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Sun, 14 Mar 2021 20:37:32 -0700 (PDT) Received: from google.com ([2620:15c:183:200:4d84:eb70:5c32:32b8]) by smtp.gmail.com with ESMTPSA id q207sm6643816iod.6.2021.03.14.20.37.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 14 Mar 2021 20:37:32 -0700 (PDT) Date: Sun, 14 Mar 2021 21:37:27 -0600 From: Yu Zhao To: Andi Kleen Cc: linux-mm@kvack.org, Alex Shi , Andrew Morton , Dave Hansen , Hillf Danton , Johannes Weiner , Joonsoo Kim , Matthew Wilcox , Mel Gorman , Michal Hocko , Roman Gushchin , Vlastimil Babka , Wei Yang , Yang Shi , Ying Huang , linux-kernel@vger.kernel.org, page-reclaim@google.com Subject: Re: [PATCH v1 10/14] mm: multigenerational lru: core Message-ID: References: <20210313075747.3781593-1-yuzhao@google.com> <20210313075747.3781593-11-yuzhao@google.com> <871rchw4x2.fsf@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <871rchw4x2.fsf@linux.intel.com> X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: BAEEC8019142 X-Stat-Signature: 5gwmmy99f49fjqq7wmsrat5xif6morus Received-SPF: none (google.com>: No applicable sender policy available) receiver=imf08; identity=mailfrom; envelope-from=""; helo=mail-io1-f53.google.com; client-ip=209.85.166.53 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615779453-173631 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun, Mar 14, 2021 at 07:02:01PM -0700, Andi Kleen wrote: > Yu Zhao writes: Hi Andi! Recovering the context a bit: err = -EBUSY; > > + > > +#ifdef CONFIG_MEMCG > > + if (memcg && atomic_read(&memcg->moving_account)) > > + goto contended; > > +#endif > > + if (!mmap_read_trylock(mm)) > > + goto contended; > > These are essentially spinloops. Surely you need a cpu_relax() somewhere? contended: ... cond_resched(); } while (err == -EAGAIN && !mm_is_oom_victim(mm) && !mm_has_migrated(mm, memcg)); So if it's contended, we break the loop. > In general for all of spinloop like constructs it would be useful to > consider how to teach lockdep about them. > > > + do { > > + old_flags = READ_ONCE(page->flags); > > + new_gen = ((old_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1; > > + VM_BUG_ON_PAGE(new_gen < 0, page); > > + if (new_gen >= 0 && new_gen != old_gen) > > + goto sort; > > + > > + new_gen = (old_gen + 1) % MAX_NR_GENS; > > + new_flags = (old_flags & ~LRU_GEN_MASK) | ((new_gen + 1UL) << LRU_GEN_PGOFF); > > + /* mark page for reclaim if pending writeback */ > > + if (front) > > + new_flags |= BIT(PG_reclaim); > > + } while (cmpxchg(&page->flags, old_flags, new_flags) != > > old_flags); > > I see this cmpxchg flags pattern a lot. Could there be some common code > factoring? Thanks for noticing this. A shorthand macro would be nice. Hmm... let me investigate. I don't know how to do this off the top of my head: A macro can be used like cmpxchg_macro() { func(); } without backslashes and it'll be expanded to do { func(); } while ();