linux-kernel - Re: [PATCH v3] alloc_tag: add per-NUMA node stats

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Message-ID: <CALCePG1h8NE010EGpBh8CxhiWqr4-GantEJ4P0Dnck+cnioBiw@mail.gmail.com>
Date: Thu, 10 Jul 2025 18:07:13 -0700
From: Casey Chen <cachen@...estorage.com>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: akpm@...ux-foundation.org, surenb@...gle.com, corbet@....net, 
	dennis@...nel.org, tj@...nel.org, cl@...two.org, vbabka@...e.cz, 
	mhocko@...e.com, jackmanb@...gle.com, hannes@...xchg.org, ziy@...dia.com, 
	rientjes@...gle.com, roman.gushchin@...ux.dev, harry.yoo@...cle.com, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org, 
	yzhong@...estorage.com, souravpanda@...gle.com, 00107082@....com
Subject: Re: [PATCH v3] alloc_tag: add per-NUMA node stats

On Thu, Jul 10, 2025 at 5:54 PM Kent Overstreet
<kent.overstreet@...ux.dev> wrote:
>
> On Thu, Jul 10, 2025 at 05:42:05PM -0700, Casey Chen wrote:
> > Hi All,
> >
> > Thanks for reviewing my previous patches. I am replying some comments
> > in our previous discussion
> > https://lore.kernel.org/all/CAJuCfpHhSUhxer-6MP3503w6520YLfgBTGp7Q9Qm9kgN4TNsfw@mail.gmail.com/T/#u
> >
> > Most people care about the motivations and usages of this feature.
> > Internally, we used to have systems having asymmetric memory to NUMA
> > nodes. Node 0 uses a lot of memory but node 1 is pretty empty.
> > Requests to allocate memory on node 0 always fail. With this patch, we
> > can find the imbalance and optimize the memory usage. Also, David
> > Rientjes and Sourav Panda provide their scenarios in which this patch
> > would be very useful. It is easy to turn on an off so I think it is
> > nice to have, enabling more scenarios in the future.
> >
> > Andrew / Kent,
> > * I agree with Kent on using for_each_possible_cpu rather than
> > for_each_online_cpu, considering CPU online/offline.
> > * When failing to allocate counters for in-kernel alloc_tag, panic()
> > is better than WARN(), eventually the kernel would panic at invalid
> > memory access.
> > * percpu stats would bloat data structures quite a bit.
> >
> > David Wang,
> > I don't really understand what is 'granularity of calling sites'. If
> > NUMA imbalance is found, the calling site could request memory
> > allocation from different nodes. Other factors can affect NUMA
> > balance, those information can be implemented in a different patch.
>
> Let's get this functionality in.
>
> We've already got userspace parsing and consuming /proc/allocinfo, so we
> just need to do it without changing that format.

You mean keep the format without per-NUMA info the same as before ?
My patch v3 changed the header and the alignment of bytes and calls. I
can restore them back.

-       seq_buf_printf(buf, "#     <size>  <calls> <tag info>\n");
+       seq_buf_printf(buf, "<size> <calls> <tag info>\n");

-       seq_buf_printf(out, "%12lli %8llu ", bytes, counter.calls);
+       seq_buf_printf(out, "%-12lli %-8llu ", bytes, counter.calls);