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Sat, 11 Jul 2026 19:03:12 -0700 (PDT) From: Xueyuan Chen To: baolin.wang@linux.alibaba.com Cc: xueyuan.chen21@gmail.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, baohua@kernel.org, zhaonanzhe@xiaomi.com, hannes@cmpxchg.org, 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 Subject: Re: [RFC PATCH v2 3/3] mm/vmscan: avoid pointless large folio splits without swap Date: Sun, 12 Jul 2026 10:03:03 +0800 Message-ID: <20260712020303.326384-1-xueyuan.chen21@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <7ec7533f-e1dc-4236-99cc-6848d651976e@linux.alibaba.com> References: <7ec7533f-e1dc-4236-99cc-6848d651976e@linux.alibaba.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-Transfer-Encoding: 8bit On Fri, Jul 10, 2026 at 03:21:44PM +0800, Baolin Wang wrote: > > >On 7/9/26 10:51 PM, Xueyuan Chen wrote: >> From: "Barry Song (Xiaomi)" >> >> When swap is disabled, exhausted, or unavailable due to memcg swap >> limits, splitting a large anonymous folio cannot make swapout progress. >> The fallback only destroys the large folio and inflates split statistics. >> >> Use -E2BIG from folio_alloc_swap() as the explicit signal that splitting >> the folio might allow swapout of smaller pieces. For other allocation >> failures, keep the existing activation path and avoid the split. >> >> This preserves the split fallback for fragmented or partially available >> swap, while avoiding it when there is no backing space for any part of the >> folio. >> >> Reported-by: Nanzhe Zhao >> Signed-off-by: Barry Song (Xiaomi) >> --- >> mm/vmscan.c | 7 +++++-- >> 1 file changed, 5 insertions(+), 2 deletions(-) >> >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index bd1b1aa12581..40340a88f78e 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -1260,6 +1260,8 @@ static unsigned int shrink_folio_list(struct list_head *folio_list, >> */ >> if (folio_test_anon(folio) && folio_test_swapbacked(folio) && >> !folio_test_swapcache(folio)) { >> + int ret; >> + >> if (!(sc->gfp_mask & __GFP_IO)) >> goto keep_locked; >> if (folio_maybe_dma_pinned(folio)) >> @@ -1278,10 +1280,11 @@ static unsigned int shrink_folio_list(struct list_head *folio_list, >> split_folio_to_list(folio, folio_list)) >> goto activate_locked; >> } >> - if (folio_alloc_swap(folio)) { >> + ret = folio_alloc_swap(folio); >> + if (ret) { >> int __maybe_unused order = folio_order(folio); >> >> - if (!folio_test_large(folio)) >> + if (!folio_test_large(folio) || ret != -E2BIG) >> goto activate_locked_split; > >Like I said in v1 [1], please apply the same change to shmem swap as well. > >[1] >https://lore.kernel.org/all/6e89f868-ca7a-484f-aeea-5d8d029714f2@linux.alibaba.com/ > Hi Baolin, Thanks for pointing this out, and sorry for missing your v1 comment. I'll apply the same folio_alloc_swap() error handling to the shmem swap path in the next version. Thanks, Xueyuan