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Date:   Wed, 18 Oct 2023 16:25:56 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     Ankur Arora <ankur.a.arora@oracle.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org,
        akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de,
        dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com,
        juri.lelli@redhat.com, vincent.guittot@linaro.org,
        willy@infradead.org, mgorman@suse.de, rostedt@goodmis.org,
        jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com,
        boris.ostrovsky@oracle.com, konrad.wilk@oracle.com,
        jgross@suse.com, andrew.cooper3@citrix.com,
        Frederic Weisbecker <fweisbec@gmail.com>, urezki@gmail.com
Subject: Re: [PATCH v2 7/9] sched: define TIF_ALLOW_RESCHED
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On Thu, Oct 19, 2023 at 12:53:05AM +0200, Thomas Gleixner wrote:
> On Wed, Oct 18 2023 at 10:51, Paul E. McKenney wrote:
> > On Wed, Oct 18, 2023 at 05:09:46AM -0700, Ankur Arora wrote:
> 
> Can you folks please trim your replies. It's annoying to scroll
> through hundreds of quoted lines to figure out that nothing is there.
> 
> >>  This probably allows for more configuration flexibility across archs?
> >>  Would allow for TREE_RCU=y, for instance. That said, so far I've only
> >>  been working with PREEMPT_RCU=y.)
> >
> > Then this is a bug that needs to be fixed.  We need a way to make
> > RCU readers non-preemptible.
> 
> Why?

So that we don't get tail latencies from preempted RCU readers that
result in memory-usage spikes on systems that have good and sufficient
quantities of memory, but which do not have enough memory to tolerate
readers being preempted.

							Thanx, Paul