Messages in this thread | | | Date | Wed, 7 Jan 2004 22:10:45 +0100 | From | Jens Axboe <> | Subject | Re: 2.6.1-rc1-tiny2 |
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On Wed, Jan 07 2004, Matt Mackall wrote: > On Wed, Jan 07, 2004 at 03:06:40PM +0100, Jens Axboe wrote: > > On Mon, Jan 05 2004, Matt Mackall wrote: > > > This is the fourth release of the -tiny kernel tree. The aim of this > > > tree is to collect patches that reduce kernel disk and memory > > > footprint as well as tools for working on small systems. Target users > > > are things like embedded systems, small or legacy desktop folks, and > > > handhelds. > > > > > > Latest release includes: > > > - various compile fixes for last release > > > - actually include Andi Kleen's bloat-o-meter this time > > > - optional mempool removal > > > > Your CONFIG_MEMPOOL is completely broken as you are no longer giving the > > same guarentees (you have no reserve at all). Might as well change it to > > CONFIG_DEADLOCK instead. > > It's equivalent to a pool size of zero, yes, so deadlock odds are > significantly higher with some usage scenarios. I'll add a big fat > warning.
Precisely. In most scenarios it makes deadlocks possible, where it was safe before (more below).
> On the other hand, the existence of pre-allocated mempools can greatly > increase the likelihood of starvation, oom, and deadlock on the rest > of the system, especially as it becomes a greater percentage of the > total free memory on a small system. In other words, I had to cut this > corner to make running in 2M work with my config. When I merge > CONFIG_BLOCK, it'll be more generally useful.
It needs to be carefulled tuned, definitely.
> For the sake of our other readers, I'll point out that mempool doesn't > intrinisically reduce deadlock odds to zero unless we have a hard > limit on requests in flight that's strictly less than pool size.
That's not true, depends entirely on usage. It's not a magic wand. And you don't need a hard limit, you only need progress guarentee. Typically just a single pre-allocated object can make you 100% deadlock free, if stacking is not involved. So for most cases, I think it would be much better if you just hard wired min_nr to 1, that would move you from 90% to 99% safe :-)
-- Jens Axboe
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