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Received: from 30.74.144.127(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0XAaJnml_1788840106 cluster:ay36) by smtp.aliyun-inc.com; Tue, 08 Sep 2026 12:01:47 +0800 Message-ID: <31494361-406e-4874-8a2c-2c6f5cee5321@linux.alibaba.com> Date: Tue, 8 Sep 2026 12:01:46 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: mglru: clear the reference counter for rejected folios From: Baolin Wang To: Barry Song , Baoquan He Cc: akpm@linux-foundation.org, kasong@tencent.com, qi.zheng@linux.dev, shakeel.butt@linux.dev, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, hannes@cmpxchg.org, david@kernel.org, mhocko@kernel.org, ljs@kernel.org, ridong.chen@linux.dev, hebaoquan@kylinos.cn, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <8e4db9a298c5ea6ccb192e274caed5b96f0cf022.1788751143.git.baolin.wang@linux.alibaba.com> <67d9bbcf-2991-4867-8afb-14bad1cebf8d@linux.alibaba.com> In-Reply-To: <67d9bbcf-2991-4867-8afb-14bad1cebf8d@linux.alibaba.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 66C5940008 X-Stat-Signature: y1j8bohnah8rs5bt5ribsy3qjuf3gazc X-HE-Tag: 1788840111-517632 X-HE-Meta: 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 j7F3EhQm 2GlOPUJjfCqFq+0Ye0HnO8/kcaH0PLUhQnZCRDpwIzBWWLVjKs/0/EG+RTqEaZOG7zsIP3ArvHqKPRU9QK6KkzP8/vxfLzXLwRI8SDuomVKFLzmamVLQc/GW8oGjihN3DfbOljchEeRbgmAHVW+MFMy7Fk3byKkKMRSCNMr3c7lQXuEHBHYBVh+MnZMx3LKtdcSbV5dlnfSgrE5nyLt75DmOrVQFtPdv6hzJxik9cEj4j8kUYTTbmQI1iW89oUl6tlp0XUSNYHKzriL2mZeI5De0YrQu+FBIW1WGBrla/HPe0aXpm02iyNQQGsE9iTUsXAvyDRy40j9+cjLnU8Ayd59HPL9Yre8/OPZ7/fc/IQdcKIOo= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/8/26 11:03 AM, Baolin Wang wrote: > > > On 9/8/26 10:34 AM, Barry Song wrote: >> On Tue, Sep 8, 2026 at 10:30 AM Baoquan He wrote: >>> >>> Hi Baolin, >>> >>> On 09/07/26 at 11:25am, Baolin Wang wrote: >>> ......snip... >>>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>>> index 40d3f1b48a74..42c0a09938ab 100644 >>>> --- a/mm/vmscan.c >>>> +++ b/mm/vmscan.c >>> >>> Well, this seems to be based on Andrew's mm-new branch. I usually track >>> mm-unstable branch. Maybe the subject should be marked as below? >>> [PATCH mm-new] mm: mglru: clear the reference counter for rejected > > ACK. > >>> >>>> @@ -5021,10 +5021,11 @@ static int evict_folios(unsigned long >>>> nr_to_scan, struct lruvec *lruvec, >>>>                } >>>> >>>>                /* don't add rejected folios to the oldest generation */ >>>> -             if (lru_gen_folio_seq(lruvec, folio, false) == >>>> min_seq[type]) { >>>> -                     folio_set_lru_refs(folio, 0); >>>> +             if (lru_gen_folio_seq(lruvec, folio, false) == >>>> min_seq[type]) >>>>                        folio_set_active(folio); >>>> -             } >>>> + >>>> +             /* See the comments on LRU_REFS_FLAGS */ >>>> +             folio_set_lru_refs(folio, 0); >>> >>> This looks like a great catch, while the code change could bring issue. >>> >>> Because move_folios_to_lru() relies on folios' flags to decide their new >>> generation. You just cleared it before move_folios_to_lru(). This is no >>> problem for rejected folios that are determined to be put into the >>> oldest generation. But for those rejected folios that are determined to >>> be promoted, this could be wrong. E.g currently gen window is 4, and a >>> folio is referenced, lru_gen_folio_seq() decides its new gen as 1, which >>> is the 2nd oldest generation. While folio_set_lru_refs(folio, 0) clear >>> referenced bit, this causes it being put into the oldest generation in >>> move_folios_to_lru(), this is not expected. > > Yes. As I discussed with Barry earlier, lru_gen_folio_seq() also needs > to be reconsidered regarding whether it should rely on PG_referenced [1]. > > For commit 6cbdd9726fb5, we didn't discuss the impact on rejected folios > either. Before commit 6cbdd9726fb5, if rejected folios did not have > PG_active set by shrink_folio_list(), evict_folios() would set PG_active > on these rejected folios. > > [1] https://lore.kernel.org/linux-mm/20260901220430.79810-1- > baohua@kernel.org/ > >> The original code looks quite weird. It even prioritizes folios >> that won't be promoted by `PG_active`. Do we need to change all >> the cases just to call `PG_active`? > > Yes. Regarding this concern, I plan to change back to the original > behavior: > >     /* See the comments on LRU_REFS_FLAGS */ >     folio_set_lru_refs(folio, 0); > >     /* don't add rejected folios to the oldest generation */ >     if (lru_gen_folio_seq(lruvec, folio, false) == min_seq[type]) >         folio_set_active(folio); > > What do you think? Just FYI, after above changes, the performance improvement on zram is no longer obvious either. I think this also answers Kairui's earlier question about why I saw a performance improvement (which seems related to commit 6cbdd9726fb5). Also, there is no obvious performance regression either. zram swap: w/o patch w/ patch sys time: 1666.5s 1628.5s