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Thu, 22 Apr 2021 13:15:39 -0700 (PDT) MIME-Version: 1.0 References: <20210416023536.168632-1-zhengjun.xing@linux.intel.com> <7b7a1c09-3d16-e199-15d2-ccea906d4a66@linux.intel.com> In-Reply-To: From: Yu Zhao Date: Thu, 22 Apr 2021 14:15:27 -0600 Message-ID: Subject: Re: [RFC] mm/vmscan.c: avoid possible long latency caused by too_many_isolated() To: Shakeel Butt Cc: Johannes Weiner , Xing Zhengjun , Andrew Morton , Linux MM , LKML , Huang Ying , Tim Chen , Michal Hocko , wfg@mail.ustc.edu.cn Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 147CAE00012B X-Stat-Signature: 1m7wa1bxttyqb58z18o4u9bb4gqrpf9s Received-SPF: none (google.com>: No applicable sender policy available) receiver=imf21; identity=mailfrom; envelope-from=""; helo=mail-wr1-f50.google.com; client-ip=209.85.221.50 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1619122537-782633 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 Thu, Apr 22, 2021 at 12:52 PM Shakeel Butt wrote: > > On Thu, Apr 22, 2021 at 10:13 AM Yu Zhao wrote: > > > [...] > > spin_lock_irq(&lruvec->lru_lock); > > @@ -3302,6 +3252,7 @@ static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist, > > unsigned long try_to_free_pages(struct zonelist *zonelist, int order, > > gfp_t gfp_mask, nodemask_t *nodemask) > > { > > + int nr_cpus; > > unsigned long nr_reclaimed; > > struct scan_control sc = { > > .nr_to_reclaim = SWAP_CLUSTER_MAX, > > @@ -3334,8 +3285,17 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order, > > set_task_reclaim_state(current, &sc.reclaim_state); > > trace_mm_vmscan_direct_reclaim_begin(order, sc.gfp_mask); > > > > + nr_cpus = current_is_kswapd() ? 0 : num_online_cpus(); > > kswapd does not call this function (directly or indirectly). > > > + while (nr_cpus && !atomic_add_unless(&pgdat->nr_reclaimers, 1, nr_cpus)) { > > At most nr_nodes * nr_cpus direct reclaimers are allowed? > > > + if (schedule_timeout_killable(HZ / 10)) > > trace_mm_vmscan_direct_reclaim_end() and set_task_reclaim_state(NULL)? > > > + return SWAP_CLUSTER_MAX; > > + } > > + > > nr_reclaimed = do_try_to_free_pages(zonelist, &sc); > > > > + if (nr_cpus) > > + atomic_dec(&pgdat->nr_reclaimers); > > + > > trace_mm_vmscan_direct_reclaim_end(nr_reclaimed); > > set_task_reclaim_state(current, NULL); > > BTW I think this approach needs to be more sophisticated. What if a > direct reclaimer within the reclaim is scheduled away and is out of > CPU quota? More sophisticated to what end? We wouldn't worry about similar scenarios that we ran out of cpu quota while holding resources like a mutex, Si why this one is different, especially given that we already allow many reclaimers to run concurrently?