On Sat, 2007-02-03 at 09:56 -0800, Christoph Lameter wrote:
> On Sat, 3 Feb 2007, Andrew Morton wrote:
>
> > I wonder if it can be simpler. Make two changes:
>
> Would be great if this could get simpler.
>
> > a) If the scanner encounters an mlocked page on the LRU, take it off.
>
> The current patch takes them off when mlock is set (which may not work
> since the page may be off the LRU) and then has the scanner taking them
> off. We could just remove the early one but what would this bring us?
it's simpler. You only move them off when you encounter them during a
scan. No walking early etc etc. Only do work when there is an actual
situation where you do scan.
>
> > b) munlock() adds all affected pages to the LRU.
>
> Hmmm... You mean without checking all the vmas of a page for VM_LOCKED? So they
> are going to be removed again on the next pass? Ok. I see that makes it
> simpler but it requires another reclaim scan.
Well.. That's the point! Only IF there is a reclaim scan do you move
them out again. The fact that these pages are on the list isn't a
problem. The fact that you keep encountering them over and over again
during *scanning* is. So Andrews suggestion makes them go away in the
situations that actually matter
> The page flag allows a clean state transition of a page and accurate
> keeping of statistics for MLOCKed pages. There were objections against the
> fuzzy counting in the earlier incarnation and it was proposed that a page
> flag be introduced. Without the flag we cannot know that the page is
> already mapped by a VM_LOCKED vma without scanning over all vmas
> referencing the page.
who cares though.. just do it lazy.
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