Re: [PATCH v2] tools/mm: Add thpmaps script to dump THP usage info

[John Hubbard <jhubbard@nvidia.com>]

On 1/10/24 16:11, John Hubbard wrote:
> On 1/10/24 3:21 PM, John Hubbard wrote:
> ...
>> 2) On an mTHP kernel with the latest patchsets (arm64, 64K page size), I
>> *think* I cannot turn off mTHP. I'm still teasing apart how much of this
>> is an instrumentation error, and how much is a measurement problem (with
>> the test suite). And maybe I'm wrong entirely. But the "never" option
>> doesn't seem to have an effect. Unless the latest version of the testsuite
>> is doing something new, sigh.
> 
> OK, it turns out that the test suite changed over to use hugetlbfs
> on this version. So the performance remained high, with or without
> THP settings. heh. Please disregard this part. :)
> 

...although, this does turn out to be informative with respect to
thpmap. Because, look at this case:

Container app does this:

     umount /dev/shm
     mount -t tmpfs tmpfs -o huge=always /dev/shm; findmnt /dev/shm

...and then monitoring it:

# ./thpmaps --cgroup /sys/fs/cgroup  --cont 128K --cont 512K --cont 1M \
             --cont 2M --cont 512M --summary

file-thp-aligned-524288kB:      105906176 kB (97%)
file-thp-partial:                1415680 kB ( 1%)
file-cont-aligned-128kB:        107321600 kB (99%)
file-cont-aligned-512kB:        106886656 kB (98%)
file-cont-aligned-1024kB:       106886144 kB (98%)
file-cont-aligned-2048kB:       106883072 kB (98%)
file-cont-aligned-524288kB:     105906176 kB (97%)

So what I'm trying to say here is, it is still difficult to tell
what's going on. In particular, hugetlbfs vs. [m]THP is not yet clear.


thanks,
-- 
John Hubbard
NVIDIA