Re: [PATCH 0/3] explicitly document overloaded page flags

[Christoph Lameter <clameter@sgi.com>]

On Thu, 15 May 2008, Andy Whitcroft wrote:

> With the recent page flag reorganisation we have a single enum which
> defines the valid page flags and their values, nice and clear.  However
> there are a number of bits which are overloaded by different subsystems.
> Firstly there is PG_owner_priv_1 which is used by filesystems and by XEN.
> Secondly both SLOB and SLUB use a couple of extra page bits to manage
> internal state for pages they own; both overlay other bits.  All of these
> "aliases" are scattered about the source making it very hard for a reader
> to know if the bits are safe to rely on in all contexts; confusion here
> is bad.
> 
> As we now have a single place where the bits are clearly assigned it makes
> sense to clarify the reuse of bits by making the aliases explicit and
> visible with the original bit assignments.  This patch creates explicit
> aliases within the enum itself for the overloaded bits and uses those
> aliases throughout.

Ahh. Great! I considered doing that work too but never got around to it.

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