linux-kernel - Re: [PATCH] mm/compaction: Reduce unnecessary loops

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Date: Sat, 13 Jan 2024 13:52:17 +0800
From: "Bang Li" <libang.li@...group.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc:  <linux-mm@...ck.org>,
   <linux-kernel@...r.kernel.org>,
  "朱辉(茶水)" <teawater@...group.com>,
  "Yan Yan(cailing)" <yanyan.yan@...group.com>
Subject: Re: [PATCH] mm/compaction: Reduce unnecessary loops


On 2024/1/13 3:25, Andrew Morton wrote:
> On Fri, 12 Jan 2024 15:35:24 +0800 "Bang Li" <libang.li@...group.com> wrote:
> 
>> Compaction will be triggered when we write 1 to '/proc/sys/vm/
>> compact_memory'. During the execution of the process, when we send
>> SIGKILL to terminate the compaction, the process does not exit
>> immediately. Instead, it will continue to loop through the remaining
>> zones and nodes before exiting.
>>
>> in my environment:
>>
>> [root]# cat /proc/buddyinfo
>> Node 0, zone      DMA      1      1      1      0      2      1      1      0      1      1      3
>> Node 0, zone    DMA32   1666   1123    804    625    488    356    321    278    209    178    250
>> Node 0, zone   Normal  58852  83160  49983   9812   2287   1229  19604  24471  10346   5219  12205
>> [root]# echo 1 > /sys/kernel/debug/tracing/events/compaction/mm_compaction_end/enable
>>
>> before the patch:
>>
>> [root]# timeout --signal=SIGKILL 0.002 bash -c 'echo 1 > /proc/sys/vm/compact_memory'
>> [root]# cat /sys/kernel/debug/tracing/trace_pipe
>>             <...>-26494   [014] .....   226.468993: mm_compaction_end: zone_start=0x1 migrate_pfn=0xe00 free_pfn=0xe00 zone_end=0x1000, mode=sync status=complete
>>             <...>-26494   [014] .....   226.469718: mm_compaction_end: zone_start=0x1000 migrate_pfn=0x20a80 free_pfn=0xffe00 zone_end=0x100000, mode=sync status=contended
>>             <...>-26494   [014] .....   226.469720: mm_compaction_end: zone_start=0x100000 migrate_pfn=0x100000 free_pfn=0x307fe00 zone_end=0x3080000, mode=sync status=contended
>>
>> after the patch:
>>
>> [root]# timeout --signal=SIGKILL 0.002 bash -c 'echo 1 > /proc/sys/vm/compact_memory'
>> [root]# cat /sys/kernel/debug/tracing/trace_pipe
>>             <...>-17491   [053] .....   109.005387: mm_compaction_end: zone_start=0x1 migrate_pfn=0xe00 free_pfn=0xe00 zone_end=0x1000, mode=sync status=complete
>>             <...>-17491   [053] .....   109.006139: mm_compaction_end: zone_start=0x1000 migrate_pfn=0x22220 free_pfn=0xffe00 zone_end=0x100000, mode=sync status=contended
>>
>> Although it exits quickly after receiving the SIGKILL signal, a better
>> solution is to terminate the loop early after receiving the SIGKILL
>> signal.
>>
> 
> What is the use case here?  The requirement?  Why is this change
> valuable to anyone?

Thanks for the quick reply! I'm very sorry that my inappropriate use
case confused you. What I want to explain is that when receiving the
SIGKILL signal, we can break in advance to reduce unnecessary loops.
This is a clean up patch, the purpose is to reduce the execution of
unnecessary code. If possible, I will remove the confusing use case
in V2.

Thanks,
Bang