• Vladimir Davydov's avatar
    mm: charge/uncharge kmemcg from generic page allocator paths · 4949148a
    Vladimir Davydov authored
    Currently, to charge a non-slab allocation to kmemcg one has to use
    alloc_kmem_pages helper with __GFP_ACCOUNT flag.  A page allocated with
    this helper should finally be freed using free_kmem_pages, otherwise it
    won't be uncharged.
    
    This API suits its current users fine, but it turns out to be impossible
    to use along with page reference counting, i.e.  when an allocation is
    supposed to be freed with put_page, as it is the case with pipe or unix
    socket buffers.
    
    To overcome this limitation, this patch moves charging/uncharging to
    generic page allocator paths, i.e.  to __alloc_pages_nodemask and
    free_pages_prepare, and zaps alloc/free_kmem_pages helpers.  This way,
    one can use any of the available page allocation functions to get the
    allocated page charged to kmemcg - it's enough to pass __GFP_ACCOUNT,
    just like in case of kmalloc and friends.  A charged page will be
    automatically uncharged on free.
    
    To make it possible, we need to mark pages charged to kmemcg somehow.
    To avoid introducing a new page flag, we make use of page->_mapcount for
    marking such pages.  Since pages charged to kmemcg are not supposed to
    be mapped to userspace, it should work just fine.  There are other
    (ab)users of page->_mapcount - buddy and balloon pages - but we don't
    conflict with them.
    
    In case kmemcg is compiled out or not used at runtime, this patch
    introduces no overhead to generic page allocator paths.  If kmemcg is
    used, it will be plus one gfp flags check on alloc and plus one
    page->_mapcount check on free, which shouldn't hurt performance, because
    the data accessed are hot.
    
    Link: http://lkml.kernel.org/r/a9736d856f895bcb465d9f257b54efe32eda6f99.1464079538.git.vdavydov@virtuozzo.com
    
    Signed-off-by: default avatarVladimir Davydov <vdavydov@virtuozzo.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Michal Hocko <mhocko@kernel.org>
    Cc: Eric Dumazet <eric.dumazet@gmail.com>
    Cc: Minchan Kim <minchan@kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    4949148a