On Thu, Dec 7, 2023 at 11:24 AM Nhat Pham <nphamcs@xxxxxxxxx> wrote: > > During our experiment with zswap, we sometimes observe swap IOs due to > occasional zswap store failures and writebacks-to-swap. These swapping > IOs prevent many users who cannot tolerate swapping from adopting zswap > to save memory and improve performance where possible. > > This patch adds the option to disable this behavior entirely: do not > writeback to backing swapping device when a zswap store attempt fail, > and do not write pages in the zswap pool back to the backing swap > device (both when the pool is full, and when the new zswap shrinker is > called). > > This new behavior can be opted-in/out on a per-cgroup basis via a new > cgroup file. By default, writebacks to swap device is enabled, which is > the previous behavior. Initially, writeback is enabled for the root > cgroup, and a newly created cgroup will inherit the current setting of > its parent. > > Note that this is subtly different from setting memory.swap.max to 0, as > it still allows for pages to be stored in the zswap pool (which itself > consumes swap space in its current form). > > This patch should be applied on top of the zswap shrinker series: > > https://lore.kernel.org/linux-mm/20231130194023.4102148-1-nphamcs@xxxxxxxxx/ > > as it also disables the zswap shrinker, a major source of zswap > writebacks. > > Suggested-by: Johannes Weiner <hannes@xxxxxxxxxxx> > Signed-off-by: Nhat Pham <nphamcs@xxxxxxxxx> > Reviewed-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx> FTR I still prefer a more generic and future-proof interface (e.g. memory.swap.tiers), but I am not opposed to this. It will just be annoying to have different interfaces with overlapping functionalities in the future if/when the need for a generic interface arises.
