• Mel Gorman's avatar
    mm: compaction: Abort async compaction if locks are contended or taking too long · c67fe375
    Mel Gorman authored
    Jim Schutt reported a problem that pointed at compaction contending
    heavily on locks.  The workload is straight-forward and in his own words;
    
    	The systems in question have 24 SAS drives spread across 3 HBAs,
    	running 24 Ceph OSD instances, one per drive.  FWIW these servers
    	are dual-socket Intel 5675 Xeons w/48 GB memory.  I've got ~160
    	Ceph Linux clients doing dd simultaneously to a Ceph file system
    	backed by 12 of these servers.
    
    Early in the test everything looks fine
    
      procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu-------
       r  b       swpd       free       buff      cache   si   so    bi    bo   in   cs  us sy  id wa st
      31 15          0     287216        576   38606628    0    0     2  1158    2   14   1  3  95  0  0
      27 15          0     225288        576   38583384    0    0    18 2222016 203357 134876  11 56  17 15  0
      28 17          0     219256        576   38544736    0    0    11 2305932 203141 146296  11 49  23 17  0
       6 18          0     215596        576   38552872    0    0     7 2363207 215264 166502  12 45  22 20  0
      22 18          0     226984        576   38596404    0    0     3 2445741 223114 179527  12 43  23 22  0
    
    and then it goes to pot
    
      procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu-------
       r  b       swpd       free       buff      cache   si   so    bi    bo   in   cs  us sy  id wa st
      163  8          0     464308        576   36791368    0    0    11 22210  866  536   3 13  79  4  0
      207 14          0     917752        576   36181928    0    0   712 1345376 134598 47367   7 90   1  2  0
      123 12          0     685516        576   36296148    0    0   429 1386615 158494 60077   8 84   5  3  0
      123 12          0     598572        576   36333728    0    0  1107 1233281 147542 62351   7 84   5  4  0
      622  7          0     660768        576   36118264    0    0   557 1345548 151394 59353   7 85   4  3  0
      223 11          0     283960        576   36463868    0    0    46 1107160 121846 33006   6 93   1  1  0
    
    Note that system CPU usage is very high blocks being written out has
    dropped by 42%. He analysed this with perf and found
    
      perf record -g -a sleep 10
      perf report --sort symbol --call-graph fractal,5
        34.63%  [k] _raw_spin_lock_irqsave
                |
                |--97.30%-- isolate_freepages
                |          compaction_alloc
                |          unmap_and_move
                |          migrate_pages
                |          compact_zone
                |          compact_zone_order
                |          try_to_compact_pages
                |          __alloc_pages_direct_compact
                |          __alloc_pages_slowpath
                |          __alloc_pages_nodemask
                |          alloc_pages_vma
                |          do_huge_pmd_anonymous_page
                |          handle_mm_fault
                |          do_page_fault
                |          page_fault
                |          |
                |          |--87.39%-- skb_copy_datagram_iovec
                |          |          tcp_recvmsg
                |          |          inet_recvmsg
                |          |          sock_recvmsg
                |          |          sys_recvfrom
                |          |          system_call
                |          |          __recv
                |          |          |
                |          |           --100.00%-- (nil)
                |          |
                |           --12.61%-- memcpy
                 --2.70%-- [...]
    
    There was other data but primarily it is all showing that compaction is
    contended heavily on the zone->lock and zone->lru_lock.
    
    commit [b2eef8c0: mm: compaction: minimise the time IRQs are disabled
    while isolating pages for migration] noted that it was possible for
    migration to hold the lru_lock for an excessive amount of time. Very
    broadly speaking this patch expands the concept.
    
    This patch introduces compact_checklock_irqsave() to check if a lock
    is contended or the process needs to be scheduled. If either condition
    is true then async compaction is aborted and the caller is informed.
    The page allocator will fail a THP allocation if compaction failed due
    to contention. This patch also introduces compact_trylock_irqsave()
    which will acquire the lock only if it is not contended and the process
    does not need to schedule.
    Reported-by: default avatarJim Schutt <jaschut@sandia.gov>
    Tested-by: default avatarJim Schutt <jaschut@sandia.gov>
    Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    c67fe375
compaction.h 3.17 KB