On Sat, Jun 19, 2021 at 02:20:02AM -0700, Peter Collingbourne wrote:
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <sys/mman.h>
> #include <unistd.h>
>
> constexpr unsigned char pattern_byte = 0xaa;
>
> #define PAGE_SIZE 4096
>
> _Alignas(PAGE_SIZE) static unsigned char pattern[PAGE_SIZE];
>
> int main(int argc, char **argv) {
> if (argc < 3)
> return 1;
> bool use_refpage = argc > 3;
> size_t mmap_size = atoi(argv[1]);
> size_t touch_size = atoi(argv[2]);
>
> int refpage_fd;
> if (use_refpage) {
> memset(pattern, pattern_byte, PAGE_SIZE);
> refpage_fd = syscall(448, pattern, 0);
> }
> for (unsigned i = 0; i != 1000; ++i) {
> char *p;
> if (use_refpage) {
> p = (char *)mmap(0, mmap_size, PROT_READ | PROT_WRITE, MAP_PRIVATE,
> refpage_fd, 0);
> } else {
> p = (char *)mmap(0, mmap_size, PROT_READ | PROT_WRITE,
> MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> memset(p, pattern_byte, mmap_size);
> }
> for (unsigned j = 0; j < touch_size; j += PAGE_SIZE)
> p[j] = 0;
> munmap(p, mmap_size);
> }
> }
I don't like the inteface. It is tied to PAGE_SIZE and this doesn't seem
to be very future looking. How would it work with THPs?
Maybe we should cosider passing down a filling pattern to kernel and let
kernel allocate appropriate page size on read page fault? The pattern has
to be power of 2 and limited in lenght.
--
Kirill A. Shutemov
