---
name: "compactsnoop-bpfcc"
section: "8"
platform: "linux"
package: "bpfcc-tools"
version: "0.31.0+ds-7"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/compactsnoop-bpfcc"
---

# compactsnoop-bpfcc(8)

Trace compact zone events. Uses Linux eBPF/bcc.

## 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