On Wed, Dec 13, 2023 at 08:31:00AM -0800, Yosry Ahmed wrote: > On Wed, Dec 13, 2023 at 8:27 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > > > On Wed, Dec 13, 2023 at 08:24:04AM -0800, Yosry Ahmed wrote: > > > I doubt an extra compound_head() will matter in that path, but if you > > > feel strongly about it that's okay. It's a nice cleanup that's all. > > > > i don't even understand why you think it's a nice cleanup. > > free_pages_prepare() is directly calling __memcg_kmem_uncharge_page() > instead of memcg_kmem_uncharge_page(), and open-coding checks that > already exist in both of them to avoid the unnecessary function call > if possible. I think this should be the job of > memcg_kmem_uncharge_page(), but it's currently missing the > PageMemcgKmem() check (which is in __memcg_kmem_uncharge_page()). > > So I think moving that check to the wrapper allows > free_pages_prepare() to call memcg_kmem_uncharge_page() and without > worrying about those memcg-specific checks. There is a (performance) reason these open coded check are present in page_alloc.c and that is very clear for __memcg_kmem_charge_page() but not so much for __memcg_kmem_uncharge_page(). So, for uncharge path, this seems ok. Now to resolve Willy's concern for the fork() path, I think we can open code the checks there. Willy, any concern with that approach?
