Re: THP: AnonHugePages in /proc/[pid]/smaps is correct or not?

[Simon Jeons]

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@xxxxxxxxxx  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/