NAME

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

SYNOPSIS

       compactsnoop.py [-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