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Tue, 21 Jul 2026 04:53:34 -0700 (PDT) Date: Tue, 21 Jul 2026 07:53:33 -0400 From: Johannes Weiner To: Barry Song Cc: Xueyuan Chen , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, zhaonanzhe@xiaomi.com, mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, chrisl@kernel.org, kasong@tencent.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, youngjun.park@lge.com, david@kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, qi.zheng@linux.dev, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, baolin.wang@linux.alibaba.com, hughd@google.com Subject: Re: [RFC PATCH v3 2/4] mm: distinguish large folio swap allocation failures Message-ID: References: <20260717122514.51514-1-xueyuan.chen21@gmail.com> <20260717122514.51514-3-xueyuan.chen21@gmail.com> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue, Jul 21, 2026 at 04:15:13PM +0800, Barry Song wrote: > On Fri, Jul 17, 2026 at 8:25 PM Xueyuan Chen wrote: > > @@ -5495,6 +5497,9 @@ int __mem_cgroup_try_charge_swap(struct folio *folio, swp_entry_t entry) > > rcu_read_lock(); > > memcg = obj_cgroup_memcg(objcg); > > if (!entry.val) { > > + if (nr_swap_pages && !mem_cgroup_is_root(memcg)) > > + *nr_swap_pages = min(*nr_swap_pages, > > + page_counter_margin(&memcg->swap)); > > This looks a bit odd. Could we decouple *nr_swap_pages from margin and > have the function always return margin instead? > > I don't think this function needs to care about the initial value returned by > get_nr_swap_pages(). While folio_alloc_swap() may depend on it, they're > different software layers, and we shouldn't couple them together. Agreed!