Re: [PATCH 10 of 20] ipath - support for userspace apps using core driver

[Linus Torvalds <torvalds@osdl.org>]

On Thu, 16 Mar 2006, Hugh Dickins wrote:

> On Thu, 16 Mar 2006, Bryan O'Sullivan wrote:
> > 
> > OK.  Would it be correct to say that this is what we should do, then?
> > 
> >       * On 2.6.15 and later kernels, use __GFP_COMP at allocation time,
> >         and get_page in ->nopage.  This is what we're doing as of this
> >         morning, and it works.
> >       * For backports to 2.6.14 and earlier, avoid __GFP_COMP, mark each
> >         page with SetPageReserved at allocation time, and do nothing
> >         special in ->nopage.  Do we need to ClearPageReserved before
> >         freeing?
> 
> Yes, I believe that's exactly right - so long as you do ClearPageReserved
> from each of its constituent 0-order-pages before freeing the >0-order
> page, in the <= 2.6.14 case.

The alternative is to always allocate the pages one by one ("order-0"), 
and do get_page() when you return them in the ->nopage handler. That will 
work with any kernel, so it has the simplicity thing going for it.

		Linus
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