Re: [PATCH v2 1/4] mm: avoid unnecessary lru drain for wp_can_reuse_anon_folio()

[Barry Song <baohua@kernel.org>]

On Mon, Jun 29, 2026 at 3:52 PM David Hildenbrand (Arm)
<david@kernel.org> wrote:
[...]
>
> So yeah, if Nadav's reproducer works even without the drain (which I assume), we
> could indeed think about just removing this optimization here.

Yet I think the problem is resolved with the exclusive flag.
Right now, we can still have cases where "exclusive" cannot
address it, such as:

#include <sys/mman.h>

int main(int argc, char *argv[])
{
    int i;
    #define SIZE 30*1024*1024
    while(1) {
        volatile int *p = mmap(0, SIZE, PROT_READ | PROT_WRITE,
             MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
        volatile int q;

        for (int i = 0; i < SIZE/sizeof(int); i++)
              p[i] =  i;
        madvise((void *)p, SIZE, MADV_PAGEOUT);
        if (!fork())
             _exit(0);
        for (int i = 0; i < SIZE/sizeof(int); i++)
              q = p[i];
        for (int i = 0; i < SIZE/sizeof(int); i++)
              p[i] =  i;
        munmap(p, SIZE);
    }
    return 0;
}

I assume this is less frequent and less of a concern?

Thanks
Barry