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Shutemov" , Roman Gushchin , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH 15/18] mm: memcontrol: make swap tracking an integral part of memory control Message-ID: <20200424030117.GC464082@cmpxchg.org> References: <20200420221126.341272-1-hannes@cmpxchg.org> <20200420221126.341272-16-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200420221126.341272-16-hannes@cmpxchg.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 20, 2020 at 06:11:23PM -0400, Johannes Weiner wrote: > @@ -6884,9 +6876,6 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry) > VM_BUG_ON_PAGE(PageLRU(page), page); > VM_BUG_ON_PAGE(page_count(page), page); > > - if (!do_memsw_account()) > - return; > - > memcg = page->mem_cgroup; > > /* Readahead page, never charged */ I messed up here. mem_cgroup_swapout() must not run on cgroup2, because cgroup2 uses mem_cgroup_try_charge_swap() instead. Both record a swap entry and running them both will trigger a VM_BUG_ON() on an existing record. I'm actually somewhat baffled why this didn't trigger in my MADV_PAGEOUT -> MADV_WILLNEED swap test. memory.max driven swapout triggered it right away. !do_memsw_account() needs to be !cgroup_subsys_on_dfl(memory_cgrp_subsys) > @@ -6913,7 +6902,7 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry) > if (!mem_cgroup_is_root(memcg)) > page_counter_uncharge(&memcg->memory, nr_entries); > > - if (memcg != swap_memcg) { > + if (do_memsw_account() && memcg != swap_memcg) { > if (!mem_cgroup_is_root(swap_memcg)) > page_counter_charge(&swap_memcg->memsw, nr_entries); > page_counter_uncharge(&memcg->memsw, nr_entries); And this can be !cgroup_memory_noswap instead. It'll do the same thing, but will be clearer. I'll have it fixed in version 2.