On 18.11.24 15:13, Avi Kivity wrote:
#define _GNU_SOURCE
#include <sys/mman.h>
#include <linux/memfd.h>
#include <unistd.h>
#include <stddef.h>
int main(int ac, char** av) {
size_t memsz = (size_t)2048 << 20;
int fd = memfd_create("memory", MFD_CLOEXEC);
ftruncate(fd, memsz);
void* p = mmap((void*)0x40000000, memsz, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FILE, fd, 0);
madvise(p, memsz, MADV_HUGEPAGE);
madvise(p, memsz, MADV_POPULATE_WRITE);
madvise(p, memsz, MADV_COLLAPSE);
pause();
return 0;
}
Hi,
While memfd is documented as using anonymous pages, AnonHugePages shows
as zero.
it's an anonymous file, not anonymous memory. memfd is shmem in diguise.
If memfd incompatible with transparent hugepages?
Shmem supports THP.
But you have one flaws in your program: you have to mmap it MAP_SHARED.
It's shmem.
Otherwise during MADV_POPULATE_WRITE you're simply allocating a shmem
page (pageache), and the COW it to map an anonymous page in your page
tables, resulting in a double memory consumption (pagecache+anonymous
memory). khugepaged does currently not operate on such VMAs.
If you use MAP_SHARED in your example above:
$ cat /proc/`pgrep tst`/smaps_rollup
00400000-7ffc2770d000 ---p 00000000 00:00 0
[rollup]
Rss: 2098460 kB
Pss: 2097269 kB
Pss_Dirty: 2097248 kB
Pss_Anon: 96 kB
Pss_File: 21 kB
Pss_Shmem: 2097152 kB
Shared_Clean: 1200 kB
Shared_Dirty: 0 kB
Private_Clean: 12 kB
Private_Dirty: 2097248 kB
Referenced: 2098460 kB
Anonymous: 96 kB
KSM: 0 kB
LazyFree: 0 kB
AnonHugePages: 0 kB
ShmemPmdMapped: 2097152 kB
FilePmdMapped: 0 kB
Shared_Hugetlb: 0 kB
Private_Hugetlb: 0 kB
Swap: 0 kB
SwapPss: 0 kB
Locked: 0 kB
--
Cheers,
David / dhildenb
