From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bernd Schubert Subject: Re: Off-Topic Write cache disabling? Date: Wed, 04 Feb 2015 13:46:24 +0100 Message-ID: <54D214A0.7090000@fastmail.fm> References: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Weedy , linux-raid@vger.kernel.org List-Id: linux-raid.ids On 02/03/2015 06:45 PM, Weedy wrote: > Is there a kernel option or sysfs toggle that disables write caching? > Or forces the kernel to commit everything constantly. > > ------ > I don't really want to join another ML, especially a higher traffic > one just to ask this when it only bugs me sometimes. But I'll shut up > if this is unwanted. > ------ > > I use a similar kernel config with respect to selected options on all > my systems but this only effect my laptop. > On any of my personal system or system I have remote access too > nr_dirty drifts up and down and nr_writeback stays around 0 (assuming > the system isn't working hard). > On my laptop both nr_dirty and nr_writeback stay at 0. I can make them > go up to 10ish if I untar something but then almost immediately go > back to 0. If I didn't know better I would swear dirty_*_centisecs or > something was set to a near instant commit interval but I haven't > found evidence of that. The hard drive light blinks almost constantly > once a second, even if I'm at a X login screen. > As I said this doesn't bug me most of the time but if I let my FF > session get too large or start multiple VMs anything that might make > me swap a little, the machine pretty much dies from IOWAIT. Which I'm > guessing is because it's trying to flush (syncfs?) imediately and > constantly. > > You guys spend all day in the IO subsystem, any idea where I can keep > looking? It has persisted across reboots and kernel updates. Try mount -osync or force your application to write with direct IO. Cheers, Bernd