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[35.169.212.159]) by smtp.gmail.com with ESMTPSA id i21sm10382458qkl.20.2021.06.14.06.49.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 14 Jun 2021 06:49:32 -0700 (PDT) From: SeongJae Park X-Google-Original-From: SeongJae Park To: "Matthew Wilcox (Oracle)" Cc: akpm@linuxfoundation.org, linux-mm@kvack.org, Heiko Carstens , Rafael Aquini , Vlastimil Babka , Yu Zhao , Vladimir Davydov , kirill.shutemov@linux.intel.com, amit@kernel.org Subject: Re: [PATCH] mm: Mark idle page tracking as BROKEN Date: Mon, 14 Jun 2021 13:49:26 +0000 Message-Id: <20210614134926.17279-1-sjpark@amazon.de> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20210612000714.775825-1-willy@infradead.org> Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=gmail.com header.s=20161025 header.b=kMAdbvvO; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf22.hostedemail.com: domain of sj38park@gmail.com designates 209.85.219.47 as permitted sender) smtp.mailfrom=sj38park@gmail.com X-Rspamd-Server: rspam02 X-Stat-Signature: eb5fni7r9drzuwd4pqmtn5kc7hfopie4 X-Rspamd-Queue-Id: 237B7C00CBEE X-HE-Tag: 1623678565-901490 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: SeongJae Park Hello Matthew, On Sat, 12 Jun 2021 01:07:14 +0100 "Matthew Wilcox (Oracle)" wrote: > In discussion with other MM developers around how idle page tracking > should be fixed for transparent huge pages, several expressed the opinion > that it should be removed as it is inefficient at accomplishing the > job that it is supposed to, and we have better mechanisms (eg uffd) for > accomplishing the same goals these days. I think the THP case[1] is an intended behavior[2]. Could you please share a link to the discussion or a detailed summary if possible? > > Mark the feature as BROKEN for now and we can remove it entirely in a > few months if nobody complains. It is not enabled by Android, ChromeOS, > Debian, Fedora or SUSE. Red Hat enabled it with RHEL-8.1 and UEK followed > suit, but I have been unable to find why RHEL enabled it. Amazon Linux is also using it[3], for DAMON[4]. In detail, DAMON doesn't use Idle Page Tracking but PG_Idle in kernel space, to avoid interfering the reclaim logic[5]. So, I'm ok with removing the Idle Page Tracking user space interface, but gonna be opposed to removing PG_Idle. Nevertheless, the interference is not a real problem to DAMON, as DAMON is aimed to provide just a reasonable quality of the monitoring, rather than strict correctness. Hence, if people think the interference is also not a problem for the reclaim logic (after all, it does nothing unless sysadmin manually turns it on in runtime, and can be turned off at anytime), I would simply update DAMON code to don't use PG_Idle, add warnings in the doc, and wouldn't be opposed to this change. But, if not, I think this change will be a big problem to us. If the problem is a lack of dedicated maintainer for Idle Page Tracking or PG_Idle, I can volunteer. [1] https://lore.kernel.org/linux-mm/YMGKVmt8trMJ9kOP@casper.infradead.org/ [2] https://lore.kernel.org/linux-mm/20210614081610.16123-1-sjpark@amazon.de/ [3] https://github.com/amazonlinux/linux/blob/amazon-5.10.y/master/mm/damon/Kconfig#L19 [4] https://lore.kernel.org/linux-mm/20210520075629.4332-1-sj38.park@gmail.com/ [5] https://lore.kernel.org/linux-mm/20210525154427.30921-1-sjpark@amazon.de/ Thanks, SeongJae Park [...]