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[109.81.95.153]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47f464b7f84sm7267657f8f.27.2026.07.14.04.34.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Jul 2026 04:34:09 -0700 (PDT) Date: Tue, 14 Jul 2026 13:34:08 +0200 From: Michal Hocko To: Altan Hacigumus Cc: Andrew Morton , David Hildenbrand , Johannes Weiner , Kairui Song , Qi Zheng , Shakeel Butt , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Jiayuan Chen , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/vmscan: clear hopeless kswapd when global direct reclaim makes progress Message-ID: References: <20260710024429.70923-1-ahacigu.linux@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260710024429.70923-1-ahacigu.linux@gmail.com> On Thu 09-07-26 19:44:29, Altan Hacigumus wrote: > Direct reclaim clears the hopeless kswapd state only once the node > becomes balanced. This avoids cgroup memory.high reclaim repeatedly > reviving a kswapd that cannot balance the node. > > However, it also prevents global direct reclaim from reviving kswapd. > Under sustained memory pressure, global direct reclaim may continue > making progress without the node ever reaching the high watermark, > leaving reclaim to allocating tasks. > > Unlike memcg reclaim, global direct reclaim follows the same node-wide > reclaim path as kswapd. Clear the hopeless state when global direct > reclaim makes progress, while continuing to require a balanced node for > memcg reclaim. kswapd_try_clear_hopeless() becomes static since struct > scan_control is private to vmscan.c. > > On a workload with most memory mlocked and the remainder under sustained > churn, with swap enabled, comparing the same 60s window: > base patched > allocstall (all zones) 413441 6532 > pgsteal_direct 15889552 255619 > pgsteal_kswapd 0 26079382 > PSI memory full avg60 13.10% 9.37% > > Direct reclaim was already reclaiming many pages in the baseline; > this change lets kswapd resume doing that work asynchronously. > > Signed-off-by: Altan Hacigumus > --- > include/linux/mmzone.h | 2 -- > mm/vmscan.c | 23 ++++++++++++++--------- > 2 files changed, 14 insertions(+), 11 deletions(-) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index ca2712187147..1db6f8dac927 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -1630,8 +1630,6 @@ enum kswapd_clear_hopeless_reason { > > void wakeup_kswapd(struct zone *zone, gfp_t gfp_mask, int order, > enum zone_type highest_zoneidx); > -void kswapd_try_clear_hopeless(struct pglist_data *pgdat, > - unsigned int order, int highest_zoneidx); > void kswapd_clear_hopeless(pg_data_t *pgdat, enum kswapd_clear_hopeless_reason reason); > bool kswapd_test_hopeless(pg_data_t *pgdat); > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 35c3bb15ae96..78fd35a11eee 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -198,6 +198,9 @@ struct scan_control { > */ > int vm_swappiness = 60; > > +static void kswapd_try_clear_hopeless(struct pglist_data *pgdat, > + struct scan_control *sc); > + > #ifdef CONFIG_MEMCG > > /* Returns true for reclaim through cgroup limits or cgroup interfaces. */ > @@ -5172,7 +5175,7 @@ static void lru_gen_shrink_node(struct pglist_data *pgdat, struct scan_control * > blk_finish_plug(&plug); > done: > if (sc->nr_reclaimed > reclaimed) > - kswapd_try_clear_hopeless(pgdat, sc->order, sc->reclaim_idx); > + kswapd_try_clear_hopeless(pgdat, sc); > } > > /****************************************************************************** > @@ -6251,7 +6254,7 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc) > * successful direct reclaim run will revive a dormant kswapd. > */ > if (reclaimable) > - kswapd_try_clear_hopeless(pgdat, sc->order, sc->reclaim_idx); > + kswapd_try_clear_hopeless(pgdat, sc); > else if (sc->cache_trim_mode) > sc->cache_trim_mode_failed = 1; > } > @@ -7530,15 +7533,17 @@ void kswapd_clear_hopeless(pg_data_t *pgdat, enum kswapd_clear_hopeless_reason r > } > > /* > - * Reset kswapd_failures only when the node is balanced. Without this > - * check, successful direct reclaim (e.g., from cgroup memory.high > - * throttling) can keep resetting kswapd_failures even when the node > - * cannot be balanced, causing kswapd to run endlessly. > + * Reset kswapd_failures when the node is balanced, or when global > + * direct reclaim makes progress - then kswapd can make progress too. > + * Memcg reclaim can succeed where kswapd cannot (memcg protection is > + * not enforced against the reclaim target), so its progress resets > + * kswapd_failures only when the node is balanced. > */ > -void kswapd_try_clear_hopeless(struct pglist_data *pgdat, > - unsigned int order, int highest_zoneidx) > +static void kswapd_try_clear_hopeless(struct pglist_data *pgdat, > + struct scan_control *sc) > { > - if (pgdat_balanced(pgdat, order, highest_zoneidx)) > + if ((!current_is_kswapd() && !cgroup_reclaim(sc)) || > + pgdat_balanced(pgdat, sc->order, sc->reclaim_idx)) > kswapd_clear_hopeless(pgdat, current_is_kswapd() ? > KSWAPD_CLEAR_HOPELESS_KSWAPD : KSWAPD_CLEAR_HOPELESS_DIRECT); Is there any particular reason why pgdat_balanced is evaluated for cgroup_reclaim? Shouldn't this be global reclaim logic only? I.e. if (cgroup_reclaim(sc)) return; if (!current_is_kswapd() || pgdat_balanced(pgdat, sc->order, sc->reclaim_idx)) kswapd_clear_hopeless(pgdat, current_is_kswapd() ? KSWAPD_CLEAR_HOPELESS_KSWAPD : KSWAPD_CLEAR_HOPELESS_DIRECT); > } > -- > 2.55.0 -- Michal Hocko SUSE Labs