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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: [PATCH 3/6 v3] mm/page_counter: introduce stock drain APIs Date: Fri, 5 Jun 2026 08:35:59 -0700 Message-ID: <20260605153603.234296-4-joshua.hahnjy@gmail.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260605153603.234296-1-joshua.hahnjy@gmail.com> References: <20260605153603.234296-1-joshua.hahnjy@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 Introduce page_counter variants to replace memcg stock draining functions. page_counter_drain_stock_local() drains the stock of the local CPU, taking a local stock lock to serialize against concurrent charges. page_counter_drain_stock_cpu() does the same, but without taking a local lock. This is possible because it will only be called from the CPU hotplug path, where the CPU is dead and there cannot be any more charges. Suggested-by: Johannes Weiner Signed-off-by: Joshua Hahn --- include/linux/page_counter.h | 3 +++ mm/page_counter.c | 34 ++++++++++++++++++++++++++++++++++ 2 files changed, 37 insertions(+) diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h index c92bb2ee2a581..4a88874019af0 100644 --- a/include/linux/page_counter.h +++ b/include/linux/page_counter.h @@ -111,6 +111,9 @@ static inline void page_counter_reset_watermark(struct page_counter *counter) int page_counter_alloc_stock(struct page_counter *counter, unsigned int batch); void page_counter_disable_stock(struct page_counter *counter); void page_counter_free_stock(struct page_counter *counter); +void page_counter_drain_stock_local(struct page_counter *counter); +void page_counter_drain_stock_cpu(struct page_counter *counter, + unsigned int cpu); #if IS_ENABLED(CONFIG_MEMCG) || IS_ENABLED(CONFIG_CGROUP_DMEM) void page_counter_calculate_protection(struct page_counter *root, diff --git a/mm/page_counter.c b/mm/page_counter.c index 1a71de4f43fd0..7e7eb683472d9 100644 --- a/mm/page_counter.c +++ b/mm/page_counter.c @@ -378,6 +378,40 @@ void page_counter_free_stock(struct page_counter *counter) counter->stock = NULL; } +void page_counter_drain_stock_local(struct page_counter *counter) +{ + struct page_counter_stock *stock; + unsigned long nr_pages; + + if (!counter->stock) + return; + + local_lock(&counter->stock->lock); + stock = this_cpu_ptr(counter->stock); + nr_pages = stock->nr_pages; + stock->nr_pages = 0; + local_unlock(&counter->stock->lock); + + if (nr_pages) + page_counter_uncharge(counter, nr_pages); +} + +void page_counter_drain_stock_cpu(struct page_counter *counter, + unsigned int cpu) +{ + struct page_counter_stock *stock; + unsigned long nr_pages; + + if (!counter->stock) + return; + + stock = per_cpu_ptr(counter->stock, cpu); + nr_pages = stock->nr_pages; + if (nr_pages) { + stock->nr_pages = 0; + page_counter_uncharge(counter, nr_pages); + } +} #if IS_ENABLED(CONFIG_MEMCG) || IS_ENABLED(CONFIG_CGROUP_DMEM) /* -- 2.53.0-Meta