linux-kernel - Re: [RFC v2 PATCH 4/5] vmstat: add page-cache numa hints

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Message-ID: <Z27MkaURRciLbq64@gourry-fedora-PF4VCD3F>
Date: Fri, 27 Dec 2024 10:49:37 -0500
From: Gregory Price <gourry@...rry.net>
To: Donet Tom <donettom@...ux.ibm.com>
Cc: Gregory Price <gourry@...rry.net>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, nehagholkar@...a.com,
	abhishekd@...a.com, kernel-team@...a.com, david@...hat.com,
	nphamcs@...il.com, akpm@...ux-foundation.org, hannes@...xchg.org,
	kbusch@...a.com, ying.huang@...ux.alibaba.com
Subject: Re: [RFC v2 PATCH 4/5] vmstat: add page-cache numa hints

On Fri, Dec 27, 2024 at 04:18:24PM +0530, Donet Tom wrote:
> 
> On 12/11/24 03:07, Gregory Price wrote:
... snip ...
> > +		NUMA_HINT_PAGE_CACHE,
> > +		NUMA_HINT_PAGE_CACHE_LOCAL,
> >   		NUMA_PAGE_MIGRATE,
... snip ...
> >   	if (folio_nid(folio) == numa_node_id()) {
> > -		count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
> > +		count_vm_numa_event(NUMA_HINT_TYPE_LOCAL(vmf));
> 
> I have tested this patch series on my system with my test program. I am able
> to see unmapped page cache pages are getting promoted.
> numa_hint_faults2269numa_hint_faults_local2245numa_hint_page_cache1244numa_hint_page_cache_local0numa_pages_migrated4501
> 
> In my test result numa_hint_page_cache_local is 0. I am seeing
> numa_hint_page_cache_local will only be incremented if the folio's
> node and the process's running node are the same. This condition
> does not occur in the current implementation, correct?
> 

I did not want to assume we'd never use this interface where such a
scenario could occur - so i wanted to:

  a) make such a scenario visible
  b) make the code consistent with existing fault counts

I'm fine removing it.  It's hard to know if this interface ever gets
called with that scenario occurringwithout capturing the data.

~Gregory