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    SubjectRe: [PATCH 8/8] writeback: Do not sleep on the congestion queue if there are no congested BDIs or if significant congestion is not being encountered in the current zone
    > > > <snip>
    > > >
    > > > > struct scan_control *sc)
    > > > > {
    > > > > + enum bdi_queue_status ret = QUEUEWRITE_DENIED;
    > > > > +
    > > > > if (current->flags & PF_SWAPWRITE)
    > > > > - return 1;
    > > > > + return QUEUEWRITE_ALLOWED;
    > > > > if (!bdi_write_congested(bdi))
    > > > > - return 1;
    > > > > + return QUEUEWRITE_ALLOWED;
    > > > > + else
    > > > > + ret = QUEUEWRITE_CONGESTED;
    > > > > if (bdi == current->backing_dev_info)
    > > > > - return 1;
    > > > > + return QUEUEWRITE_ALLOWED;
    > > > >
    > > > > /* lumpy reclaim for hugepage often need a lot of write */
    > > > > if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
    > > > > - return 1;
    > > > > - return 0;
    > > > > + return QUEUEWRITE_ALLOWED;
    > > > > + return ret;
    > > > > }
    > > >
    > > > The function can't return QUEUEXXX_DENIED.
    > > > It can affect disable_lumpy_reclaim.
    > > >
    > >
    > > Yes, but that change was made in "vmscan: Narrow the scenarios lumpy
    > > reclaim uses synchrounous reclaim". Maybe I am misunderstanding your
    > > objection.
    >
    > I means current may_write_to_queue never returns QUEUEWRITE_DENIED.
    > What's the role of it?
    >

    As of now, little point because QUEUEWRITE_CONGESTED implies denied. I was allowing
    the possibility of distinguishing between these cases in the future depending
    on what happened with wait_iff_congested(). I will drop it for simplicity
    and reintroduce it when or if there is a distinction between
    denied and congested.

    > In addition, we don't need disable_lumpy_reclaim_mode() in pageout.
    > That's because both PAGE_KEEP and PAGE_KEEP_CONGESTED go to keep_locked
    > and calls disable_lumpy_reclaim_mode at last.
    >

    True, good spot.

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


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