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b=lFTWJhfXpNhqkTYblYQE3A8qbRavY5KXYaF1+xBzq1BuHNn44ClyG7RVJNYgH5s1K 2nG3zF7BQykI5QG858eRRKzmhyerFraTYWkZ81LI38ORlg5Y9dCRRdSKWlKix2TyZa Pi2qKnM/QraAXsrmK34Dvq5Tj6yZMluzp8gAydyP3F0L02aVQxNEmFXWUSW7DqCiEd S+3jj2tUirDxTyehFOpEIG4AfYrrZMGbyw0HEtTs8WoAnAwzfDKcCVY8/F+IpxFAOj 9RNiI7hBGls5SxXUxRqnLOAgkh0/3stphXA3E+n5tzBUotz/SSK+s9dPdUcRTDzMZP atu4Lz6Azjbkg== From: SJ Park To: Jinjie Ruan Cc: SJ Park , akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, corbet@lwn.net, skhan@linuxfoundation.org, rdunlap@infradead.org, damon@lists.linux.dev, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH] mm/damon/reclaim: allow disabling watermarks to force reclaim of cold pages Date: Tue, 20 Oct 2026 06:58:21 -0700 Message-ID: <20261020135822.85334-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20261020133233.3920818-1-ruanjinjie@huawei.com> References: X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 86C7E40005 X-Stat-Signature: tozdtknuyizrcjnfcj1ewktotn8puniq X-Spam-Status: No, score=-9.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1792504711-333445 X-HE-Meta: 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 PQustEM+ iaK5wHNriZmmKFmM1j6BCEujY2+5n6BCBy2D7g8unuVCIS8f7PP4TRFFJwS1wP/s8jEYB8Lbxn1OJKHCeulh0iV6FyrB5qtPs8vSDxm2FRqqfZOxqzV3bxcflkTwVt9qK1Hf/mV2a8GRRrcsnVgdM34oqmxQvJ5evQgxbzc9i9oJt/cxZrSsm7zkL8FfdSlhaCQueF15/SELyIXW6ahReWGAkPJdCht/PkOyD87x+4X/2eec= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Hello Jinjie, On Tue, 20 Oct 2026 21:32:33 +0800 Jinjie Ruan wrote: > DAMON_RECLAIM runs its scheme only while the free memory rate is in > [wmarks_low, wmarks_mid]. Reclaiming cold pages raises the rate, so the > scheme self-stops as soon as memory looks plentiful again, which is wrong > for a VMM parking an idle sandbox that wants cold anonymous pages > reclaimed immediately. > > So add an ignore_wmarks module parameter. When set, the scheme uses > DAMOS_WMARK_NONE, so damos_wmark_wait_us() always returns zero and the > scheme stays active, bounded only by min_age and the quota. I agree there could be use cases that doesn't want the watermarks at all. I'd like to avoid adding new DAMON_RECLAIM parameters if possible, though. That's becasuse DAMON_RECLAIM is introduced to let people use it without complicated setups. We will of course add new parameters if really needed, but I want to see if there is a good alternative. Have you considered some other alternatives? For example, could respectively setting wmarks_high, wmarks_mid and wmarks_low to 100%, 100% and 0% effectively disable watermarks? Have you tried that? If that works, how about updating document to clearly explain the usage? Also, have you considered using DAMON sysfs interface instead of DAMON_RECLAIM? Thanks, SJ [...]