linux-kernel - Re: [RFC PATCH 0/4] Add hazard pointers to kernel

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Message-ID: <CAHk-=wgLrENN2JFZf8j9TDXcfmnZ8BNU_u=6QrEOti-s6aMrbg@mail.gmail.com>
Date: Thu, 19 Sep 2024 16:21:36 +0200
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Christoph Hellwig <hch@...radead.org>
Cc: Boqun Feng <boqun.feng@...il.com>, linux-kernel@...r.kernel.org, rcu@...r.kernel.org, 
	linux-mm@...ck.org, lkmm@...r.kernel.org, 
	"Paul E. McKenney" <paulmck@...nel.org>, Frederic Weisbecker <frederic@...nel.org>, 
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>, Joel Fernandes <joel@...lfernandes.org>, 
	Josh Triplett <josh@...htriplett.org>, Uladzislau Rezki <urezki@...il.com>, 
	Steven Rostedt <rostedt@...dmis.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
	Lai Jiangshan <jiangshanlai@...il.com>, Zqiang <qiang.zhang1211@...il.com>, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>, 
	Waiman Long <longman@...hat.com>, Mark Rutland <mark.rutland@....com>, 
	Thomas Gleixner <tglx@...utronix.de>, Kent Overstreet <kent.overstreet@...il.com>, 
	Vlastimil Babka <vbabka@...e.cz>, maged.michael@...il.com
Subject: Re: [RFC PATCH 0/4] Add hazard pointers to kernel

On Thu, 19 Sept 2024 at 16:15, Christoph Hellwig <hch@...radead.org> wrote:
>
> Agreed.  From the description this would seem like a good fit for
> q_usage_counter in the block layer, which currently makes creative use
> of percpu counters.

Yes, if this actually could simplify code that currently used percpu
counters, that might be lovely.

The percpu counters often perform very well, but then have huge pain
in either managing the percpu allocation, or in trying to synchronize
across CPU's.

I'd be a lot more interested in "we can fix complex code" than in "we
have crappy code in bad subsystems where we can hide the performance
impact of the subsystem not having been done right".

               Linus