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

From: Linus Torvalds
Date: Thu Mar 16 2006 - 15:32:55 EST

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.

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