linux-kernel - Re: [PATCH v2 1/4] mm/page_alloc/vmstat: Simplify refresh_cpu_vm

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Message-Id: <20250926183343.54956-1-sj@kernel.org>
Date: Fri, 26 Sep 2025 11:33:43 -0700
From: SeongJae Park <sj@...nel.org>
To: Joshua Hahn <joshua.hahnjy@...il.com>
Cc: SeongJae Park <sj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Chris Mason <clm@...com>,
	Kiryl Shutsemau <kirill@...temov.name>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Brendan Jackman <jackmanb@...gle.com>,
	David Hildenbrand <david@...hat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Michal Hocko <mhocko@...e.com>,
	Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Zi Yan <ziy@...dia.com>,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	kernel-team@...a.com
Subject: Re: [PATCH v2 1/4] mm/page_alloc/vmstat: Simplify refresh_cpu_vm_stats change detection

On Fri, 26 Sep 2025 11:24:37 -0700 Joshua Hahn <joshua.hahnjy@...il.com> wrote:
[...]
> > > @@ -839,7 +839,7 @@ static int refresh_cpu_vm_stats(bool do_pagesets)
> > >  		if (do_pagesets) {
> > >  			cond_resched();
> > >  
> > > -			changes += decay_pcp_high(zone, this_cpu_ptr(pcp));
> > > +			changed |= decay_pcp_high(zone, this_cpu_ptr(pcp));
> > 
> > I'm not a fan of bit operations unless it provides clear benefits.
> > What about below?
> > 
> >     if (decay_pcp_high(zone, this_cpu_ptr(pcp)) && !changed)
> >     	changed = truee;
> 
> Here, what if I change it to just:
> 
> 	if (decay_pcp_high(zone, this_cpu_ptr(pcp))
> 		changed = true;

Looks nice to me! :)

> 
> Since even if changed == true already, this will be a no-op.

I was thinking the compiler might or might not emit unnecessary writes, but I
don't really care that.  Your suggested version looks good to me :)

> 
> > Just a personal and trivial taste.  No strong opinion.  If you don't strongly
> > feel my suggestion is better, please keep the original code.
> 
> I feel like if someone (you) feels like bitwise operations here makes it
> less clear what the code is doing, others may feel the same way as well!
> Happy to make the change to hopefully make it more easily understandable
> what is happening. 

Thank you Joshua!

[...]
> Thanks SJ, I hope you have a great day!

You too!  Plus, great weekend!


Thanks,
SJ

[...]