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Date: Thu, 12 Sep 2002 15:51:24 -0700
From: Andrew Morton <akpm@digeo.com>
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To: Rik van Riel <riel@conectiva.com.br>
CC: Urban Widmark <urban@teststation.com>, Chuck Lever <cel@citi.umich.edu>,
       Daniel Phillips <phillips@arcor.de>, trond.myklebust@fys.uio.no,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: invalidate_inode_pages in 2.5.32/3
References: <3D811363.70ABB50C@digeo.com> <Pine.LNX.4.44L.0209121926310.1857-100000@imladris.surriel.com>
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Rik van Riel wrote:
> 
> On Thu, 12 Sep 2002, Andrew Morton wrote:
> 
> > Well the lazy invalidation would be OK - defer that to the next
> > userspace access,
> 
> I think I have an idea on how to do that, here's some pseudocode:
> 
> invalidate_page(struct page * page) {
>         SetPageInvalidated(page);
>         rmap_lock(page);
>         for_each_pte(pte, page) {
>                 make pte PROT_NONE;
>                 flush TLBs for this virtual address;
>         }
>         rmap_unlock(page);
> }
> 
> And in the page fault path:
> 
> if (pte_protection(pte) == PROT_NONE && PageInvalidated(pte_page_pte)) {
>         clear_pte(ptep);
>         page_cache_release(page);
>         mm->rss--;
> }
> 

That's the bottom-up approach.  The top-down (vmtruncate) approach
would also work, if the locking is suitable.

Look, idunnoigiveup.  Like scsi and USB, NFS is a black hole
where akpms fear to tread.  I think I'll sulk until someone
explains why this work has to be performed in the context of
a process which cannot do it.
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