Re: [RFC PATCH 0/2] mm: Add ability to monitor task's memory changes

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On Tue, 04 Dec 2012 18:17:08 -0600
Matt Mackall <mpm@xxxxxxxxxxx> wrote:

> On Tue, 2012-12-04 at 15:21 -0800, Andrew Morton wrote:
> > On Tue, 04 Dec 2012 09:15:10 +0400
> > Pavel Emelyanov <xemul@xxxxxxxxxxxxx> wrote:
> > 
> > > 
> > > > Two alternatives come to mind:
> > > > 
> > > > 1)  Use /proc/pid/pagemap (Documentation/vm/pagemap.txt) in some
> > > >     fashion to determine which pages have been touched.
> 
> [momentarily coming out of kernel retirement for old man rant]
> 
> This is a popular interface anti-pattern.
> 
> You shouldn't use an interface that gives you huge amount of STATE to
> detect small amounts of CHANGE via manual differentiation.

I'm not sure that's what checkpoint-restart will be doing.  If we want
to determine "which pages have been touched since the last checkpoint
ten minutes ago" then that set of touched pages *is* state.  And it's
not "small"!


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