| 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¶
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.
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 |