On Mon, Sep 25, 2023 at 01:17:04PM -0700, Yosry Ahmed wrote: > +Chris Li > > On Tue, Sep 19, 2023 at 10:14 AM Nhat Pham <nphamcs@xxxxxxxxx> wrote: > > > > From: Domenico Cerasuolo <cerasuolodomenico@xxxxxxxxx> > > > > Currently, we only have a single global LRU for zswap. This makes it > > impossible to perform worload-specific shrinking - an memcg cannot > > determine which pages in the pool it owns, and often ends up writing > > pages from other memcgs. This issue has been previously observed in > > practice and mitigated by simply disabling memcg-initiated shrinking: > > > > https://lore.kernel.org/all/20230530232435.3097106-1-nphamcs@xxxxxxxxx/T/#u > > > > This patch fully resolves the issue by replacing the global zswap LRU > > with memcg- and NUMA-specific LRUs, and modify the reclaim logic: > > > > a) When a store attempt hits an memcg limit, it now triggers a > > synchronous reclaim attempt that, if successful, allows the new > > hotter page to be accepted by zswap. > > b) If the store attempt instead hits the global zswap limit, it will > > trigger an asynchronous reclaim attempt, in which an memcg is > > selected for reclaim in a round-robin-like fashion. > > Hey Nhat, > > I didn't take a very close look as I am currently swamped, but going > through the patch I have some comments/questions below. > > I am not very familiar with list_lru, but it seems like the existing > API derives the node and memcg from the list item itself. Seems like > we can avoid a lot of changes if we allocate struct zswap_entry from > the same node as the page, and account it to the same memcg. Would > this be too much of a change or too strong of a restriction? It's a > slab allocation and we will free memory on that node/memcg right > after. My 2c, but I kind of hate that assumption made by list_lru. We ran into problems with it with the THP shrinker as well. That one strings up 'struct page', and virt_to_page(page) results in really fun to debug issues. IMO it would be less error prone to have memcg and nid as part of the regular list_lru_add() function signature. And then have an explicit list_lru_add_obj() that does a documented memcg lookup. Because of the overhead, we've been selective about the memory we charge. I'd hesitate to do it just to work around list_lru.
