Wu Fengguang writes:
> On Sun, Dec 04, 2005 at 06:03:15PM +0300, Nikita Danilov wrote:
> > > inter-reference distance, and therefore should be better protected(if ignore
> > > possible read-ahead effects). If we move re-accessed pages immediately into
> > > active_list, we are pushing them closer to danger of eviction.
> >
> > Huh? Pages in the active list are closer to the eviction? If it is
> > really so, then CLOCK-pro hijacks the meaning of active list in a very
> > unintuitive way. In the current MM active list is supposed to contain
> > hot pages that will be evicted last.
>
> The page is going to active list anyway. So its remaining lifetime in inactive
> list is killed by the early move.
But this change increased lifetimes of _all_ pages, so this is
irrelevant. Consequently, it has a chance of increasing scanning
activity, because there will be more referenced pages at the cold tail
of the inactive list.
And --again-- this erases information about relative order of
references, and this is important. In the past, several VM modifications
(like split inactive_clean and inactive_dirty lists) were tried that had
various advantages over current scanner, but maintained weaker LRU, and
they all were found to degrade horribly under certain easy triggerable
conditions.
>
> Thanks,
> Wu
Nikita.
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