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.
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;
}
memset(addr, i, hugepagesize);
}
sleep(50);
return 0;
}
------ snip ----------
the /proc/[pid]/smaps show that Anonymous is 10240kB but AnonHugePages is 8192Kb, one THP less:
----- snip --------
7f59ccc01000-7f59cd601000 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: 8192 kB
Swap: 0 kB
KernelPageSize: 4 kB
MMUPageSize: 4 kB
Locked: 0 kB
VmFlags: rd wr mr mw me ac hg
------- sinp ---------
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
----------- snip ----------
3. when I made the address aligned with HUGEPAGESIZE using 'posix_memalign()' instead of mmap(),
THP perform good, and can distinguish all anonymous huge pages.
my question is:
1. all the above behaviour is right?
2. why THP can't distinguish one naturally aligned huge page(generated by mmap())?
--
Thanks,
Zhouping
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