From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH 5/5] writeback: Reporting dirty thresholds in /proc/vmstat Date: Mon, 13 Sep 2010 14:24:12 -0700 Message-ID: <20100913142412.dc0f6950.akpm@linux-foundation.org> References: <1284357493-20078-1-git-send-email-mrubin@google.com> <1284357493-20078-6-git-send-email-mrubin@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, fengguang.wu@intel.com, jack@suse.cz, riel@redhat.com, david@fromorbit.com, kosaki.motohiro@jp.fujitsu.com, npiggin@kernel.dk, hch@lst.de, axboe@kernel.dk To: Michael Rubin Return-path: Received: from smtp1.linux-foundation.org ([140.211.169.13]:51752 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751240Ab0IMVZR (ORCPT ); Mon, 13 Sep 2010 17:25:17 -0400 In-Reply-To: <1284357493-20078-6-git-send-email-mrubin@google.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Sun, 12 Sep 2010 22:58:13 -0700 Michael Rubin wrote: > The kernel already exposes the user desired thresholds in /proc/sys/vm > with dirty_background_ratio and background_ratio. But the kernel may > alter the number requested without giving the user any indication that > is the case. > > Knowing the actual ratios the kernel is honoring can help app developers > understand how their buffered IO will be sent to the disk. > > $ grep threshold /proc/vmstat > nr_dirty_threshold 409111 > nr_dirty_background_threshold 818223 > Yes, I think /proc/vmstat is a decent place to put these. The needed infrastructural support is minimal and although these numbers are closely tied to the implementation-of-the-day, people should expect individual fields in /proc/vmstat to appear and disappear at random as kernel versions change.