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From: Shakeel Butt To: Chen Ridong Cc: akpm@linux-foundation.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, david@kernel.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, corbet@lwn.net, hannes@cmpxchg.org, roman.gushchin@linux.dev, muchun.song@linux.dev, zhengqi.arch@bytedance.com, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, lujialin4@huawei.com, zhongjinji@honor.com Subject: Re: [PATCH -next 1/5] mm/mglru: use mem_cgroup_iter for global reclaim Message-ID: References: <20251209012557.1949239-1-chenridong@huaweicloud.com> <20251209012557.1949239-2-chenridong@huaweicloud.com> <702b6c0b-5e65-4f55-9a2f-4d07c3a84e39@huaweicloud.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <702b6c0b-5e65-4f55-9a2f-4d07c3a84e39@huaweicloud.com> X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam02 X-Stat-Signature: 49zbcxgn6hx49ibw9bfodisc1utkzbba X-Rspam-User: X-Rspamd-Queue-Id: B964040015 X-HE-Tag: 1766438300-446140 X-HE-Meta: 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 dRHYEUeU 3t+239oT8LVQWhfbqQqGTG6svH0+IT5AfXNuDmd0ecBOJF/3OxWWc7GFIKiLEoV97OIPdt3X98W9c/mNbvbcNJYGv2R1mhikyIX3U/98qwmc3j5g7LYqTqpKBoLWfbqePv2dhFCpCpTIE7cRSq+BDaw/Du7rJcbOniqxlCg0go16oRZuL10KEDUHnBbamfgpvJzQVw2JpgUCas2JpgWRZc/hdGgeYFdou5/VojHKADg6BQs5JKepLKvuAWWxEBTdXUqlExGBYi0Flu21uIFx9rM5/Vw== 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: List-Subscribe: List-Unsubscribe: On Mon, Dec 22, 2025 at 03:27:26PM +0800, Chen Ridong wrote: > [...] > > >> - if (should_abort_scan(lruvec, sc)) > >> + if (should_abort_scan(lruvec, sc)) { > >> + if (cookie) > >> + mem_cgroup_iter_break(target, memcg); > >> break; > > > > This seems buggy as we may break the loop without calling > > mem_cgroup_iter_break(). I think for kswapd the cookie will be NULL and > > if should_abort_scan() returns true, we will break the loop without > > calling mem_cgroup_iter_break() and will leak a reference to memcg. > > > > Thank you for catching that—my mistake. > > This also brings up another point: In kswapd, the traditional LRU iterates through all memcgs, but > stops for the generational LRU (GENLRU) when should_abort_scan is met (i.e., enough pages are > reclaimed or the watermark is satisfied). Shouldn't both behave consistently? > > Perhaps we should add should_abort_scan(lruvec, sc) in shrink_node_memcgs for the traditional LRU as > well? We definitely should discuss about should_abort_scan() for traditional reclaim but to keep things simple, let's do that after this series. For now, follow Johannes' suggestion of lru_gen_should_abort_scan().