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SubjectRe: [PATCH] mm: implement WasActive page flag (for improving cleancache)
On 01/25/2012 01:58 PM, Dan Magenheimer wrote:
> (Feedback welcome if there is a different/better way to do this
> without using a page flag!)
>
> Since about 2.6.27, the page replacement algorithm maintains
> an "active" bit to help decide which pages are most eligible
> to reclaim, see http://linux-mm.org/PageReplacementDesign
>
> This "active' information is also useful to cleancache but is lost
> by the time that cleancache has the opportunity to preserve the
> pageful of data. This patch adds a new page flag "WasActive" to
> retain the state. The flag may possibly be useful elsewhere.

I guess cleancache itself is clearing the bit, right? I didn't see any
clearing going on in the patch.

I do think it also needs to get cleared on the way in to the page
allocator. Otherwise:

PageSetWasActive(page);
free_page(page);
...
another_user_page = get_free_page()
// now cleancache sees the active bit for the prev user

Or am I missing somewhere it gets cleared non-explicitly somewhere?



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