Re: [RFC 4/8] Enhance fallback functions in libs to support higher order pages

[Christoph Lameter <clameter@sgi.com>]

On Fri, 20 Apr 2007, Jens Axboe wrote:

> This works fine as long as you are in the submitter context, but once
> you pass the into the block layer, we don't have any way to find the
> address space (at least we don't want to). Would something like this be
> workable, name withstanding:
> 
> static unsigned long page_size(struct page *page)
> {
>         struct address_space *mapping;
>         int order = 0;
> 
>         mapping = page_mapping(page);
>         if (mapping)
>                 order = mapping->order;
> 
>         return PAGE_CACHE_SIZE << order;
> }

There is much simpler solution (possible with mm)

PAGE_SIZE << compound_order(page)

compound_order will return 0 for a non compound page.

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