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Wed, 29 Jul 2026 19:17:05 -0700 (PDT) Received: from debian.lan ([155.117.85.23]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-84e9fe23143sm2159628b3a.2.2026.07.29.19.16.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Jul 2026 19:17:05 -0700 (PDT) From: Xueyuan Chen To: akpm@linux-foundation.org, linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, zhaonanzhe@xiaomi.com, baohua@kernel.org, hannes@cmpxchg.org, youngjun.park@lge.com, baolin.wang@linux.alibaba.com, hughd@google.com, chrisl@kernel.org, kasong@tencent.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, baoquan.he@linux.dev, mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, 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, Xueyuan Chen Subject: [RFC PATCH v4 1/4] mm: add page_counter_margin() Date: Thu, 30 Jul 2026 10:16:27 +0800 Message-ID: <20260730021630.2235914-2-xueyuan.chen21@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260730021630.2235914-1-xueyuan.chen21@gmail.com> References: <20260730021630.2235914-1-xueyuan.chen21@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Johannes Weiner mem_cgroup_get_nr_swap_pages() open-codes the remaining capacity across the memcg swap counter hierarchy. Add page_counter_margin() to return the minimum usable space from a page counter to the root, and use it in mem_cgroup_get_nr_swap_pages(). This is a pure refactoring with no intended behavior change. Signed-off-by: Johannes Weiner Signed-off-by: Xueyuan Chen --- include/linux/page_counter.h | 1 + mm/memcontrol.c | 9 +++------ mm/page_counter.c | 20 ++++++++++++++++++++ 3 files changed, 24 insertions(+), 6 deletions(-) diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h index d649b6bbbc87..07b7cb12249c 100644 --- a/include/linux/page_counter.h +++ b/include/linux/page_counter.h @@ -68,6 +68,7 @@ static inline unsigned long page_counter_read(struct page_counter *counter) return atomic_long_read(&counter->usage); } +long page_counter_margin(struct page_counter *counter); void page_counter_cancel(struct page_counter *counter, unsigned long nr_pages); void page_counter_charge(struct page_counter *counter, unsigned long nr_pages); bool page_counter_try_charge(struct page_counter *counter, diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 8319ad8c5c23..109c08be91cf 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5670,12 +5670,9 @@ long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg) { long nr_swap_pages = get_nr_swap_pages(); - if (mem_cgroup_disabled() || do_memsw_account()) - return nr_swap_pages; - for (; !mem_cgroup_is_root(memcg); memcg = parent_mem_cgroup(memcg)) - nr_swap_pages = min_t(long, nr_swap_pages, - READ_ONCE(memcg->swap.max) - - page_counter_read(&memcg->swap)); + if (!mem_cgroup_disabled() && !do_memsw_account()) + nr_swap_pages = min(nr_swap_pages, page_counter_margin(&memcg->swap)); + return nr_swap_pages; } diff --git a/mm/page_counter.c b/mm/page_counter.c index 661e0f2a5127..450543f4b318 100644 --- a/mm/page_counter.c +++ b/mm/page_counter.c @@ -46,6 +46,26 @@ static void propagate_protected_usage(struct page_counter *c, } } +/** + * page_counter_margin - remaining usable space within hierarchical limits + * @counter: counter + * + * Return: The minimum value of max minus usage across @counter and all of + * its ancestors. The value may be negative during a concurrent charge. + */ +long page_counter_margin(struct page_counter *counter) +{ + long margin = PAGE_COUNTER_MAX; + + do { + long m = READ_ONCE(counter->max) - page_counter_read(counter); + + margin = min(margin, m); + } while ((counter = counter->parent)); + + return margin; +} + /** * page_counter_cancel - take pages out of the local counter * @counter: counter -- 2.47.3