Re: 2.6.17-rc1-mm1

[Alasdair G Kergon]

On Thu, Apr 13, 2006 at 01:13:03AM -0700, Andrew Morton wrote:
> Heiko Carstens <heiko.carstens@xxxxxxxxxx> wrote:
> >
> > > +md-dm-reduce-stack-usage-with-stacked-block-devices.patch
> > >  MD update.
> > 
> > Any chance to see this merged? I think this one is pending for quite a while.
 
I looked at this in detail last month, hoping to get it
out of the way, but unfortunately found that, in dm-crypt:

  Instead of the stack growing, we'll be allocating successive
  bios out of the *same* mempool and, without the recursion, we'll
  have lost the possibility of a later allocation waiting for an
  earlier one to be released after its endio.

In other words, I think part of dm-crypt needs re-writing to avoid problems
under memory pressure after this patch is applied.  And on the face of it,
__clone_and_map() may suffer from similar problems should a bio need to be
split into several pieces.

Alasdair
-- 
agk@xxxxxxxxxx
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