Re: page flags ?

[Badari Pulavarty <pbadari@us.ibm.com>]

On Wed, 2005-05-18 at 16:23, Andrew Morton wrote:
> Badari Pulavarty <pbadari@us.ibm.com> wrote:
> >
> > Is it possible to get yet another PG_fs_specific flag ? 
> 
> Anything's possible ;)
> 
> How many bits are spare now?  ZONETABLE_PGSHIFT hurts my brain.

Depends on whom you ask :) CKRM folks are using one/few, 
Hotplug memory guys are using one... :( I lost track..

> 
> > Reasons for it are:
> > 
> > 	- I need this for supporting delayed allocation on ext3.
> 
> Why?
> 

I think, I explained you earlier.. But let me refresh your memory.


In order to do delayed allocation, we "reserve" (not same reservation
the code) a block in prepare/commit and do the allocation in
writepage/writepages.  Unfortunately, mapped writes directly come into
writepage without making a reservation. In order to guarantee that
write() succeeds, I need a way to indicate if the "page" has made
a reservation or not. I was hoping to use a page->flag to do this.
That way I don't have to touch page->private like Alex's code and
get away using mpage routines, instead of having my own.


Thanks,
Badari


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