• Qian Cai's avatar
    mm/hotplug: fix offline undo_isolate_page_range() · 9b7ea46a
    Qian Cai authored
    Commit f1dd2cd1 ("mm, memory_hotplug: do not associate hotadded
    memory to zones until online") introduced move_pfn_range_to_zone() which
    calls memmap_init_zone() during onlining a memory block.
    memmap_init_zone() will reset pagetype flags and makes migrate type to
    be MOVABLE.
    
    However, in __offline_pages(), it also call undo_isolate_page_range()
    after offline_isolated_pages() to do the same thing.  Due to commit
    2ce13640 ("mm: __first_valid_page skip over offline pages") changed
    __first_valid_page() to skip offline pages, undo_isolate_page_range()
    here just waste CPU cycles looping around the offlining PFN range while
    doing nothing, because __first_valid_page() will return NULL as
    offline_isolated_pages() has already marked all memory sections within
    the pfn range as offline via offline_mem_sections().
    
    Also, after calling the "useless" undo_isolate_page_range() here, it
    reaches the point of no returning by notifying MEM_OFFLINE.  Those pages
    will be marked as MIGRATE_MOVABLE again once onlining.  The only thing
    left to do is to decrease the number of isolated pageblocks zone counter
    which would make some paths of the page allocation slower that the above
    commit introduced.
    
    Even if alloc_contig_range() can be used to isolate 16GB-hugetlb pages
    on ppc64, an "int" should still be enough to represent the number of
    pageblocks there.  Fix an incorrect comment along the way.
    
    [cai@lca.pw: v4]
      Link: http://lkml.kernel.org/r/20190314150641.59358-1-cai@lca.pw
    Link: http://lkml.kernel.org/r/20190313143133.46200-1-cai@lca.pw
    Fixes: 2ce13640 ("mm: __first_valid_page skip over offline pages")
    Signed-off-by: default avatarQian Cai <cai@lca.pw>
    Acked-by: default avatarMichal Hocko <mhocko@suse.com>
    Reviewed-by: default avatarOscar Salvador <osalvador@suse.de>
    Cc: Vlastimil Babka <vbabka@suse.cz>
    Cc: <stable@vger.kernel.org>	[4.13+]
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    9b7ea46a
page_isolation.c 9.24 KB