On Wed, 3 Oct 2012, Jeff Moyer wrote: > Date: Wed, 03 Oct 2012 10:30:54 -0400 > From: Jeff Moyer <jmo...@redhat.com> > To: Dave Chinner <dchin...@redhat.com> > Cc: Lukáš Czerner <lczer...@redhat.com>, Jens Axboe <ax...@kernel.dk>, > linux-kernel@vger.kernel.org > Subject: Re: [PATCH] loop: Limit the number of requests in the bio list > > Dave Chinner <dchin...@redhat.com> writes: > > > On Tue, Oct 02, 2012 at 10:52:05AM +0200, Lukáš Czerner wrote: > >> On Mon, 1 Oct 2012, Jeff Moyer wrote: > >> > Date: Mon, 01 Oct 2012 12:52:19 -0400 > >> > From: Jeff Moyer <jmo...@redhat.com> > >> > To: Lukas Czerner <lczer...@redhat.com> > >> > Cc: Jens Axboe <ax...@kernel.dk>, linux-kernel@vger.kernel.org, > >> > Dave Chinner <dchin...@redhat.com> > >> > Subject: Re: [PATCH] loop: Limit the number of requests in the bio list > >> > > >> > Lukas Czerner <lczer...@redhat.com> writes: > >> > > >> > > Currently there is not limitation of number of requests in the loop bio > >> > > list. This can lead into some nasty situations when the caller spawns > >> > > tons of bio requests taking huge amount of memory. This is even more > >> > > obvious with discard where blkdev_issue_discard() will submit all bios > >> > > for the range and wait for them to finish afterwards. On really big > >> > > loop > >> > > devices this can lead to OOM situation as reported by Dave Chinner. > >> > > > >> > > With this patch we will wait in loop_make_request() if the number of > >> > > bios in the loop bio list would exceed 'nr_requests' number of > >> > > requests. > >> > > We'll wake up the process as we process the bios form the list. > >> > > >> > I think you might want to do something similar to what is done for > >> > request_queues by implementing a congestion on and off threshold. As > >> > Jens writes in this commit (predating the conversion to git): > >> > >> Right, I've had the same idea. However my first proof-of-concept > >> worked quite well without this and my simple performance testing did > >> not show any regression. > > Did you look at system time? > > -Jeff
Hi, none of the times showed any significant difference, there was not any pattern suggesting a problem. Also the system time is included in the real time, so it would show anyway I guess. -Lukas
