Re: [PATCH 2/5] hugetlb: Fix quota management for private mappings

[Adam Litke <agl@us.ibm.com>]

On Tue, 2007-10-30 at 16:28 -0700, Christoph Lameter wrote:
> On Tue, 30 Oct 2007, Andrew Morton wrote:
> 
> > > This patch (based on a prototype provided by Ken Chen) moves quota
> > > crediting for all pages into free_huge_page().  page->private is used to
> > > store a pointer to the mapping to which this page belongs.  This is used to
> > > credit quota on the appropriate hugetlbfs instance.
> > > 
> > 
> > Consuming page.private on hugetlb pages is a noteworthy change.  I'm in
> > fact surprised that it's still available.
> > 
> > I'd expect that others (eg Christoph?) have designs upon it as well.  We
> > need to work out if this is the best use we can put it to.
> 
> The private pointer in the first page of a compound page is always 
> available. However, why do we not use page->mapping for that purpose? 
> Could we stay as close as possible to regular page cache field use?

We could use page->mapping, but add_to_page_cache() already fills it in
for shared huge pages.  Even though add_to_page_cache and
alloc_huge_page would be storing the same value there, it seems a bit
odd to double-assign it.

-- 
Adam Litke - (agl at us.ibm.com)
IBM Linux Technology Center

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