Re: [RFC PATCH 3/3] mm: entirely remove lru_add_drain in do_swap_page

[Shakeel Butt <shakeel.butt@linux.dev>]

On Thu, Jun 11, 2026 at 06:51:24PM +0800, Barry Song (Xiaomi) wrote:
> We are doing a lot of redundant lru_add_drain() calls in
> do_swap_page(), especially for synchronous I/O devices. For
> example, the test program below currently ends up draining
> lru_cache 100% of the time:
> 
> int main(int argc, char *argv[])
> {
>         int i;
>  #define SIZE 100*1024*1024
> 	while(1) {
> 		volatile int *p = mmap(0, SIZE, PROT_READ | PROT_WRITE,
>                         MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> 
> 		for (int i = 0; i < SIZE/sizeof(int); i++)
> 			p[i] =  i%64;
> 		madvise((void *)p, SIZE, MADV_PAGEOUT);
> 		for (int i = 0; i < SIZE/sizeof(int); i++)
> 			p[i] =  i%64;
> 		munmap(p, SIZE);
> 	}
> 	return 0;
> }
> 
> Folio reuse now relies primarily on the exclusive hint, making
> lru_cache draining to drop the refcount in lru_cache largely
> irrelevant.
> 
> Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>

Acked-by: Shakeel Butt <shakeel.butt@linux.dev>