On Fri, Jan 26, 2024 at 12:31 AM <chengming.zhou@xxxxxxxxx> wrote:
>
> From: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
>
> LRU_SKIP can only be returned if we don't ever dropped lru lock, or
> we need to return LRU_RETRY to restart from the head of lru list.
Ooops. You're right! I just double checked and only LRU_REMOVED_RETRY
and LRU_RETRY indicate we might have dropped the lock. My bad.
>
> Actually we may need to introduce another LRU_STOP to really terminate
> the ongoing shrinking scan process, when we encounter a warm page
Yup. This is what I was trying (and failing) to do. To be honest, this
needs to be even stronger: short-circuit ALL concurrent/ongoing zswap
shrinker scan processes that are touching this memcg (as they will
also shrink into warmer regions going forward). But that's a bit more
engineering to do. LRU_STOP, which stops this scan process, would be a
good place to start.
> already in the swap cache. The current list_lru implementation
> doesn't have this function to early break from __list_lru_walk_one.
>
> Fixes: b5ba474f3f51 ("zswap: shrink zswap pool based on memory pressure")
> Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Reviewed-by: Nhat Pham <nphamcs@xxxxxxxxx>
> ---
> mm/zswap.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 00e90b9b5417..81cb3790e0dd 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -901,10 +901,8 @@ static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_o
> * into the warmer region. We should terminate shrinking (if we're in the dynamic
> * shrinker context).
> */
> - if (writeback_result == -EEXIST && encountered_page_in_swapcache) {
> - ret = LRU_SKIP;
> + if (writeback_result == -EEXIST && encountered_page_in_swapcache)
> *encountered_page_in_swapcache = true;
> - }
>
> goto put_unlock;
> }
> --
> 2.40.1
>
