From mboxrd@z Thu Jan 1 00:00:00 1970 From: Frank Mayhar Subject: Re: dm: Make MIN_IOS, et al, tunable via sysctl. Date: Thu, 22 Aug 2013 10:26:49 -0700 Message-ID: <1377192409.24869.116.camel@bobble.lax.corp.google.com> References: <1376070533.26057.244.camel@bobble.lax.corp.google.com> <1377034118.24869.48.camel@bobble.lax.corp.google.com> <1377035833.24869.57.camel@bobble.lax.corp.google.com> <20130820222439.GA5883@redhat.com> <1377040462.24869.70.camel@bobble.lax.corp.google.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1377040462.24869.70.camel@bobble.lax.corp.google.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Mike Snitzer Cc: device-mapper development , Mikulas Patocka List-Id: dm-devel.ids On Tue, 2013-08-20 at 16:14 -0700, Frank Mayhar wrote: > On Tue, 2013-08-20 at 18:24 -0400, Mike Snitzer wrote: > > Mikulas' point is that you cannot reduce the size to smaller than 1. > > And aside from rq-based DM, 1 is sufficient to allow for forward > > progress even when memory is completely consumed. > > > > A patch that simply changes them to 1 but makes the rq-based DM > > mempool's size configurable should actually be fine. > > So you're saying that I should submit a patch to drop the pool size for > BIO_BASED to 1 and make the pool size for REQUEST_BASED configurable? > At the moment, in dm.c the former is hardcoded to 16 and the latter is > set via MIN_IOS (currently 256). There's also io_pool, a slab pool, > which is also set via MIN_IOS. > > How does this relate to the rest of the DM modules? Mpath also sets > MIN_IOS to 256 and creates a slab pool from that, and there are a number > of hardcoded constants in dm-io (MIN_IOS and MIN_BIOS), dm-snap > (MIN_IOS), dm-crypt (MIN_IOS and MIN_POOL_PAGES), dm-bufio > (DM_BUFIO_HASH_BITS, which is allocated via vmalloc per client) and > dm-verity (DM_VERITY_MEMPOOL_SIZE, which is allocated per device). > > For the most part I can't imagine that people will want to change these > from their defaults, but when someone does need to change one of these, > they need to do so badly and there's currently no good way to do that > besides hacking the source and building a new kernel. > > By the way, I do appreciate the advice. I'm just trying to clear up > confusion on my part, make sure that our needs are met and, while I'm at > it, make things a bit better for those who come after me. Ping? Can one of you guys answer my question, here? Thanks! -- Frank Mayhar 310-460-4042