linux-kernel - Re: [PATCH] idr: Document ida tree sections

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Message-ID: <20130813225927.GA2000@kmo-pixel>
Date:	Tue, 13 Aug 2013 15:59:27 -0700
From:	Kent Overstreet <kmo@...erainc.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Fengguang Wu <fengguang.wu@...el.com>
Subject: Re: [PATCH] idr: Document ida tree sections

On Tue, Aug 13, 2013 at 06:44:28PM -0400, Tejun Heo wrote:
> Hello, Kent.
> 
> On Tue, Aug 13, 2013 at 03:27:59PM -0700, Kent Overstreet wrote:
> > It's only naturally a radix tree problem _if_ you require sparseness.
> 
> Well, it's not necessarily about requiring it but more about surviving
> it with some grace when things don't go as expected, which is an
> important characteristic for common library stuff.

The patch I posted should solve the high order allocations stuff, and
sparseness from cyclic allocations was already solved.

> > Otherwise, radix trees require pointer chasing, which we can avoid -
> > which saves us both the cost of chasing pointers (which is significant)
> > and the overhead of storing them.
> 
> Vast majority of which can be avoided with simple caching, right?

Whatever caching optimizations you do with a radix tree version I could
apply to this bitmap tree version, and my bitmap tree code is simpler
and _considerably_ faster than the existing code.
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