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Wed, 23 Mar 2022 00:47:47 -0700 (PDT) MIME-Version: 1.0 References: <20220309021230.721028-1-yuzhao@google.com> <20220309021230.721028-7-yuzhao@google.com> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Wed, 23 Mar 2022 20:47:36 +1300 Message-ID: Subject: Re: [PATCH v9 06/14] mm: multi-gen LRU: minimal implementation To: Yu Zhao Cc: Andrew Morton , Linus Torvalds , Andi Kleen , Aneesh Kumar , Catalin Marinas , Dave Hansen , Hillf Danton , Jens Axboe , Jesse Barnes , Johannes Weiner , Jonathan Corbet , Matthew Wilcox , Mel Gorman , Michael Larabel , Michal Hocko , Mike Rapoport , Rik van Riel , Vlastimil Babka , Will Deacon , Ying Huang , LAK , Linux Doc Mailing List , LKML , Linux-MM , Kernel Page Reclaim v2 , x86 , Brian Geffon , Jan Alexander Steffens , Oleksandr Natalenko , Steven Barrett , Suleiman Souhlal , Daniel Byrne , Donald Carr , =?UTF-8?Q?Holger_Hoffst=C3=A4tte?= , Konstantin Kharlamov , Shuang Zhai , Sofia Trinh , Vaibhav Jain Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM, RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Mar 19, 2022 at 4:11 PM Yu Zhao wrote: > > On Fri, Mar 18, 2022 at 9:01 PM Barry Song <21cnbao@gmail.com> wrote: > > > > > +static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio, bool reclaiming) > > > +{ > > > + unsigned long old_flags, new_flags; > > > + int type = folio_is_file_lru(folio); > > > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > > > + int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]); > > > + > > > + do { > > > + new_flags = old_flags = READ_ONCE(folio->flags); > > > + VM_BUG_ON_FOLIO(!(new_flags & LRU_GEN_MASK), folio); > > > + > > > + new_gen = ((new_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1; > > > + new_gen = (old_gen + 1) % MAX_NR_GENS; > > > > new_gen is assigned twice, i assume you mean > > old_gen = ((new_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1; > > new_gen = (old_gen + 1) % MAX_NR_GENS; > > > > or do you always mean new_gen = lru_gen_from_seq(min_seq) + 1? > > Thanks a lot for your attention to details! > > The first line should be in the next patch but I overlooked during the > last refactoring: Thanks for the clarification. So an unmapped file-backed page which is accessed only by system call will always be in either min_seq or min_seq + 1? it has no chance to be in max_seq like a faulted-in mapped file page? > > new_gen = ((new_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1; > + /* folio_update_gen() has promoted this page? */ > + if (new_gen >= 0 && new_gen != old_gen) > + return new_gen; > + > new_gen = (old_gen + 1) % MAX_NR_GENS; Thanks Barry