Date: Sat, 3 Apr 2004 15:46:08 -0800
From: Andrew Morton <akpm@osdl.org>
To: Andrea Arcangeli <andrea@suse.de>
Cc: hch@infradead.org, hugh@veritas.com, vrajesh@umich.edu,
       linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [RFC][PATCH 1/3] radix priority search tree - objrmap
 complexity fix
Message-Id: <20040403154608.78e98877.akpm@osdl.org>
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Andrea Arcangeli <andrea@suse.de> wrote:
>
> On Sat, Apr 03, 2004 at 12:02:27PM -0800, Andrew Morton wrote:
> > It might be better to switch over to address masking in get_user_pages()
> > and just dump all the compound page logic.  I don't immediately see how the
> 
> I'm all for it, this is how the 2.4 get_user_pages deals with bigpages
> too, I've never enjoyed the compound thing.
> 
> > get_user_pages() caller can subsequently do put_page() against the correct
> > pageframe, but I assume you worked that out?
> 
> see this patch:
> 
> 	http://www.us.kernel.org/pub/linux/kernel/people/andrea/kernels/v2.4/2.4.23aa2/9910_shm-largepage-18.gz
> 
> it's a two liner fix in follow_page:
> 
> @@ -439,6 +457,8 @@ static struct page * follow_page(struct
>         pmd = pmd_offset(pgd, address);
>         if (pmd_none(*pmd))
>                 goto out;
> +       if (pmd_bigpage(*pmd))
> +               return __pmd_page(*pmd) + (address & BIGPAGE_MASK) / PAGE_SIZE;

OK, that's an x86 solution.  But this addresses the easy part - the messy
part happens where we want to unpin the pages at I/O completion in
bio_release_pages() when the page may not even be in a vma any more..


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