Re: [PATCH] mm/compaction: Reduce unnecessary loops

[Bang Li]

On 2024/1/13 3:25, Andrew Morton wrote:
> On Fri, 12 Jan 2024 15:35:24 +0800 "Bang Li" <libang.li@xxxxxxxxxxxx> 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