From mboxrd@z Thu Jan 1 00:00:00 1970 From: Con Kolivas Subject: Re: [PATCH] writeback: remove the internal 5% low bound on dirty_ratio Date: Mon, 23 Aug 2010 16:30:40 +1000 Message-ID: <201008231630.40892.kernel@kolivas.org> References: <20100820032506.GA6662@localhost> <20100823144248.15fbb700@notabene> <20100823062359.GA19586@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Cc: Neil Brown , KOSAKI Motohiro , Andrew Morton , "linux-kernel@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , "riel@redhat.com" , "david@fromorbit.com" , "hch@lst.de" , "axboe@kernel.dk" To: Wu Fengguang Return-path: In-Reply-To: <20100823062359.GA19586@localhost> Content-Disposition: inline Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Mon, 23 Aug 2010 04:23:59 pm Wu Fengguang wrote: > On Mon, Aug 23, 2010 at 12:42:48PM +0800, Neil Brown wrote: > > On Fri, 20 Aug 2010 15:50:54 +1000 > > > > Con Kolivas wrote: > > > On Fri, 20 Aug 2010 02:13:25 pm KOSAKI Motohiro wrote: > > > > > The dirty_ratio was silently limited to >= 5%. This is not a user > > > > > expected behavior. Let's rip it. > > > > > > > > > > It's not likely the user space will depend on the old behavior. > > > > > So the risk of breaking user space is very low. > > > > > > > > > > CC: Jan Kara > > > > > CC: Neil Brown > > > > > Signed-off-by: Wu Fengguang > > > > > > > > Thank you. > > > > Reviewed-by: KOSAKI Motohiro > > > > > > I have tried to do this in the past, and setting this value to 0 on > > > some machines caused the machine to come to a complete standstill with > > > small writes to disk. It seemed there was some kind of "minimum" amount > > > of data required by the VM before anything would make it to the disk > > > and I never quite found out where that blockade occurred. This was some > > > time ago (3 years ago) so I'm not sure if the problem has since been > > > fixed in the VM since then. I suggest you do some testing with this > > > value set to zero before approving this change. > > You are right, vm.dirty_ratio=0 will block applications for ever.. Indeed. And while you shouldn't set the lower limit to zero to avoid this problem, it doesn't answer _why_ this happens. What is this "minimum write" that blocks everything, will 1% be enough, and is it hiding another real bug somewhere in the VM? Regards, Con -- -ck -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org