Re: [REGRESSION] mm/mprotect: 2x+ slowdown for >=400KiB regions since PTE batching (cac1db8c3aad)

["David Hildenbrand (Arm)" <david@kernel.org>]

> int main(int argc, char **argv)
> {
>     int i, j, ret;
>     long long k;
> 
>     if (argc < 4) {
>         printf("USAGE: %s region_size_kib region_count iterations\n", argv[0]);
>         printf("Creates multiple regions and times mprotect() calls\n");
>         return 1;
>     }
> 
>     long region_size = atol(argv[1]) * 1024L;
>     int region_count = atoi(argv[2]);
>     int iterations = atoi(argv[3]);
> 
>     int pagesize = sysconf(_SC_PAGESIZE);
> 
>     vchar_t **regions = malloc(region_count * sizeof(vchar_t*));
>     if (!regions) {
>         perror("malloc");
>         return 1;
>     }
> 
>     for (i = 0; i < region_count; i++) {
>         regions[i] = (vchar_t *) mmap(NULL, region_size,
>                       PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0L);
> 

I assume that the regression might be more pronounced with MAP_SHARED, 
because there we really didn't ever required the page/folio during 
mprotect() IIRC.

-- 
Cheers,

David