From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with ESMTP id 7E5BF8D0039 for ; Thu, 3 Mar 2011 20:55:38 -0500 (EST) Received: by iyf13 with SMTP id 13so1987887iyf.14 for ; Thu, 03 Mar 2011 17:55:36 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20110303104430.B93F.A69D9226@jp.fujitsu.com> References: <20110303104430.B93F.A69D9226@jp.fujitsu.com> Date: Fri, 4 Mar 2011 09:55:36 +0800 Message-ID: Subject: Re: [RFC PATCH 0/5] Add accountings for Page Cache From: Liu Yuan Content-Type: multipart/alternative; boundary=20cf30549ed9318e30049d9e7195 Sender: owner-linux-mm@kvack.org List-ID: To: KOSAKI Motohiro Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, jaxboe@fusionio.com, akpm@linux-foundation.org, fengguang.wu@intel.com --20cf30549ed9318e30049d9e7195 Content-Type: text/plain; charset=ISO-8859-1 On Thu, Mar 3, 2011 at 9:50 AM, KOSAKI Motohiro < kosaki.motohiro@jp.fujitsu.com> wrote: > > [Summery] > > > > In order to evaluate page cache efficiency, system admins are happy to > > know whether a block of data is cached for subsequent use, or whether > > the page is read-in but seldom used. This patch extends an effort to > > provide such kind of information. We adds three counters, which are > > exported to the user space, for the Page Cache that is almost > > transparent to the applications. This would benifit some heavy page > > cache users that might try to tune the performance in hybrid storage > > situation. > > I think you need to explain exact and concrete use-case. Typically, > cache-hit ratio doesn't help administrator at all. because merely backup > operation (eg. cp, dd, et al) makes prenty cache-miss. But it is no sign > of memory shortage. Usually, vmscan stastics may help memroy utilization > obzavation. > > Plus, as ingo said, you have to consider to use trancepoint framework > at first. Because, it is zero cost if an admin don't enable such > tracepoint. > > Thanks very much for your comments. Yeah, we'er going to try tracepoint and perf as Ingo said. > At last, I don't think disk_stats have to have page cache stastics. It > seems > slightly layer violation. > > Thanks. > > This is the starting point of the patch set, so I simply embedded the structure into the existing infrastructure. This did saved me a lot of effort because disk_stats is a good place to collect stats on _partition_ basis. Anyway, as you pointed out, this is kind of the mess. Thanks, Yuan --20cf30549ed9318e30049d9e7195 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable

On Thu, Mar 3, 2011 at 9:50 AM, KOSAKI M= otohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
> [Summery]
>
> In order to evaluate page cache efficiency, system admins are happy to=
> know whether a block of data is cached for subsequent use, or whether<= br> > the page is read-in but seldom used. This patch extends an effort to > provide such kind of information. We adds three counters, which are > exported to the user space, for the Page Cache that is almost
> transparent to the applications. This would benifit some heavy page > cache users that might try to tune the performance in hybrid storage > situation.

I think you need to explain exact and concrete use-case. Typically, cache-hit ratio doesn't help administrator at all. because merely backu= p
operation (eg. cp, dd, et al) makes prenty cache-miss. But it is no sign of memory shortage. Usually, vmscan stastics may help memroy utilization obzavation.

Plus, as ingo said, you have to consider to use trancepoint framework
at first. Because, it is zero cost if an admin don't enable such tracep= oint.


Thanks very much for your comments.

Yeah, = we'er going to try tracepoint and perf as Ingo said.
=A0
At last, I don't think disk_stats have to have page cache stastics. It = seems
slightly layer violation.

Thanks.


This is the starting point of the patch set, so I= simply embedded the structure into the existing infrastructure. This did s= aved me a lot of effort because disk_stats is a good place to collect stats= on _partition_=A0 basis. Anyway, as you pointed out, this is kind of the m= ess.

Thanks,
Yuan
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