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b=NBk6qmF8iZEJg+NsOK3eEgkgxOcDwOqRxoIuUt0GzXQu1/XQUkUgVlzrn0hLrfoVu mckAZ9s+cFfGxaxbJ1bAAJBgmKiTbRmeuRSdB8wXTBAUc7cX3LdSykrs5VnIi/r+BM FrQr7oyDZ4OyL/iK8+vVgQ7h4zfAy9wttqu7be95XZDNZUPamRs7WexCOn7/3+zH6h ox/b2s3MgaIsSOspUPFFWxHiFrUadpWuVyNDQo8Zd4eGAQOg1f9KSmNmhWnRdk5Foz VDuH2fAjZMm3ThAZuOBQh5SVbFprlYZMpWL6SUAtfQ35pBnkn6pkADff1QwuQV5imE 2uMirtlf9M7Rg== From: SeongJae Park To: Quanmin Yan Cc: SeongJae Park , akpm@linux-foundation.org, damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, wangkefeng.wang@huawei.com, zuoze1@huawei.com Subject: Re: [PATCH v2 2/2] mm/damon/sysfs: change next_update_jiffies to a global variable Date: Thu, 30 Oct 2025 07:32:20 -0700 Message-ID: <20251030143221.46859-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20251030020746.967174-3-yanquanmin1@huawei.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: A91151A0019 X-Stat-Signature: uja5fgwk84bwbjmkwzzax77stc3kg1iz X-Rspam-User: X-HE-Tag: 1761834749-216707 X-HE-Meta: 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 objjFjnM KlcoZl+aNvJn6aFConmEG/9Xjzc/7rvZ0yQAt/3RXuWroP3zZAvSSaccaaN3ofnDCXAde9G+k5/8KWd4TJaDftxgjfHyZDIPwUCLgRq7NXf3VTmQaWoe1U4Ry7+Xxvm0Rrw6Atlix4GAw244iEOA4f+bNOaS+bSoHVxbasXcQymOOX2XU8q6SgBmUKMRwQSUC/+394cWRELbtcWlS025c9O93oXCeUXLQy0nTB8DtaM39mHvh9d4SGRBl4G/WNXf2iNu8o5deT4kTOOHzbThUctHqlOzdNNCT+fnmmMp0Pa+6v1YxD/+oRyvzfG72ipu2bvtB/rwHbUdSQvC7uJXykPzbFSqVZ8nqtuR3ROB5N03vShM= 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: List-Subscribe: List-Unsubscribe: On Thu, 30 Oct 2025 10:07:46 +0800 Quanmin Yan wrote: > In DAMON’s damon_sysfs_repeat_call_fn(), time_before() is used to compare > the current jiffies with next_update_jiffies to determine whether to > update the sysfs files at this moment. > > On 32-bit systems, the kernel initializes jiffies to "-5 minutes" to make > jiffies wrap bugs appear earlier. However, this causes time_before() in > damon_sysfs_repeat_call_fn() to unexpectedly return true during the first > 5 minutes after boot on 32-bit systems (see [1] for more explanation, > which fixes another jiffies-related issue before). As a result, DAMON > does not update sysfs files during that period. > > There is also an issue unrelated to the system’s word size[2]: if the > user stops DAMON just after next_update_jiffies is updated and restarts > it after 'refresh_ms' or a longer delay, next_update_jiffies will retain > an older value, causing time_before() to return false and the update to > happen earlier than expected. > > Fix these issues by making next_update_jiffies a global variable and > initializing it each time DAMON is started. > > [1] https://lkml.kernel.org/r/20250822025057.1740854-1-ekffu200098@gmail.com > [2] https://lore.kernel.org/all/20251029013038.66625-1-sj@kernel.org/ Thank you for finding and fixing these! > > Fixes: d809a7c64ba8 ("mm/damon/sysfs: implement refresh_ms file internal work") > Suggested-by: SeongJae Park > Signed-off-by: Quanmin Yan Reviewed-by: SeongJae Park Thanks, SJ [...]