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Sun, 30 Aug 2026 10:57:06 +0000 X-Mizu-Trace-ID: a1b9075004b6ac5b X-Migadu-Flow: FLOW_OUT Message-ID: Date: Sun, 30 Aug 2026 18:56:53 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/2] mm/mglru: fix ineffective memory protection for non-kswapd reclaim To: Barry Song Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Andrew Morton , Muchun Song , Kairui Song , Qi Zheng , Axel Rasmussen , Yuanchu Xie , Wei Xu , David Hildenbrand , Lorenzo Stoakes , Chris Down , Tejun Heo , Yu Zhao , "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" , "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" , linux-kernel@vger.kernel.org, Ridong Chen , stable@vger.kernel.org References: <20260828110919.1324028-1-ridong.chen@linux.dev> <20260828110919.1324028-3-ridong.chen@linux.dev> From: Ridong Chen In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 05E771C0002 X-Stat-Signature: 7wsm8i9hgg9cba3rehgwa1kr34xraw93 X-HE-Tag: 1788087437-732473 X-HE-Meta: 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 90CQLElu Vcez2WxUEl0czhnK9MIF1DcBFcWPccF8yO9flpuODYg4wf9k5B+sLujbqfmpBJEOpXEfqoPdGRyqmHe7n7gZWSRhDRwS+/4Zy5Lsqs0fLUVRAwxxTlIpreTAJ9fu7Fe+cmfyEN4ZM6cP/J0KZfChpqRPZdRTEb3o8wps6nefn6v98uKx6wiorlGV/hg6C/oyKIEeNiXD6pppMcq41LNrIhBtgg9KYnKq4CviQ3ZyOmzJv62MLIKMXiyszXmZJ2Tn36IC/EI70lhfRPizouYIIrUMHc8rpriS7mLdcZywLBieFSKR2dkaj3AxKbN6SbfTEmT+j00aeDb4D4/0= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/30/2026 6:40 PM, Barry Song wrote: > On Sun, Aug 30, 2026 at 6:13 PM Ridong Chen wrote: >> >> >> >> On 8/30/2026 3:53 PM, Barry Song wrote: >>> On Fri, Aug 28, 2026 at 7:10 PM Ridong Chen wrote: >>>> >>>> From: Ridong Chen >>>> >>>> memory.min/low is silently bypassed for MGLRU during global proactive >>>> reclaim (writing to the root memory.reclaim) and global direct reclaim. >>> >>> I guess nobody is silently bypassing anything. It's just that the >>> effective min is stale data. If kswapd has run at least once, should >>> the protection have been updated already? >>> I guess we need to update the changelog a bit? >>> >> >> The children's emin/elow are derived from the parent's min/low settings and >> children_min_usage, both of which can change over time. As a result, emin/elow >> may become stale, even if kswapd has already run once. > > right, let's just say this in changelog, we are *not* bypassing we are > just checking > against stable data. The current changelog seems to be misleading. > Thanks, Will update. > [...] >>>> +void mem_cgroup_protection_path(struct mem_cgroup *root, >>>> + struct mem_cgroup *memcg) >>> >>> Can we rename it to `mem_cgroup_calculate_protection_path()`? >>> >>> BTW, I see that the only caller is in vmscan and it passes NULL as >>> `root`. Do we need to keep the `root` argument if the new helper is >>> only used for global reclaim? >>> >> I'd suggest keeping it as is. This function updates protection along the path >> from root to memcg, and could be reused later. Note that >> mem_cgroup_calculate_protection() assumes the caller has already performed the >> top-down walk, each level's calculation depends on its parent being updated first. >> >> For mem_cgroup_calculate_protection_path(), it can be called in any context >> without such a precondition. > > I am fine with this - keeping the root there. but I guess rename is worth it. > Yeah, I will rename in the next version. -- Best regards Ridong