• Johannes Weiner's avatar
    mm: memcontrol: convert page cache to a new mem_cgroup_charge() API · 3fea5a49
    Johannes Weiner authored
    The try/commit/cancel protocol that memcg uses dates back to when pages
    used to be uncharged upon removal from the page cache, and thus couldn't
    be committed before the insertion had succeeded.  Nowadays, pages are
    uncharged when they are physically freed; it doesn't matter whether the
    insertion was successful or not.  For the page cache, the transaction
    dance has become unnecessary.
    
    Introduce a mem_cgroup_charge() function that simply charges a newly
    allocated page to a cgroup and sets up page->mem_cgroup in one single
    step.  If the insertion fails, the caller doesn't have to do anything but
    free/put the page.
    
    Then switch the page cache over to this new API.
    
    Subsequent patches will also convert anon pages, but it needs a bit more
    prep work.  Right now, memcg depends on page->mapping being already set up
    at the time of charging, so that it can maintain its own MEMCG_CACHE and
    MEMCG_RSS counters.  For anon, page->mapping is set under the same pte
    lock under which the page is publishd, so a single charge point that can
    block doesn't work there just yet.
    
    The following prep patches will replace the private memcg counters with
    the generic vmstat counters, thus removing the page->mapping dependency,
    then complete the transition to the new single-point charge API and delete
    the old transactional scheme.
    
    v2: leave shmem swapcache when charging fails to avoid double IO (Joonsoo)
    v3: rebase on preceeding shmem simplification patch
    Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Reviewed-by: default avatarAlex Shi <alex.shi@linux.alibaba.com>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
    Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
    Cc: Michal Hocko <mhocko@suse.com>
    Cc: Roman Gushchin <guro@fb.com>
    Cc: Shakeel Butt <shakeelb@google.com>
    Cc: Balbir Singh <bsingharora@gmail.com>
    Link: http://lkml.kernel.org/r/20200508183105.225460-6-hannes@cmpxchg.orgSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    3fea5a49
memcontrol.c 191 KB