• Michal Hocko's avatar
    oom, trace: add oom detection tracepoints · d379f01d
    Michal Hocko authored
    should_reclaim_retry is the central decision point for declaring the
    OOM.  It might be really useful to expose data used for this decision
    making when debugging an unexpected oom situations.
    
    Say we have an OOM report:
    [   52.264001] mem_eater invoked oom-killer: gfp_mask=0x24280ca(GFP_HIGHUSER_MOVABLE|__GFP_ZERO), nodemask=0, order=0, oom_score_adj=0
    [   52.267549] CPU: 3 PID: 3148 Comm: mem_eater Tainted: G        W       4.8.0-oomtrace3-00006-gb21338b386d2 #1024
    
    Now we can check the tracepoint data to see how we have ended up in this
    situation:
           mem_eater-3148  [003] ....    52.432801: reclaim_retry_zone: node=0 zone=DMA32 order=0 reclaimable=51 available=11134 min_wmark=11084 no_progress_loops=1 wmark_check=1
           mem_eater-3148  [003] ....    52.433269: reclaim_retry_zone: node=0 zone=DMA32 order=0 reclaimable=51 available=11103 min_wmark=11084 no_progress_loops=1 wmark_check=1
           mem_eater-3148  [003] ....    52.433712: reclaim_retry_zone: node=0 zone=DMA32 order=0 reclaimable=51 available=11100 min_wmark=11084 no_progress_loops=2 wmark_check=1
           mem_eater-3148  [003] ....    52.434067: reclaim_retry_zone: node=0 zone=DMA32 order=0 reclaimable=51 available=11097 min_wmark=11084 no_progress_loops=3 wmark_check=1
           mem_eater-3148  [003] ....    52.434414: reclaim_retry_zone: node=0 zone=DMA32 order=0 reclaimable=51 available=11094 min_wmark=11084 no_progress_loops=4 wmark_check=1
           mem_eater-3148  [003] ....    52.434761: reclaim_retry_zone: node=0 zone=DMA32 order=0 reclaimable=51 available=11091 min_wmark=11084 no_progress_loops=5 wmark_check=1
           mem_eater-3148  [003] ....    52.435108: reclaim_retry_zone: node=0 zone=DMA32 order=0 reclaimable=51 available=11087 min_wmark=11084 no_progress_loops=6 wmark_check=1
           mem_eater-3148  [003] ....    52.435478: reclaim_retry_zone: node=0 zone=DMA32 order=0 reclaimable=51 available=11084 min_wmark=11084 no_progress_loops=7 wmark_check=0
           mem_eater-3148  [003] ....    52.435478: reclaim_retry_zone: node=0 zone=DMA order=0 reclaimable=0 available=1126 min_wmark=179 no_progress_loops=7 wmark_check=0
    
    The above shows that we can quickly deduce that the reclaim stopped
    making any progress (see no_progress_loops increased in each round) and
    while there were still some 51 reclaimable pages they couldn't be
    dropped for some reason (vmscan trace points would tell us more about
    that part).  available will represent reclaimable + free_pages scaled
    down per no_progress_loops factor.  This is essentially an optimistic
    estimate of how much memory we would have when reclaiming everything.
    This can be compared to min_wmark to get a rought idea but the
    wmark_check tells the result of the watermark check which is more
    precise (includes lowmem reserves, considers the order etc.).  As we can
    see no zone is eligible in the end and that is why we have triggered the
    oom in this situation.
    
    Please note that higher order requests might fail on the wmark_check
    even when there is much more memory available than min_wmark - e.g.
    when the memory is fragmented.  A follow up tracepoint will help to
    debug those situations.
    
    Link: http://lkml.kernel.org/r/20161220130135.15719-3-mhocko@kernel.orgSigned-off-by: default avatarMichal Hocko <mhocko@suse.com>
    Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    d379f01d
oom.h 1.94 KB