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    SubjectRe: [patch 00/23] Slab defragmentation V6
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    On Thu, 2007-11-08 at 11:12 -0800, Christoph Lameter wrote:
    > On Thu, 8 Nov 2007, Mel Gorman wrote:
    >
    > > On Tue, 2007-11-06 at 17:11 -0800, Christoph Lameter wrote:
    > > > Slab defragmentation is mainly an issue if Linux is used as a fileserver
    > >
    > > Was hoping this would get renamed to SLUB Targetted Reclaim from
    > > discussions at VM Summit. As no copying is taking place, it's confusing
    > > to call it defragmentation to me anyway. Not a major deal but it made
    > > reading the patches a little confusing.
    >
    > The problem is that people are focusing on one feature here and forget
    > about the rest. Targetted reclaim is one feature that was added later when
    > lumpy reclaim was added to the kernel. The primary intend of this patchset
    > was always to reduce the fragmentation. The name is appropriate and the
    > patchset will support copying of objects as soon as support for that is
    > added to the kick(). In that case the copying you are looking for will be
    > there. The simple implementation for the kick() methods is to simply copy
    > pieces of the reclaim code. That is what is included here.
    >
    > > > With lumpy reclaim slab defragmentation can be used to enhance the
    > > > ability to recover larger contiguous areas of memory. Lumpy reclaim currently
    > > > cannot do anything if a slab page is encountered. With slab defragmentation
    > > > that slab page can be removed and a large contiguous page freed. It may
    > > > be possible to have slab pages also part of ZONE_MOVABLE (Mel's defrag
    > > > scheme in 2.6.23)
    > >
    > > More terminology nit-pick - ZONE_MOVABLE is not defragmenting anything.
    > > It's just partitioning memory. The slab pages need to be 100%
    > > reclaimable or movable for that to happen but even with targetted
    > > reclaim, some dentries such as the root directory one cannot be
    > > reclaimed, right?
    >
    > 100%? I am so fond of these categorical statements ....
    >
    > ZONE_MOVABLE also contains mlocked pages that are also not reclaimable.
    > The question is at what level would it be possible to make them MOVABLE?
    > It may take some improvements to the kick() methods to make eviction more
    > reliable. Allowing the moving of objects in the kick() methods will
    > likely get usthere.

    Christoph: Although mlocked pages are not reclaimable, they ARE
    migratable. You fixed that a long time ago. [And I just verified with
    memtoy.] Doesn't this make them "movable"?

    Lee

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