• Minchan Kim's avatar
    mm: don't be stuck to rmap lock on reclaim path · 6d4675e6
    Minchan Kim authored
    The rmap locks(i_mmap_rwsem and anon_vma->root->rwsem) could be contended
    under memory pressure if processes keep working on their vmas(e.g., fork,
    mmap, munmap).  It makes reclaim path stuck.  In our real workload traces,
    we see kswapd is waiting the lock for 300ms+(worst case, a sec) and it
    makes other processes entering direct reclaim, which were also stuck on
    the lock.
    
    This patch makes lru aging path try_lock mode like shink_page_list so the
    reclaim context will keep working with next lru pages without being stuck.
    if it found the rmap lock contended, it rotates the page back to head of
    lru in both active/inactive lrus to make them consistent behavior, which
    is basic starting point rather than adding more heristic.
    
    Since this patch introduces a new "contended" field as out-param along
    with try_lock in-param in rmap_walk_control, it's not immutable any longer
    if the try_lock is set so remove const keywords on rmap related functions.
    Since rmap walking is already expensive operation, I doubt the const
    would help sizable benefit( And we didn't have it until 5.17).
    
    In a heavy app workload in Android, trace shows following statistics.  It
    almost removes rmap lock contention from reclaim path.
    
    Martin Liu reported:
    
    Before:
    
       max_dur(ms)  min_dur(ms)  max-min(dur)ms  avg_dur(ms)  sum_dur(ms)  count blocked_function
             1632            0            1631   151.542173        31672    209  page_lock_anon_vma_read
              601            0             601   145.544681        28817    198  rmap_walk_file
    
    After:
    
       max_dur(ms)  min_dur(ms)  max-min(dur)ms  avg_dur(ms)  sum_dur(ms)  count blocked_function
              NaN          NaN              NaN          NaN          NaN    0.0             NaN
                0            0                0     0.127645            1     12  rmap_walk_file
    
    [minchan@kernel.org: add comment, per Matthew]
      Link: https://lkml.kernel.org/r/YnNqeB5tUf6LZ57b@google.com
    Link: https://lkml.kernel.org/r/20220510215423.164547-1-minchan@kernel.orgSigned-off-by: default avatarMinchan Kim <minchan@kernel.org>
    Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
    Cc: Suren Baghdasaryan <surenb@google.com>
    Cc: Michal Hocko <mhocko@suse.com>
    Cc: John Dias <joaodias@google.com>
    Cc: Tim Murray <timmurray@google.com>
    Cc: Matthew Wilcox <willy@infradead.org>
    Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
    Cc: Martin Liu <liumartin@google.com>
    Cc: Minchan Kim <minchan@kernel.org>
    Cc: Matthew Wilcox <willy@infradead.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    6d4675e6
memory-failure.c 63 KB