10 +2784,6 @@ void alloc_tlb_ubc(void)
cpumask_clear(&current->tlb_ubc->cpumask);
current->tlb_ubc->nr_pages = 0;
}
-#else
-static inline void alloc_tlb_ubc(void)
-{
-}
#endif /* CONFIG_ARCH_SUPPORTS_LOCAL_TLB_PFN_FLUSH */

unsigned long try_to_free_pages(struct zonelist *zonelist, int order,

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