From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 92996221DB6; Fri, 24 Apr 2026 00:26:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776990394; cv=none; b=lF1fNDKDtSvWrGN0n2p5656X23HUU9f+IuqCbZ6G4RCbGoc4DG5aCuuoF7zNVgUItuiUa+oQ3yJ34C3iZVMX1Wy78PgV71+IYTsoGdWcuc7LVfVqSSejPOGy40EFwxYSCAwbE/uldk4zOHIWCKVtwUfVbthaBIKNxOANo8+lpPg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776990394; c=relaxed/simple; bh=Wj7MBRLrssfpOdJSw3iPqXTN5nRgvGJm3FItsgv+Vek=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=b1yxQvD55LWvImukYQPV2/bMS3oDHgn0WtZ/TDr5qjWe3SWPwHJ5gQ7y+C+fcFONkGs8XeWtiOJYmJVtbfd9j7t/8r6bTCDO1QrgCV20sSEpPANafEcO+M6VSwiuZfxaMZDNIl3KkigsWnzVataKPo4o1QyukWcYd0iemmzkxn8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=uYLMGkPr; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="uYLMGkPr" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8E894C2BCAF; Fri, 24 Apr 2026 00:26:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776990394; bh=Wj7MBRLrssfpOdJSw3iPqXTN5nRgvGJm3FItsgv+Vek=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=uYLMGkPr0oW877jQr7py4WfT5WNcb+zqX5VW9F0jPSCMZMSt0lCf5ALSrINIqmnVV QHzk88X1JWZxm+UGrHtWamlGKFJkroxYKtbF/b4Sm9x4qdo1w0N7VcJ0mjzj5jojhe U8HfOu9LA/tNbClE2Zn7i7SJ2Hy/R7Pz0fIFl8+8Us+yiNYUC19q1lhFxBZ7bUg/Os RzyLOX9meKjztf+SxOH/spUDLPvmlptEc6ZiyERnVJgRu0RtuABlov0LF1IkeGu/0C TPyYkmHDEnNcADg/RgN8rhUAU4Z26WaG9QN3I5b975Eg4YL+Pn3OP07NTQFp3huU/1 72uQgg7v+ZBlw== From: SeongJae Park To: Peter Xu Cc: SeongJae Park , Kiryl Shutsemau , "David Hildenbrand (Arm)" , Andrew Morton , Lorenzo Stoakes , Mike Rapoport , Suren Baghdasaryan , Vlastimil Babka , "Liam R . Howlett" , Zi Yan , Jonathan Corbet , Shuah Khan , Sean Christopherson , Paolo Bonzini , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [RFC, PATCH 00/12] userfaultfd: working set tracking for VM guest memory Date: Thu, 23 Apr 2026 17:26:24 -0700 Message-ID: <20260424002625.89857-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Thu, 23 Apr 2026 14:57:34 -0400 Peter Xu wrote: > On Thu, Apr 23, 2026 at 07:08:00PM +0100, Kiryl Shutsemau wrote: > > On Thu, Apr 23, 2026 at 10:50:06AM -0400, Peter Xu wrote: [...] > > > - Whether we have explored other approaches on page hotness tracking [...] > > DAMON is built around sampling. It is good for working set estimation, > > but I don't think it is directly useful for eviction decision. It can > > miss hot pages. LRU rotation will also loose info. > > Exactly. If we need to collect ACCESS bit (or anything similar) for > eviction accuracy pusrpose, IIUC we need per-page info, we can't estimate > by sampling. That's a fair argument. Nonetheless, there are some companies who use DAMON [1] for a similar eviction purpose on their products. Also, page level accuracy issue was indeed concerns from many people. DAMON therefore provides page level DAMOS filter [2]. The idea is finding a large region of cold pages in low overhead first, then do page level access recheck on page of the region using the filter, just before doing the eviction. DAMON-based memory tiering also uses it [3], to avoid wrongly promoting/demoting cold/hot pages in DAMON-claimed hot/cold regions. The evaluation result was not very bad, and a few more users reported positive test results. Also, DAMON can be used for page level monitoring [5] and open to changes for users. Actually a work [6] for making DAMON-based page level monitoring more lightweight is ongoing. I understand no one fits all and the decision is up to each user :) Nevertheless, I will be happy to help if you have any question or request for DAMON. [1] https://cdn.amazon.science/ee/a4/41ff11374f2f865e5e24de11bd17/resource-management-in-aurora-serverless.pdf [2] https://origin.kernel.org/doc/html/latest/mm/damon/design.html#filters [3] https://github.com/damonitor/damo/blob/next/scripts/mem_tier.sh#L40 [4] https://www.phoronix.com/news/DAMON-Self-Tuned-Memory-Tiering [5] https://origin.kernel.org/doc/html/latest/mm/damon/faq.html#can-i-simply-monitor-page-granularity [6] https://lore.kernel.org/20260423004211.7037-1-akinobu.mita@gmail.com Thanks, SJ [...]