[Bug corefiles/16981] "AnonHugePages:" is not checked with "Anonymous:"

["sergiodj at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=16981

Sergio Durigan Junior <sergiodj at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sergiodj at redhat dot com

--- Comment #1 from Sergio Durigan Junior <sergiodj at redhat dot com> ---
Size:               8192 kB
Rss:                   0 kB
Pss:                   0 kB
Shared_Clean:          0 kB
Shared_Dirty:          0 kB
Private_Clean:         0 kB
Private_Dirty:         0 kB
Referenced:            0 kB
Anonymous:             0 kB
AnonHugePages:         0 kB
Swap:                  0 kB
KernelPageSize:     2048 kB
MMUPageSize:        2048 kB
Locked:                0 kB
VmFlags: rd wr sh mr mw me ms de ht sd 

I managed to produce the "ht" there.

This whole part of memory management is very confusing.  I am using the program
on <tools/testing/selftests/vm/hugepage-mmap.c>, inside the Linux kernel source
tree, to replicate this.  I also had to modify lots of settings...

First, according to
<https://www.kernel.org/doc/Documentation/vm/hugetlbpage.txt>, one has to check
the value of "HugePages_Total:" on /proc/meminfo.  In my machine, it was 0,
which meant that HugeTLB was never really used.  So the first thing I had to do
was to actually increase this number; I have chosen 20 as a guess (based on the
documentation's example):

  echo 20 > /proc/sys/vm/nr_hugepages

Then, in order to use the .c example mentioned above, I had to mount a
hugetlbfs filesystem:

  mount -t hugetlbfs nodev /home/sergio/mnt

And also give proper permissions to my user:

  chown sergio:sergio /home/sergio/mnt -R

Now, I modified the .c file in order to mmap a file inside this directory.  But
only doing that did not prove enough:

  $ ./a.out 
  mmap: Cannot allocate memory

So, by checking the output of /proc/meminfo again, I saw:

  Hugepagesize:       2048 kB

Since I had added 20 huge pages to the poll, I modified the .c file to mmap
only 8 MB of huge pages (I could have used more memory).  And only then I was
finally able to see the "ht" there.

IMO, all of this investigation ultimately means that we could probably check
for "hg" instead of "ht" in the VmFlags.

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