On Sat, Aug 06, 2011 at 06:58:05PM +0200, aarcange@xxxxxxxxxx wrote:
> From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
>
> This adds THP support to mremap (decreases the number of split_huge_page
> called).
>
> Here are also some benchmarks with a proggy like this:
>
> ===
> #define _GNU_SOURCE
> #include <sys/mman.h>
> #include <stdlib.h>
> #include <stdio.h>
> #include <string.h>
> #include <sys/time.h>
>
> #define SIZE (5UL*1024*1024*1024)
>
> int main()
> {
> static struct timeval oldstamp, newstamp;
> long diffsec;
> char *p, *p2, *p3, *p4;
> if (posix_memalign((void **)&p, 2*1024*1024, SIZE))
> perror("memalign"), exit(1);
> if (posix_memalign((void **)&p2, 2*1024*1024, SIZE))
> perror("memalign"), exit(1);
> if (posix_memalign((void **)&p3, 2*1024*1024, 4096))
> perror("memalign"), exit(1);
>
> memset(p, 0xff, SIZE);
> memset(p2, 0xff, SIZE);
> memset(p3, 0x77, 4096);
> gettimeofday(&oldstamp, NULL);
> p4 = mremap(p, SIZE, SIZE, MREMAP_FIXED|MREMAP_MAYMOVE, p3);
> gettimeofday(&newstamp, NULL);
> diffsec = newstamp.tv_sec - oldstamp.tv_sec;
> diffsec = newstamp.tv_usec - oldstamp.tv_usec + 1000000 * diffsec;
> printf("usec %ld\n", diffsec);
> if (p == MAP_FAILED || p4 != p3)
> //if (p == MAP_FAILED)
> perror("mremap"), exit(1);
> if (memcmp(p4, p2, SIZE))
> printf("mremap bug\n"), exit(1);
> printf("ok\n");
>
> return 0;
> }
> ===
>
> THP on
>
> Performance counter stats for './largepage13' (3 runs):
>
> 69195836 dTLB-loads ( +- 3.546% ) (scaled from 50.30%)
> 60708 dTLB-load-misses ( +- 11.776% ) (scaled from 52.62%)
> 676266476 dTLB-stores ( +- 5.654% ) (scaled from 69.54%)
> 29856 dTLB-store-misses ( +- 4.081% ) (scaled from 89.22%)
> 1055848782 iTLB-loads ( +- 4.526% ) (scaled from 80.18%)
> 8689 iTLB-load-misses ( +- 2.987% ) (scaled from 58.20%)
>
> 7.314454164 seconds time elapsed ( +- 0.023% )
>
> THP off
>
> Performance counter stats for './largepage13' (3 runs):
>
> 1967379311 dTLB-loads ( +- 0.506% ) (scaled from 60.59%)
> 9238687 dTLB-load-misses ( +- 22.547% ) (scaled from 61.87%)
> 2014239444 dTLB-stores ( +- 0.692% ) (scaled from 60.40%)
> 3312335 dTLB-store-misses ( +- 7.304% ) (scaled from 67.60%)
> 6764372065 iTLB-loads ( +- 0.925% ) (scaled from 79.00%)
> 8202 iTLB-load-misses ( +- 0.475% ) (scaled from 70.55%)
>
> 9.693655243 seconds time elapsed ( +- 0.069% )
>
> grep thp /proc/vmstat
> thp_fault_alloc 35849
> thp_fault_fallback 0
> thp_collapse_alloc 3
> thp_collapse_alloc_failed 0
> thp_split 0
>
> thp_split 0 confirms no thp split despite plenty of hugepages allocated.
>
> The measurement of only the mremap time (so excluding the 3 long
> memset and final long 10GB memory accessing memcmp):
>
> THP on
>
> usec 14824
> usec 14862
> usec 14859
>
> THP off
>
> usec 256416
> usec 255981
> usec 255847
>
> With an older kernel without the mremap optimizations (the below patch
> optimizes the non THP version too).
>
> THP on
>
> usec 392107
> usec 390237
> usec 404124
>
> THP off
>
> usec 444294
> usec 445237
> usec 445820
>
> I guess with a threaded program that sends more IPI on large SMP it'd
> create an even larger difference.
>
> All debug options are off except DEBUG_VM to avoid skewing the
> results.
>
> The only problem for native 2M mremap like it happens above both the
> source and destination address must be 2M aligned or the hugepmd can't
> be moved without a split but that is an hardware limitation.
>
> Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Acked-by: Johannes Weiner <jweiner@xxxxxxxxxx>
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