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b=hmX4tl3MKGsF9m/+hq1ZYLMiEusVyRG/sxJXQhGQIfDXHZ3aKnHgAAk5mLU8U4Evk 4B9xWCJIZoEU29h7oq3RtU2ZNw62xPI40xgq4r/sdkOUZqLmf4Emq3cxVuljcHYLEC O+uE+ZWL1QB2sFDY+uxCd3v9YGArQBP7yKn9cdgLHihtM6SAj/vFscY1XkfiJ/f16P U8B8w+RTVwp/G3RmKUJeFFcDB+yUlnBtWO4wNTCb/M6IpYZudbsWmq6bDMHUwefc/P nTxWREoGIlCQ8gFsZ70ACBvApQ5bV7x5+rGCHL1lYtZwb11qwuXipVSWJsVqQ4fFRp Cr98S2n6yIWUA== From: SJ Park To: Liew Rui Yan Cc: SJ Park , damon@lists.linux.dev, linux-mm@kvack.org Subject: Re: [PATCH 2/2] mm/damon: skip deactivated schemes in watermark checks and add fallback sleep Date: Fri, 7 Aug 2026 07:07:39 -0700 Message-ID: <20260807140739.91238-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260807093526.183009-3-aethernet65535@gmail.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: sijcsznrep7s66itb5umzyrw53zezz1h X-Rspamd-Queue-Id: 2CFE880012 X-HE-Tag: 1786111668-552010 X-HE-Meta: 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 UWwHlcHm Ko6lUk5p0teRdLCIQXZymV+11ziNSkcbEiZD234C7rcbApPBTv1A40CmVcKPOmmTLe5Zzvn/FgU/nFnOj+P0QQw9xkjq0TJu4RwYz1pgdPMStpJmSONLt26q4G5yYNz8yNBIDGpenCY8Zyqrm/SgwPSQGzxywn25EuYjNkBax6znMVzDo5hn1uekGmDd+m8tIix6bYFvVTNs4IRUAeG1pbkmwUP6tq7lVvYS+1Bj7JNNkAfE= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hello Liew, On Fri, 7 Aug 2026 17:35:26 +0800 Liew Rui Yan wrote: > According to DAMOS design documentation, a scheme is deactivated when > nr_snapshots reaches max_nr_snapshots. However, the previous > kdamond_wait_activation() still checked the schemes which nr_snapshots > reached max_nr_snapshots. > > This caused an issue - when all schemes were deactivated due to > max_nr_snapshots, but their watermarks were still satisfied, > damos_wmark_wait_us() would return 0, causing kdamond_wait_activation() > to return 0 (activated). The main loop would then continue without > sleeping, leading to unnecessary overhead since all schemes would be > skipped in damon_do_apply_schemes(). This is an intended implementation. When all schemes are deactivated by watermarks, DAMON stops monitoring. It was implemented in the way because we didn't want DAMON consumes system resource in the case. But, later it turned out DAMON's resource consumption is really negligible. Rather, it is turned out that it makes DAMON runs with stale history when it is activated again. Particularly, regions have 'age' and their start/end addresses that was emerged before the deactivation. Those are meaningless and could even cause wrong DAMOS decisions. We don't want that anymore. For a case the user really want DAMON completely stops, we introduced 'pause'. For max_nr_snapshot-based deactivation, we don't intend to completely stop DAMON. Maybe the documentation can be updated to further clarify this. Thanks, SJ [...]