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Sat, 27 Jun 2026 14:36:42 -0700 (PDT) From: Liew Rui Yan To: sj@kernel.org Cc: aethernet65535@gmail.com, damon@lists.linux.dev, linux-mm@kvack.org Subject: Re: [RFC PATCH] mm/damon/reclaim: add 'available' memory as an optional watermarks metric Date: Sun, 28 Jun 2026 05:36:50 +0800 Message-ID: <20260627213651.19000-1-aethernet65535@gmail.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260626141819.86269-1-sj@kernel.org> References: <20260626141819.86269-1-sj@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 1610380008 X-Stat-Signature: x5xkgedib9hebj6d3j7pj6h5gwuq9beq X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1782596203-530362 X-HE-Meta: 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 cZ9AmqIF 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi SeongJae, On Fri, 26 Jun 2026 07:18:18 -0700 SeongJae Park wrote: > How about using DAMOS quota with its aim-based auto-tuning, instead? > > I developed DAMOS watermarks and quota as safe guards of DAMOS. In more > detail, DAMOS quota is for restricting only resource usage of DAMOS. > Meanwhile, watermarks is for restricting resource usage of both DAMON and > DAMOS. That is, when the watermarks condition is met, not only DAMOS but also > DAMON is completely paused. Also, watermarks feature was considered smarter > than quota, because it is a kind of auto-tuning. > > However, it turned out completely turning DAMON off is not a very good idea, > because it drops monitoring results when the watermarks condition is met and > therefore completely stops DAMON and DAMOS. It drops the region shapes and > 'age' information. Especially, 'age' of some regions commonly cumulated up to > hours or even days. Dropping that was a problem in production use cases. I looked at the code and noticed that kdamond_wait_activation() doesn't seem to free the regions, the data remains in memory. By "drops", do you mean the age information becomes stale/unreliable during the inactive period rather than being literally discarded? > > Meanwhile, we introduced aim-oriented DAMOS quota auto-tuning (a.k.a DAMOS > quota goal). It made DAMOS quota smarter and easier to extend than watermarks. > Nowadays, users can also pause and resume [1] DAMON/DAMOS without losing the > monitoring information when they want. > > So, I personally don't encourage people to use watermarks. Of course, I may > missing some problems in alternatives. Hence I'm asking the question to you. > > How about using DAMOS quota with its aim-based auto-tuning, instead? If you > cannot, could you share more details? > > I'll hold reviewing the code until this high level discussion is resolved. > > [1] https://lore.kernel.org/20260427151231.113429-1-sj@kernel.org Thank you for the detailed explanation. I now understand that watermarks pause the entire DAMON monitoring loop rather than just gating DAMOS actions. I agree this makes watermarks unsuitable for the Android use case I described. I will drop this patch. I think controlling DAMOS pause/rusume separately might be better suited for execution in user space (such as controlling‘quota_ms’ and ‘quota_sz’). By the way, I sent you an email about three weeks ago (Fri, 5 Jun 2026 20:28:00 +0800) introducing a userspace auto-tuner program I wrote for DAMON_RECLAIM's 'min_age', and asking for your thoughts. I am not sure if it reached you, could you please check? I would really appreciate your feedback on that as well. Best regards, Rui Yan