Re: Is get_user_pages() enough to prevent pages from being swappedout ?

[Hugh Dickins]

On Thu, 30 Jul 2009, Robin Holt wrote:
> > > On Wednesday 29 July 2009 17:26:11 Hugh Dickins wrote:
> ...
> > > > On the other hand, despite the raised reference count, under memory
> > > > pressure that page might get unmapped from the user pagetable, and
> > > > might even be written out to swap in its half-dirty state (though
> 
> One thing you did not mention in the above description is that the page
> is marked clean by the write-out to swap.  I am not sure I recall the
> method of mapping involved here, but it is necessary to ensure the page
> is marked dirty again before the driver releases it.  If the page is
> not marked dirty as part of your method of releasing it, the changes
> you have made between when the page was first written out and when you
> are freeing it will get lost.

Yes indeed: thanks, Robin.

Hugh
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