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compactsnoop(8) System Manager's Manual compactsnoop(8)

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

Print usage message.
Include a timestamp column.
Trace this process ID only (filtered in-kernel).
Total duration of trace in seconds.
Output kernel stack trace
Show extended fields.

EXAMPLES

# compactsnoop
# compactsnoop -d 10

FIELDS

Time of the call, in seconds.
Process name
Process ID
Memory node
Zone of the node (such as DMA, DMA32, NORMAL eg)
Shows which order alloc cause memory compaction, -1 means all orders (eg: write to /proc/sys/vm/compact_memory)
SYNC OR ASYNC
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

The min watermark of the zone
The low watermark of the zone
The high watermark of the zone
The nr_free_pages of the zone
compact zone's latency
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

2019-11-1 USER COMMANDS