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    SubjectRe: [PATCH] switch free memory back to MIGRATE_MOVABLE
    On Mon, 13 Jul 2009 11:18:01 +0800
    Shaohua Li <shaohua.li@intel.com> wrote:

    > On Mon, Jul 13, 2009 at 11:08:14AM +0800, KOSAKI Motohiro wrote:
    > > > On Mon, Jul 13, 2009 at 10:58:03AM +0800, KAMEZAWA Hiroyuki wrote:
    > > > > On Mon, 13 Jul 2009 11:47:46 +0900 (JST)
    > > > > KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
    > > > >
    > > > > > > When page is back to buddy and its order is bigger than pageblock_order, we can
    > > > > > > switch its type to MIGRATE_MOVABLE. This can reduce fragmentation. The patch
    > > > > > > has obvious effect when read a block device and then drop caches.
    > > > > > >
    > > > > > > Signed-off-by: Shaohua Li <shaohua.li@intel.com>
    > > > > >
    > > > > > This patch change hot path, but there is no performance mesurement description.
    > > > > > Also, I don't like modification buddy core for only drop caches.
    > > > > >
    > > > > Li, does this patch imply fallback of migration type doesn't work well ?
    > > > > What is the bad case ?
    > > > The page is initialized as migrate_movable, and then switch to reclaimable or
    > > > something else when fallback occurs, but its type remains even the page gets
    > > > freed. When the page gets freed, its type actually can be switch back to movable,
    > > > this is what the patch does.
    > >
    > > This answer is not actual answer.
    > > Why do you think __rmqueue_fallback() doesn't works well? Do you have
    > > any test-case or found a bug by review?
    > I never said __rmqueue_fallback() doesn't work well. The page is already freed, switching
    > back the pageblock to movable might make next page allocation (non-movable) skip this
    > pageblock. So this could potentially reduce fragmentation and improve memory offline.
    > But your guys are right, I have no number if this will impact performance.
    >
    If this is for memory offlining, plz mention that at first ;)
    IIUC, if this can be a problem, fixing memory offline itself is better. No ?
    At implementing memory unplug, I had no problems because I assumes ZONE_MOVABLE.
    But ok, I welcome enhances to memory unplug.

    If this part is bad for you.
    4714 /*
    4715 * In future, more migrate types will be able to be isolation target.
    4716 */
    4717 if (get_pageblock_migratetype(page) != MIGRATE_MOVABLE)
    4718 goto out;

    plz fix this to do more precise work for zid != ZONE_MOVABLE zones.
    As I wrote in comments. My codes assumes ZONE_MOVABLE in many parts because I want
    100%-success memory offline.

    Thanks,
    -Kame



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