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    SubjectRE: [PATCH] mm: implement WasActive page flag (for improving cleancache)
    > From: Dave Hansen [mailto:dave@linux.vnet.ibm.com]
    > Subject: Re: [PATCH] mm: implement WasActive page flag (for improving cleancache)

    Thanks for the review Dave!

    > 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.

    No, there are no changes in cleancache.c so it isn't clearing
    the bit.

    > 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?

    True, it is not getting cleared and it should be, good catch!

    I'll find the place to add the call to ClearPageWasActive() for v2.

    Thanks,
    Dan



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