On Sat, Jul 20, 2024 at 11:25:28PM +0900, Minwoo Jo wrote:
> This hitshield technique was devised based on the observation that MGLRU
> does not consider the state of the folio when performing eviction.
>
> The assumption is that if a folio that has been updated 1-3 times and not
> frequently updated accumulates generations until it is evicted, it is
> likely to have a low probability of being referenced in the future.
Hi Minwoo. This is interesting work. Thank you for sending it out.
I do not consider myself qualified to comment on your assumption, but
I have some feedback on your implementation.
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index a199c48bc462..053d5620574e 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -189,6 +189,12 @@ struct page {
> void *virtual; /* Kernel virtual address (NULL if
> not kmapped, ie. highmem) */
> #endif /* WANT_PAGE_VIRTUAL */
> + unsigned char hit_shield; /*
> + * The hit_shield variable I added to the page
> + * This variable is responsible for counting
> + * the number of times this
> + * page's generation has been updated.
> + */
We don't really have space in struct page for this kind of thing,
unfortunately. There are a _few_ bits available in page->flags on
64-bit, but even that is a bit tenuous.
