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    Subject[PATCH RFC] hotplug-memory: refactor online_pages to separate zone growth from page onlining
    The Xen balloon driver needs to separate the process of hot-installing
    memory into two phases: one to allocate the page structures and
    configure the zones, and another to actually online the pages of newly
    installed memory.

    This patch splits up the innards of online_pages() into two pieces which
    correspond to these two phases. The behaviour of online_pages() itself
    is unchanged.

    Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
    Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Cc: Yasunori Goto <y-goto@jp.fujitsu.com>
    Cc: Christoph Lameter <clameter@sgi.com>
    Cc: Dave Hansen <dave@linux.vnet.ibm.com>
    ---
    include/linux/memory_hotplug.h | 3 +
    mm/memory_hotplug.c | 66 ++++++++++++++++++++++++++++++++--------
    2 files changed, 57 insertions(+), 12 deletions(-)

    ===================================================================
    --- a/include/linux/memory_hotplug.h
    +++ b/include/linux/memory_hotplug.h
    @@ -57,7 +57,10 @@
    /* need some defines for these for archs that don't support it */
    extern void online_page(struct page *page);
    /* VM interface that may be used by firmware interface */
    +extern int prepare_online_pages(unsigned long pfn, unsigned long nr_pages);
    +extern unsigned long mark_pages_onlined(unsigned long pfn, unsigned long nr_pages);
    extern int online_pages(unsigned long, unsigned long);
    +
    extern void __offline_isolated_pages(unsigned long, unsigned long);
    extern int offline_pages(unsigned long, unsigned long, unsigned long);

    ===================================================================
    --- a/mm/memory_hotplug.c
    +++ b/mm/memory_hotplug.c
    @@ -180,31 +180,35 @@
    return 0;
    }

    -
    -int online_pages(unsigned long pfn, unsigned long nr_pages)
    +/* Tell anyone who's interested that we're onlining some memory */
    +static int notify_going_online(unsigned long pfn, unsigned long nr_pages)
    {
    - unsigned long flags;
    - unsigned long onlined_pages = 0;
    - struct zone *zone;
    - int need_zonelists_rebuild = 0;
    + struct memory_notify arg;
    int nid;
    int ret;
    - struct memory_notify arg;

    arg.start_pfn = pfn;
    arg.nr_pages = nr_pages;
    arg.status_change_nid = -1;
    -
    +
    nid = page_to_nid(pfn_to_page(pfn));
    if (node_present_pages(nid) == 0)
    arg.status_change_nid = nid;

    ret = memory_notify(MEM_GOING_ONLINE, &arg);
    ret = notifier_to_errno(ret);
    - if (ret) {
    + if (ret)
    memory_notify(MEM_CANCEL_ONLINE, &arg);
    - return ret;
    - }
    +
    + return ret;
    +}
    +
    +/* Grow the zone to fit the expected amount of memory being added */
    +static struct zone *online_pages_zone(unsigned long pfn, unsigned long nr_pages)
    +{
    + struct zone *zone;
    + unsigned long flags;
    +
    /*
    * This doesn't need a lock to do pfn_to_page().
    * The section can't be removed here because of the
    @@ -215,6 +219,16 @@
    grow_zone_span(zone, pfn, pfn + nr_pages);
    grow_pgdat_span(zone->zone_pgdat, pfn, pfn + nr_pages);
    pgdat_resize_unlock(zone->zone_pgdat, &flags);
    +
    + return zone;
    +}
    +
    +/* Mark a set of pages as online */
    +unsigned long mark_pages_onlined(unsigned long pfn, unsigned long nr_pages)
    +{
    + struct zone *zone = page_zone(pfn_to_page(pfn));
    + unsigned long onlined_pages = 0;
    + int need_zonelists_rebuild = 0;

    /*
    * If this zone is not populated, then it is not in zonelist.
    @@ -240,10 +254,38 @@
    vm_total_pages = nr_free_pagecache_pages();
    writeback_set_ratelimit();

    - if (onlined_pages)
    + if (onlined_pages) {
    + struct memory_notify arg;
    +
    + arg.start_pfn = pfn; /* ? */
    + arg.nr_pages = onlined_pages;
    + arg.status_change_nid = -1; /* ? */
    +
    memory_notify(MEM_ONLINE, &arg);
    + }

    + return onlined_pages;
    +}
    +
    +int prepare_online_pages(unsigned long pfn, unsigned long nr_pages)
    +{
    + int ret = notify_going_online(pfn, nr_pages);
    + if (ret)
    + return ret;
    +
    + online_pages_zone(pfn, nr_pages);
    return 0;
    +}
    +
    +int online_pages(unsigned long pfn, unsigned long nr_pages)
    +{
    + int ret;
    +
    + ret = prepare_online_pages(pfn, nr_pages);
    + if (ret == 0)
    + mark_pages_onlined(pfn, nr_pages);
    +
    + return ret;
    }
    #endif /* CONFIG_MEMORY_HOTPLUG_SPARSE */




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