From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Emelyanov Subject: Re: [PATCH] memory.min_usage (seqlock for res_counter) Date: Wed, 05 Dec 2007 12:12:22 +0300 Message-ID: <47566B76.6020102@openvz.org> References: <20071204164615.fc871e44.kamezawa.hiroyu@jp.fujitsu.com> <20071204075854.5850B1D0BFA@siro.lan> <20071204195436.77fc911b.kamezawa.hiroyu@jp.fujitsu.com> <475535B2.1020801@openvz.org> <20071205093455.0f46b456.kamezawa.hiroyu@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20071205093455.0f46b456.kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: KAMEZAWA Hiroyuki Cc: containers-qjLDD68F18O7TbgM5vRIOg@public.gmane.org, minoura-jCdQPDEk3idL9jVzuh4AOg@public.gmane.org, YAMAMOTO Takashi , balbir-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org List-Id: containers.vger.kernel.org KAMEZAWA Hiroyuki wrote: > On Tue, 04 Dec 2007 14:10:42 +0300 > Pavel Emelyanov wrote: > >> KAMEZAWA Hiroyuki wrote: >>> This is seqlock version res_counter. >>> Maybe this this will reduce # of spin_lock. >>> >>> Pavel-san, How about this ? >> AFAIS the readlock is used only in the check_under_limit(), >> but I think, that even if we read usage and limit values >> in this case non-atomically, this won't result in any >> dramatic sequence at all. No? >> > Reader can detect *any* changes in res_counter member which happens > while they access res_counter between seq_begin/seq_retry. > Memory barrier and "sequence" of seq_lock guarantees this. > So..there is no dramatical situation. > (it's used for accesing xtime.) > > I'm sorry if I miss your point. Sorry, let me explain it in other words. I think, that protection in reader, that guarantees that it will see the valid result, is not very important - even if we compare usage and limit not atomically nothing serious will happen (in this particular case) > Thanks, > -Kame > >