• KAMEZAWA Hiroyuki's avatar
    bugfix for memory cgroup controller: migration under memory controller fix · ae41be37
    KAMEZAWA Hiroyuki authored
    While using memory control cgroup, page-migration under it works as following.
    ==
     1. uncharge all refs at try to unmap.
     2. charge regs again remove_migration_ptes()
    ==
    This is simple but has following problems.
    ==
     The page is uncharged and charged back again if *mapped*.
        - This means that cgroup before migration can be different from one after
          migration
        - If page is not mapped but charged as page cache, charge is just ignored
          (because not mapped, it will not be uncharged before migration)
          This is memory leak.
    ==
    This patch tries to keep memory cgroup at page migration by increasing
    one refcnt during it. 3 functions are added.
    
     mem_cgroup_prepare_migration() --- increase refcnt of page->page_cgroup
     mem_cgroup_end_migration()     --- decrease refcnt of page->page_cgroup
     mem_cgroup_page_migration() --- copy page->page_cgroup from old page to
                                     new page.
    
    During migration
      - old page is under PG_locked.
      - new page is under PG_locked, too.
      - both old page and new page is not on LRU.
    
    These 3 facts guarantee that page_cgroup() migration has no race.
    
    Tested and worked well in x86_64/fake-NUMA box.
    Signed-off-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
    Cc: Pavel Emelianov <xemul@openvz.org>
    Cc: Paul Menage <menage@google.com>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: "Eric W. Biederman" <ebiederm@xmission.com>
    Cc: Nick Piggin <nickpiggin@yahoo.com.au>
    Cc: Kirill Korotaev <dev@sw.ru>
    Cc: Herbert Poetzl <herbert@13thfloor.at>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    ae41be37
migrate.c 23.7 KB