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    SubjectRe: [PATCH 1/2] mm: hotplug: implement non-movable version of get_user_pages() called get_user_pages_non_movable()
    Hi Mel,

    On 02/18/2013 11:17 PM, Mel Gorman wrote:
    >>> > > <SNIP>
    >>> > >
    >>> > > result. It's a little clumsy but the memory hot-remove failure message
    >>> > > could list what applications have pinned the pages that cannot be removed
    >>> > > so the administrator has the option of force-killing the application. It
    >>> > > is possible to discover what application is pinning a page from userspace
    >>> > > but it would involve an expensive search with /proc/kpagemap
    >>> > >
    >>>>> > >>> + if (migrate_pre_flag && !isolate_err) {
    >>>>> > >>> + ret = migrate_pages(&pagelist, alloc_migrate_target, 1,
    >>>>> > >>> + false, MIGRATE_SYNC, MR_SYSCALL);
    >>> > >
    >>> > > The conversion of alloc_migrate_target is a bit problematic. It strips
    >>> > > the __GFP_MOVABLE flag and the consequence of this is that it converts
    >>> > > those allocation requests to MIGRATE_UNMOVABLE. This potentially is a large
    >>> > > number of pages, particularly if the number of get_user_pages_non_movable()
    >>> > > increases for short-lived pins like direct IO.
    >> >
    >> > Sorry, I don't quite understand here neither. If we use the following new
    >> > migration allocation function as you said, the increasing number of
    >> > get_user_pages_non_movable() will also lead to large numbers of MIGRATE_UNMOVABLE
    >> > pages. What's the difference, do I miss something?
    >> >
    > The replacement function preserves the __GFP_MOVABLE flag. It cannot use
    > ZONE_MOVABLE but otherwise the newly allocated page will be grouped with
    > other movable pages.

    Ah, got it " But GFP_MOVABLE is not only a zone specifier but also an allocation policy.".

    Could I clear __GFP_HIGHMEM flag in alloc_migrate_target depending on private parameter so
    that we can keep MIGRATE_UNMOVABLE policy also allocate page none movable zones with little
    change?

    Does that approach work? Otherwise I have to follow your suggestion.

    thanks,
    linfeng


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