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[109.81.21.195]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-486f4214ab8sm48028185e9.6.2026.03.18.01.31.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Mar 2026 01:31:35 -0700 (PDT) Date: Wed, 18 Mar 2026 09:31:34 +0100 From: Michal Hocko To: "zhaoyang.huang" Cc: Andrew Morton , "T . J . Mercier" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Zhaoyang Huang , steve.kang@unisoc.com, Axel Rasmussen , Yuanchu Xie , Wei Xu Subject: Re: [PATCHv3] mm: remove '!root_reclaim' checking in should_abort_scan() Message-ID: References: <20260318011558.1696310-1-zhaoyang.huang@unisoc.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: <20260318011558.1696310-1-zhaoyang.huang@unisoc.com> On Wed 18-03-26 09:15:58, zhaoyang.huang wrote: > From: Zhaoyang Huang > > Android systems usually use memory.reclaim interface to implement user > space memory management which expects that the requested reclaim target > and actually reclaimed amount memory are not diverging by too much. With > the current MGRLU implementation there is, however, no bail out when the > reclaim target is reached and this could lead to an excessive reclaim > that scales with the reclaim hierarchy size.For example, we can get a > nr_reclaimed=394/nr_to_reclaim=32 proactive reclaim under a common 1-N > cgroup hierarchy. > This defect arised from the goal of keeping fairness among memcgs that > is, for try_to_free_mem_cgroup_pages -> shrink_node_memcgs -> > shrink_lruvec -> lru_gen_shrink_lruvec -> try_to_shrink_lruvec, the > !root_reclaim(sc) check was there for reclaim fairness, which was > necessary before commit 'b82b530740b9' ("mm: vmscan: restore > incremental cgroup iteration") because the fairness depended on > attempted proportional reclaim from every memcg under the target > memcg. However after commit 'b82b530740b9' there is no longer a need > to visit every memcg to ensure fairness. Let's have try_to_shrink_lruvec > bail out when the nr_reclaimed achieved. > > Suggested-by: T.J.Mercier > Reviewed-by: T.J.Mercier > Signed-off-by: Zhaoyang Huang OK, this is easier to understand. Although you have avoided some clarifications I have asked for explicitly in prior version. If MGLRU maintainers are OK with this then just go ahead. Btw. I have only now noticed that they have not been involved. Adding them now. > --- > Patchv2,v3: update commit message > --- > --- > mm/vmscan.c | 4 ---- > 1 file changed, 4 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 0fc9373e8251..10f1e7d716ca 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -4839,10 +4839,6 @@ static bool should_abort_scan(struct lruvec *lruvec, struct scan_control *sc) > int i; > enum zone_watermarks mark; > > - /* don't abort memcg reclaim to ensure fairness */ > - if (!root_reclaim(sc)) > - return false; > - > if (sc->nr_reclaimed >= max(sc->nr_to_reclaim, compact_gap(sc->order))) > return true; > > -- > 2.25.1 -- Michal Hocko SUSE Labs