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    SubjectRe: [PATCH v1 4/4] mm/memory_hotplug: online_pages cannot be 0 in online_pages()
    On Fri 09-08-19 14:57:01, David Hildenbrand wrote:
    > walk_system_ram_range() will fail with -EINVAL in case
    > online_pages_range() was never called (== no resource applicable in the
    > range). Otherwise, we will always call online_pages_range() with
    > nr_pages > 0 and, therefore, have online_pages > 0.

    I have no idea why those checks where there TBH. Tried to dig out
    commits which added them but didn't help.

    > Remove that special handling.
    >
    > Cc: Andrew Morton <akpm@linux-foundation.org>
    > Cc: Oscar Salvador <osalvador@suse.de>
    > Cc: Michal Hocko <mhocko@suse.com>
    > Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
    > Cc: Dan Williams <dan.j.williams@intel.com>
    > Signed-off-by: David Hildenbrand <david@redhat.com>

    Acked-by: Michal Hocko <mhocko@suse.com>

    > ---
    > mm/memory_hotplug.c | 22 +++++++++-------------
    > 1 file changed, 9 insertions(+), 13 deletions(-)
    >
    > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
    > index 87f85597a19e..07e72fe17495 100644
    > --- a/mm/memory_hotplug.c
    > +++ b/mm/memory_hotplug.c
    > @@ -854,6 +854,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
    > ret = walk_system_ram_range(pfn, nr_pages, &onlined_pages,
    > online_pages_range);
    > if (ret) {
    > + /* not a single memory resource was applicable */
    > if (need_zonelists_rebuild)
    > zone_pcp_reset(zone);
    > goto failed_addition;
    > @@ -867,27 +868,22 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
    >
    > shuffle_zone(zone);
    >
    > - if (onlined_pages) {
    > - node_states_set_node(nid, &arg);
    > - if (need_zonelists_rebuild)
    > - build_all_zonelists(NULL);
    > - else
    > - zone_pcp_update(zone);
    > - }
    > + node_states_set_node(nid, &arg);
    > + if (need_zonelists_rebuild)
    > + build_all_zonelists(NULL);
    > + else
    > + zone_pcp_update(zone);
    >
    > init_per_zone_wmark_min();
    >
    > - if (onlined_pages) {
    > - kswapd_run(nid);
    > - kcompactd_run(nid);
    > - }
    > + kswapd_run(nid);
    > + kcompactd_run(nid);
    >
    > vm_total_pages = nr_free_pagecache_pages();
    >
    > writeback_set_ratelimit();
    >
    > - if (onlined_pages)
    > - memory_notify(MEM_ONLINE, &arg);
    > + memory_notify(MEM_ONLINE, &arg);
    > mem_hotplug_done();
    > return 0;
    >
    > --
    > 2.21.0

    --
    Michal Hocko
    SUSE Labs

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