Re: [PATCH] mm: compaction: optimize compact_memory to comply with the admin-guide

[Wen Yang]

在 2023/4/13 00:54, Wen Yang 写道:
> 在 2023/4/12 04:48, Andrew Morton 写道:
> > On Wed, 12 Apr 2023 02:24:26 +0800 wenyang.linux@xxxxxxxxxxx wrote:
> >
> > > For the /proc/sys/vm/compact_memory file, the admin-guide states:
> > > When 1 is written to the file, all zones are compacted such that free
> > > memory is available in contiguous blocks where possible. This can be
> > > important for example in the allocation of huge pages although 
> > > processes
> > > will also directly compact memory as required
> > >
> > > But it was not strictly followed, writing any value would cause all
> > > zones to be compacted. In some critical scenarios, some applications
> > > operating it, such as echo 0, have caused serious problems.
> > Really?  You mean someone actually did this and didn't observe the
> > effect during their testing?
>
> Thanks for your reply.
>
> Since /proc/sys/vm/compact_memory has been well documented for over a 
> decade:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/Documentation/admin-guide/sysctl/vm.rst#n109 
>
>
> it is believed that only writing 1 will trigger trigger all zones to 
> be compacted.
>
> Especially for those who write applications, they may only focus on 
> documentation and generally do not read kernel code.  Moreover, such 
> problems are not easily detected through testing on low pressure 
> machines.
>
> Writing any meaningful or meaningless values will trigger it and 
> affect the entire server:
>
> # echo 1 > /proc/sys/vm/compact_memory
> # echo 0 > /proc/sys/vm/compact_memory
> # echo dead > /proc/sys/vm/compact_memory
> # echo "hello world" > /proc/sys/vm/compact_memory
>
> The implementation of this high-risk operation may require following 
> the admin-guides.
>
> --
>
> Best wishes,
>
> Wen
Hello, do you think it's better to optimize the 
sysctl_compaction_handler code or update the admin-guide document?

--

Best wishes,

Wen

> > > It has been slightly optimized to comply with the admin-guide.