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Date: Fri, 12 Jan 2024 11:25:51 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: "Bang Li" <libang.li@antgroup.com>
Cc: <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>, =?UTF-8?Q?"?=
 =?UTF-8?Q?=E6=9C=B1=E8=BE=89(=E8=8C=B6=E6=B0=B4)"?=
 <teawater@antgroup.com>, "Yan Yan(cailing)" <yanyan.yan@antgroup.com>
Subject: Re: [PATCH] mm/compaction: Reduce unnecessary loops
Message-Id: <20240112112551.bbc9d5114fd2c6fb421fed2d@linux-foundation.org>
In-Reply-To: <20240112073524.80724-1-libang.li@antgroup.com>
References: <20240112073524.80724-1-libang.li@antgroup.com>
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On Fri, 12 Jan 2024 15:35:24 +0800 "Bang Li" <libang.li@antgroup.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?