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Mon, 10 Dec 2018 12:10:36 -0800 (PST) Received: by uranus.localdomain (Postfix, from userid 1000) id 405AE460AA3; Mon, 10 Dec 2018 23:10:36 +0300 (MSK) Date: Mon, 10 Dec 2018 23:10:36 +0300 From: Cyrill Gorcunov To: Kirill Tkhai Cc: akpm@linux-foundation.org, mhocko@suse.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, gorcunov@virtuozzo.com Subject: Re: [PATCH] ksm: React on changing "sleep_millisecs" parameter faster Message-ID: <20181210201036.GC2342@uranus.lan> References: <154445792450.3178.16241744401215933502.stgit@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <154445792450.3178.16241744401215933502.stgit@localhost.localdomain> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 10, 2018 at 07:06:18PM +0300, Kirill Tkhai wrote: > ksm thread unconditionally sleeps in ksm_scan_thread() > after each iteration: > > schedule_timeout_interruptible( > msecs_to_jiffies(ksm_thread_sleep_millisecs)) > > The timeout is configured in /sys/kernel/mm/ksm/sleep_millisecs. > > In case of user writes a big value by a mistake, and the thread > enters into schedule_timeout_interruptible(), it's not possible > to cancel the sleep by writing a new smaler value; the thread > is just sleeping till timeout expires. > > The patch fixes the problem by waking the thread each time > after the value is updated. > > This also may be useful for debug purposes; and also for userspace > daemons, which change sleep_millisecs value in dependence of > system load. > > Signed-off-by: Kirill Tkhai Kirill, can we rather reuse @ksm_thread variable from ksm_init (by moving it to static file level variable). Also wakening up unconditionally on write looks somehow suspicious to me though I don't have a precise argument against.