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    SubjectRe: [RFC][PATCH] mm: remove unnecessary loop inside shrink_inactive_list()
    On Fri, Aug 21, 2009 at 07:09:17PM +0800, KOSAKI Motohiro wrote:
    > 2009/8/20 Wu Fengguang <fengguang.wu@intel.com>:
    > > shrink_inactive_list() won't be called to scan too much pages
    > > (unless in hibernation code which is fine) or too few pages (ie.
    > > batching is taken care of by the callers).  So we can just remove the
    > > big loop and isolate the exact number of pages requested.
    > >
    > > Just a RFC, and a scratch patch to show the basic idea.
    > > Please kindly NAK quick if you don't like it ;)
    >
    > Hm, I think this patch taks only cleanups. right?
    > if so, I don't find any objection reason.

    Mostly cleanups, but one behavior change here:

    > > -               nr_taken = sc->isolate_pages(sc->swap_cluster_max,
    > > +               nr_taken = sc->isolate_pages(nr_to_scan,
    > >                             &page_list, &nr_scan, sc->order, mode,
    > >                                zone, sc->mem_cgroup, 0, file);

    The new behavior is to scan exactly the number of pages that
    shrink_zone() or other callers tell it. It won't try to "round it up"
    to 32 pages. This new behavior is in line with shrink_active_list()'s
    current status as well as shrink_zone()'s expectation.

    shrink_zone() may still submit scan requests for <32 pages, which is
    suboptimal. I'll try to eliminate that totally with more patches.

    > >                nr_active = clear_active_flags(&page_list, count);
    > > @@ -1093,7 +1095,6 @@ static unsigned long shrink_inactive_lis
    > >
    > >                spin_unlock_irq(&zone->lru_lock);
    > >
    > > -               nr_scanned += nr_scan;
    > >                nr_freed = shrink_page_list(&page_list, sc, PAGEOUT_IO_ASYNC);
    > >
    > >                /*
    > > @@ -1117,7 +1118,7 @@ static unsigned long shrink_inactive_lis
    > >                                                        PAGEOUT_IO_SYNC);
    > >                }
    > >
    > > -               nr_reclaimed += nr_freed;
    > > +               nr_reclaimed = nr_freed;
    >
    > maybe, nr_freed can be removed perfectly. it have the same meaning as
    > nr_reclaimed.

    Yes, good spot!

    Thanks,
    Fengguang
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