Hi David, On 04/02/2013 06:23 AM, David Rientjes wrote:
On Mon, 1 Apr 2013, Zhouping Liu wrote:Hi all, I found THP can't correctly distinguish one anonymous hugepage map. 1. when /sys/kernel/mm/transparent_hugepage/enabled is 'always', the amount of THP always is one less.It's not a problem with identifying an anonymous mapping as a hugepage, setting thp enabled to "always" does not guarantee that they will always be allocatable or that your mmap() will be 2MB aligned. Your sample code
Both thp and hugetlb pages should be 2MB aligned, correct?
is using mmap() instead of posix_memalign() so you'll probably only get 100% hugepages only 1/512th of the time.2. when /sys/kernel/mm/transparent_hugepage/enabled is 'madvise', THP can't distinguish any one anonymous hugepage size: Testing code: -------- snip -------- unsigned long hugepagesize = (1UL << 21); int main() { void *addr; int i; printf("pid is %d\n", getpid()); for (i = 0; i < 5; i++) { addr = mmap(NULL, hugepagesize, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, -1, 0); if (addr == MAP_FAILED) { perror("mmap"); return -1; } if (madvise(addr, hugepagesize, MADV_HUGEPAGE) == -1) { perror("madvise"); return -1; } memset(addr, i, hugepagesize); } sleep(50); return 0; } --------- snip ---------- The result is that it can't find any AnonHugePages from /proc/[pid]/smaps : -------------- snip ------- 7f0b38cd0000-7f0b396d0000 rw-p 00000000 00:00 0 Size: 10240 kB Rss: 10240 kB Pss: 10240 kB Shared_Clean: 0 kB Shared_Dirty: 0 kB Private_Clean: 0 kB Private_Dirty: 10240 kB Referenced: 10240 kB Anonymous: 10240 kB AnonHugePages: 0 kB Swap: 0 kB KernelPageSize: 4 kB MMUPageSize: 4 kB Locked: 0 kB VmFlags: rd wr mr mw me ac"hg" would be shown in VmFlags if your MADV_HUGEPAGE was successful, are you sure this is the right vma? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
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