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

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Message-Id: <20240112112551.bbc9d5114fd2c6fb421fed2d@linux-foundation.org>
Date: Fri, 12 Jan 2024 11:25:51 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: "Bang Li" <libang.li@...group.com>
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 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?