NAME

       compactsnoop - Trace compact zone events. Uses Linux eBPF/bcc.

SYNOPSIS

       compactsnoop [-h] [-T] [-p PID] [-d DURATION] [-K] [-e]

DESCRIPTION

       compactsnoop  traces  the  compact  zone  events,  showing which processes are allocing pages with memory
       compaction. This can be useful for discovering when compact_stall (/proc/vmstat) continues  to  increase,
       whether it is caused by some critical processes or not.

       This works by tracing the compact zone events using raw_tracepoints and one kretprobe.

       For  the  Centos  7.6  (3.10.x  kernel),  see  the  version  under  tools/old, which uses an older memory
       compaction mechanism.

       Since this uses BPF, only the root user can use this tool.

REQUIREMENTS

       CONFIG_BPF and bcc.

OPTIONS

       -h     Print usage message.

       -T     Include a timestamp column.

       -p PID Trace this process ID only (filtered in-kernel).

       -d DURATION
              Total duration of trace in seconds.

       -K     Output kernel stack trace

       -e     Show extended fields.

EXAMPLES

       Trace all compact zone events:
              # compactsnoop

       Trace all compact zone events, for 10 seconds only:
              # compactsnoop -d 10

FIELDS

       TIME(s)
              Time of the call, in seconds.

       COMM   Process name

       PID    Process ID

       NODE   Memory node

       ZONE   Zone of the node (such as DMA, DMA32, NORMAL eg)

       ORDER  Shows  which  order  alloc  cause  memory  compaction,  -1  means  all  orders   (eg:   write   to
              /proc/sys/vm/compact_memory)

       MODE   SYNC OR ASYNC

       FRAGIDX (extra column)
              The  FRAGIDX  is  short  for  fragmentation  index,  which  only makes sense if an allocation of a
              requested size would fail. If that is true, the fragmentation  index  indicates  whether  external
              fragmentation  or  a  lack  of  memory was the problem. The value can be used to determine if page
              reclaim or compaction should be used.

               Index is between 0 and 1 so return within 3 decimal places

               0 => allocation would fail due to lack of memory

               1 => allocation would fail due to fragmentation

       MIN (extra column)
              The min watermark of the zone

       LOW (extra column)
              The low watermark of the zone

       HIGH (extra column)
              The high watermark of the zone

       FREE (extra column)
              The nr_free_pages of the zone

       LAT(ms)
              compact zone's latency

       STATUS The compaction's result.

               For (CentOS 7.6's kernel), the status include:

               "skipped" (COMPACT_SKIPPED): compaction didn't start as it was not possible or direct reclaim was
               more suitable

               "continue" (COMPACT_CONTINUE): compaction should continue to another pageblock

               "partial" (COMPACT_PARTIAL): direct compaction partially compacted a zone and there are  suitable
               pages

               "complete" (COMPACT_COMPLETE): The full zone was compacted

               For (kernel 4.7 and above):

               "not_suitable_zone"  (COMPACT_NOT_SUITABLE_ZONE):  For more detailed tracepoint output - internal
               to compaction

               "skipped" (COMPACT_SKIPPED): compaction didn't start as it was not possible or direct reclaim was
               more suitable

               "deferred" (COMPACT_DEFERRED): compaction didn't start as it was deferred due to past failures

               "no_suitable_page" (COMPACT_NOT_SUITABLE_PAGE): For more detailed tracepoint output - internal to
               compaction

               "continue" (COMPACT_CONTINUE): compaction should continue to another pageblock

               "complete" (COMPACT_COMPLETE): The full zone was  compacted  scanned  but  wasn't  successful  to
               compact suitable pages.

               "partial_skipped"  (COMPACT_PARTIAL_SKIPPED):  direct compaction has scanned part of the zone but
               wasn't successful to compact suitable pages.

               "contended" (COMPACT_CONTENDED): compaction terminated prematurely due to lock contentions

               "success" (COMPACT_SUCCESS): direct compaction terminated after concluding  that  the  allocation
               should now succeed

OVERHEAD

       This traces the kernel compact zone kprobe/kretprobe or raw_tracepoints and prints output for each event.
       As  the  rate  of  this  is  generally expected to be low (< 1000/s), the overhead is also expected to be
       negligible.

SOURCE

       This is from bcc.

              https://github.com/iovisor/bcc

       Also look in the bcc distribution for a companion _examples.txt file containing  example  usage,  output,
       and commentary for this tool.

OS

       Linux

STABILITY

       Unstable - in development.

AUTHOR

       Wenbo Zhang

USER COMMANDS                                       2019-11-1                                    compactsnoop(8)