From: Rik van Riel [mailto:riel@redhat.com]
Subject: Re: [PATCH] mm: implement WasActive page flag (for improving cleancache)

On 01/26/2012 09:43 PM, Dan Magenheimer wrote:

quoted

Maybe the Active page bit could be overloaded with some minor
rewriting?  IOW, perhaps the Active bit could be ignored when
the page is moved to the inactive LRU?  (Confusing I know, but I am
just brainstorming...)

The PG_referenced bit is already overloaded.  We keep
the bit set when we move a page from the active to the
inactive list, so a page that was previously active
only needs to be referenced once to become active again.

The LRU bits (PG_lru, PG_active, etc) are needed to
figure out which LRU list the page is on.  I don't
think we can overload those...

I suspected that was true, but was just brainstorming.
Thanks for confirming.

Are there any other page bits that are dont-care when
a page is on an LRU list?

I'd also be interested in your/RedHat's opinion on the
64-bit vs 32-bit market.  Will RHEL7 even support 32-bit?

Dan

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