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Fri, 26 Jun 2026 03:01:59 -0700 (PDT) Date: Fri, 26 Jun 2026 06:01:55 -0400 From: Johannes Weiner To: Barry Song Cc: "David Hildenbrand (Arm)" , akpm@linux-foundation.org, axelrasmussen@google.com, baolin.wang@linux.alibaba.com, dev.jain@arm.com, kasong@tencent.com, lance.yang@linux.dev, liam@infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org, npache@redhat.com, qi.zheng@linux.dev, ryan.roberts@arm.com, shakeel.butt@linux.dev, weixugc@google.com, yuanchu@google.com, zhaonanzhe@xiaomi.com, ziy@nvidia.com, Michal Hocko , Roman Gushchin Subject: Re: [RFC PATCH] mm: Avoiding split large folios if swap has no space Message-ID: References: <5790c4a4-d502-4180-82f5-47de5809a4fe@kernel.org> <20260620081017.89085-1-baohua@kernel.org> <4aa8350e-712f-4380-b3bf-2ff06cf2a35d@kernel.org> <3af41c23-2365-4ac1-b1b9-076b6ef7ae9e@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Jun 26, 2026 at 02:15:58PM +0800, Barry Song wrote: > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -5578,7 +5578,7 @@ int __init mem_cgroup_init(void) > * > * Returns 0 on success, -ENOMEM on failure. > */ > -int __mem_cgroup_try_charge_swap(struct folio *folio) > +int __mem_cgroup_try_charge_swap(struct folio *folio, long *left_space) > { > unsigned int nr_pages = folio_nr_pages(folio); > struct swap_cluster_info *ci; > @@ -5611,6 +5611,10 @@ int __mem_cgroup_try_charge_swap(struct folio *folio) > memcg_memory_event(memcg, MEMCG_SWAP_MAX); > memcg_memory_event(memcg, MEMCG_SWAP_FAIL); > mem_cgroup_private_id_put(memcg, nr_pages); > + if (folio_test_large(folio)) > + *left_space = mem_cgroup_get_nr_swap_pages(memcg); It's a bit awkward to walk up the whole hierarchy again when we already have the counter that failed. Please do something like this (not tested!), then use page_counter_margin() against @counter: --- 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 772bac21d155..02472008144f 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5275,12 +5275,9 @@ 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..a0874f853ae0 100644 --- a/mm/page_counter.c +++ b/mm/page_counter.c @@ -46,6 +46,22 @@ static void propagate_protected_usage(struct page_counter *c, } } +/** + * page_counter_margin - remaining usable space within hierarchical limits + * @counter: counter + */ +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