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Fri, 27 Mar 2026 09:41:09 -0700 (PDT) Date: Fri, 27 Mar 2026 12:41:06 -0400 From: Johannes Weiner To: Baolin Wang Cc: akpm@linux-foundation.org, david@kernel.org, mhocko@kernel.org, zhengqi.arch@bytedance.com, shakeel.butt@linux.dev, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, ljs@kernel.org, baohua@kernel.org, kasong@tencent.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: vmscan: fix dirty folios throttling on cgroup v1 for MGLRU Message-ID: References: <3445af0f09e8ca945492e052e82594f8c4f2e2f6.1774606060.git.baolin.wang@linux.alibaba.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: <3445af0f09e8ca945492e052e82594f8c4f2e2f6.1774606060.git.baolin.wang@linux.alibaba.com> On Fri, Mar 27, 2026 at 06:21:08PM +0800, Baolin Wang wrote: > The balance_dirty_pages() won't do the dirty folios throttling on cgroupv1. > See commit 9badce000e2c ("cgroup, writeback: don't enable cgroup writeback > on traditional hierarchies"). > > Moreover, after commit 6b0dfabb3555 ("fs: Remove aops->writepage"), we no > longer attempt to write back filesystem folios through reclaim. > > On large memory systems, the flusher may not be able to write back quickly > enough. Consequently, MGLRU will encounter many folios that are already > under writeback. Since we cannot reclaim these dirty folios, the system > may run out of memory and trigger the OOM killer. > > Hence, for cgroup v1, let's throttle reclaim after waking up the flusher, > which is similar to commit 81a70c21d917 ("mm/cgroup/reclaim: fix dirty > pages throttling on cgroup v1"), to avoid unnecessary OOM. This fix for cgroup1 makes sense to me. For cgroup2, MGLRU shares the shrink_node() reclaim throttling. Acked-by: Johannes Weiner The remaining notable difference is global reclaim. I don't see any equivalent throttling in the lru_gen_shrink_node() path. What prevents premature OOMs at the system level?