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    SubjectRe: [RFC 1/2] deactive invalidated pages
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    On Wed, Nov 24, 2010 at 7:10 AM, Mel Gorman <mel@csn.ul.ie> wrote:
    > On Tue, Nov 23, 2010 at 12:35:35PM -0800, Andrew Morton wrote:
    >> On Tue, 23 Nov 2010 14:58:56 +0000
    >> Mel Gorman <mel@csn.ul.ie> wrote:
    >>
    >> > On Tue, Nov 23, 2010 at 09:55:49AM -0500, Ben Gamari wrote:
    >> > > On Tue, 23 Nov 2010 09:38:59 +0000, Mel Gorman <mel@csn.ul.ie> wrote:
    >> > > > > If it's mapped pagecache then the user was being a bit silly (or didn't
    >> > > > > know that some other process had mapped the file).  In which case we
    >> > > > > need to decide what to do - leave the page alone, deactivate it, or
    >> > > > > half-deactivate it as this patch does.
    >> > > > >
    >> > > >
    >> > > > What are the odds of an fadvise() user having used mincore() in advance
    >> > > > to determine if the page was in use by another process? I would guess
    >> > > > "low" so this half-deactivate gives a chance for the page to be promoted
    >> > > > again as well as a chance for the flusher threads to clean the page if
    >> > > > it really is to be reclaimed.
    >> > > >
    >> > > Do we really want to make the user jump through such hoops as using
    >> > > mincore() just to get the kernel to handle use-once pages properly?
    >> >
    >> > I would think "no" which is why I support half-deactivating pages so they won't
    >> > have to.
    >>
    >> If the page is page_mapped() then we can assume that some other process
    >> is using it and we leave it alone *altogether*.
    >>
    >
    > Agreed, that makes perfect sense.
    >
    >> If the page is dirty or under writeback (and !page_mapped()) then we
    >> should assume that we should free it asap.  The PageReclaim() trick
    >> might help with that.
    >>
    >
    > Again agreed.
    >
    >> I just don't see any argument for moving the page to the head of the
    >> inactive LRU as a matter of policy.  We can park it there because we
    >> can't think of anythnig else to do with it, but it's the wrong place
    >> for it.
    >>
    >
    > Is there a better alternative? One thing that springs to mind is that we are
    > not exactly tracking very well what effect these policy changes have. The
    > analysis scripts I have do a reasonable job on tracking reclaim activity
    > (although only as part of the mmtests tarball, I should split them out as
    > a standalone tool) but not the impact - namely minor and major faults. I
    > should sort that out so we can put better reclaim analysis in place.

    It can help very much. :)

    Also, I need time since I am so busy.

    >
    > --
    > Mel Gorman
    > Part-time Phd Student                          Linux Technology Center
    > University of Limerick                         IBM Dublin Software Lab
    >



    --
    Kind regards,
    Minchan Kim
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