Re: [patch] radix-tree: avoid atomic allocations for preloaded insertions

[Andrew Morton <akpm@linux-foundation.org>]

> On Thu, 8 Nov 2007 05:54:04 +0100 Nick Piggin <npiggin@suse.de> wrote:
> > - doesn't solve the problem which it claims to be solving
> >   (radix_tree_insert() doesn't deplete atomic reserves as long as the
> >   caller uses radix_tree_preload(GFP_KERNEL))
> 
> I'm pretty sure it does. I don't follow exactly why you say it doesn't.
>  

I was wrong.  The radix_tree_preloads will remain full and we'll just keep
on doing GFP_ATOMIC allocations.

> > - is probably desirable as a simplify-the-locking-hierarchy thing, but a)
> >   should be presented as such and
> 
> It's primarily to avoid GFP_ATOMIC allocations. Simplify the locking
> hierarcy is secondary and I put that in the changelog.
> 
> 
> > b) needs code comments explaining why it
> >   is correct and needs a big fat TODO explaining how we should get that
> >   kmem_cache_alloc() out of there, an how we should do it.
> > 
> > OK?
> 
> I don't really know about getting that kmem_cache_alloc out of there.
> For radix trees that are protected by sleeping locks, you don't actually
> need to disable preempt and you can do sleeping allocations there.

If the radix tree's gfp_mask is GFP_ATOMIC, radix_tree_insert() can require
that the preloads be full.

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