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    SubjectRe: [RFC 6/8] In order putback lru core
    On Wed, 27 Apr 2011 01:25:23 +0900
    Minchan Kim <> wrote:

    > This patch defines new APIs to putback the page into previous position of LRU.
    > The idea is simple.
    > When we try to putback the page into lru list and if friends(prev, next) of the pages
    > still is nearest neighbor, we can insert isolated page into prev's next instead of
    > head of LRU list. So it keeps LRU history without losing the LRU information.
    > Before :
    > LRU POV : H - P1 - P2 - P3 - P4 -T
    > Isolate P3 :
    > LRU POV : H - P1 - P2 - P4 - T
    > Putback P3 :
    > if (P2->next == P4)
    > putback(P3, P2);
    > So,
    > LRU POV : H - P1 - P2 - P3 - P4 -T
    > For implement, we defines new structure pages_lru which remebers
    > both lru friend pages of isolated one and handling functions.
    > But this approach has a problem on contiguous pages.
    > In this case, my idea can not work since friend pages are isolated, too.
    > It means prev_page->next == next_page always is false and both pages are not
    > LRU any more at that time. It's pointed out by Rik at LSF/MM summit.
    > So for solving the problem, I can change the idea.
    > I think we don't need both friend(prev, next) pages relation but
    > just consider either prev or next page that it is still same LRU.
    > Worset case in this approach, prev or next page is free and allocate new
    > so it's in head of LRU and our isolated page is located on next of head.
    > But it's almost same situation with current problem. So it doesn't make worse
    > than now and it would be rare. But in this version, I implement based on idea
    > discussed at LSF/MM. If my new idea makes sense, I will change it.

    I think using only 'next'(prev?) pointer will be enough.


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