Re: [rfc][patch 2/2] mm: mlocked pages off LRU

[Christoph Lameter <clameter@sgi.com>]

On Tue, 6 Mar 2007, Nick Piggin wrote:

> > > > I think there is still some thinking going on about also removing 
> > > > anonymous pages off the LRU if we are out of swap or have no swap. In 
> > > > that case we may need page->lru to track these pages so that they can be 
> > > > fed back to the LRU when swap is added later.
> > > 
> > > That's OK: they won't get mlocked if they are not on the LRU (and won't
> > > get taken off the LRU if they are mlocked).
> > 
> > But we may want to keep them off the LRU.
> 
> They will be. Either by mlock or by the !swap condition.

The above is a bit contradictory. Assuming they are taken off the LRU:
How will they be returned to the LRU?

> > Wrong. !PageLRU means that the page may be on some other list. Like the 
> > vmscan pagelist and the page migration list. You can only be sure that it
> > is not on those lists if a function took the page off the LRU. If you then 
> > mark it PageMlocked then you may be sure that the LRU field is free for 
> > use.
> 
> Bad wording: by "if we ensure !PageLRU" I meant "if we take the page off
> the LRU ourselves". Why do you have a bad feeling about this? As you
> say, vmscan and page migration do exactly the same thing and it is a
> fundamental way that the lru mechanism works.

Refcounts are generally there to be updated in a racy way and it seems 
here that the refcount variable itself can only exist under certain 
conditions. If you can handle that cleanly then we are okay.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>