Re: [patch 8/8] Pageflags: Eliminate PG_xxx aliases

[Christoph Lameter <clameter@sgi.com>]

On Fri, 7 Mar 2008, Nick Piggin wrote:

> > It avoids us having to deal with aliases in the future.
> 
> It doesn't. You still have to deal with them.

Sortof.

You do not have to deal with it on the level of the PG_xxx enum constant. 
Yes you will have to deal with the aliases at the level of the 
functions.

> > PG_xx at this 
> > point is not unique which can be confusing. See the PG_reclaim in
> > mm/page_alloc.c. It also means PG_readahead. If I look for
> > handling of PG_readahead then I wont find it.
> 
> You can't just pretend not to deal with aliases at that point
> in mm/page_alloc.c just becuase you only have one name for the
> bit position.

If you only have one name for the bit position the you can localize the 
aliases and uses of that bit. This means you can go from a bit that you 
see set while debugging to the PG_xxx flag and then look for uses. Which 
will turn up aliases.

> You still have to know that checking for PG_reclaim in bad_page
> can only be done if it is *also* a bug for PG_readahead to be
> found set at that point too. Because it is an alias.

True.

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