Subject: Re: uvm & flushing
To: Jason Thorpe <>
From: Chuck Silvers <>
List: tech-kern
Date: 12/14/1999 16:56:38
yes, you can go count the dirty pages anytime you want to know,
but you can't maintain a count over time.

at any rate, it's not worth messing around too much with this
since it'll all change in a couple months anyway.  it'll be much
nicer then.


On Tue, Dec 14, 1999 at 04:42:46PM -0800, Jason Thorpe wrote:
> On Tue, 14 Dec 1999 16:35:42 -0800 
>  Chuck Silvers <> wrote:
>  > the count of dirty pages is only possible if you know that no pages are
>  > mapped.  mapped pages can become dirty without the kernel being notified.
>  > the concept doesn't really work very well.
> Not if you write-protect the pages... like a COW-type thing, except it
> doesn't cause a COW to happen, just for the pages to be marked dirty.
> However, this could have bad interactions with wired pages.  Sigh.
> Another option would be to use pmap_is_modified() ... flushing the pages
> before the archive process begins will clear the modified attribute, and
> you could just lock the object and check all the pages again after the
> archive process completes... This should work, since pmap_is_modified()
> *has* to work in order for the VM system to function properly.
>         -- Jason R. Thorpe <>