[dm-devel] dm: Make MIN_IOS, et al, tunable via sysctl.
Mikulas Patocka
mpatocka at redhat.com
Tue Aug 20 21:44:39 UTC 2013
On Mon, 19 Aug 2013, Frank Mayhar wrote:
> On Mon, 2013-08-19 at 10:00 -0400, Mike Snitzer wrote:
> > Performance isn't the concern. The concern is: does DM allow for
> > forward progress if the system's memory is completely exhausted?
> >
> > This is why request-based has such an extensive reserve, because it
> > needs to account for cloning the largest possible request that comes in
> > (with multiple bios).
>
> Thanks for the response. In our particular case, I/O will be file
> system based and over a network, which makes it pretty easy for us to be
> sure that large I/Os never happen. That notwithstanding, however, as
> you said it just seems reasonable to make these values configurable.
>
> I'm also looking at making some similar constants in dm-verity and
> dm-bufio configurable in the same way and for similar reasons.
Regarding dm-bufio: the user of dm-bufio sets the pool size as an argument
in dm_bufio_client_create. There is no need to make it configurable - if
the user selects too low value, deadlock is possible, if the user selects
too high value, there is no additional advantage.
Regarding dm-verity: the mempool size is 4, there is no need to make it
bigger, there is no advantage from that.
Mikulas
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