From: Marcelo Tosatti <mtosatti@redhat•com>
To: Peter Zijlstra <peterz@infradead•org>
Cc: geert+renesas@glider•be, tony@atomide•com,
linus.walleij@linaro•org, dave.hansen@linux•intel.com,
Yair Podemsky <ypodemsk@redhat•com>,
sebastian.reichel@collabora•com, linux-mm@kvack•org,
hpa@zytor•com, sparclinux@vger•kernel.org,
agordeev@linux•ibm.com, will@kernel•org, ardb@kernel•org,
linux-arch@vger•kernel.org, linux-s390@vger•kernel.org,
vschneid@redhat•com, arnd@arndb•de, paulmck@kernel•org,
aneesh.kumar@linux•ibm.com, x86@kernel•org,
linux@armlinux•org.uk, mingo@redhat•com, samitolvanen@google•com,
borntraeger@linux•ibm.com, hca@linux•ibm.com,
keescook@chromium•org, gor@linux•ibm.com,
Frederic Weisbecker <frederic@kernel•org>,
npiggin@gmail•com, rmk+kernel@armlinux•org.uk, bp@alien8•de,
nick.hawkins@hpe•com, tglx@linutronix•de, jpoimboe@kernel•org,
linux-arm-kernel@lists•infradead.org, alougovs@redhat•com,
linux-kernel@vger•kernel.org, juerg.haefliger@canonical•com,
svens@linux•ibm.com, dhildenb@redhat•com,
akpm@linux-foundation•org, linuxppc-dev@lists•ozlabs.org,
davem@da vemloft.net
Subject: Re: [PATCH 3/3] mm/mmu_gather: send tlb_remove_table_smp_sync IPI only to CPUs in kernel mode
Date: Thu, 6 Apr 2023 09:38:50 -0300 [thread overview]
Message-ID: <ZC69Wmqjdwk+I8kn@tpad> (raw)
In-Reply-To: <20230405195226.GB365912@hirez.programming.kicks-ass.net>
On Wed, Apr 05, 2023 at 09:52:26PM +0200, Peter Zijlstra wrote:
> On Wed, Apr 05, 2023 at 04:45:32PM -0300, Marcelo Tosatti wrote:
> > On Wed, Apr 05, 2023 at 01:10:07PM +0200, Frederic Weisbecker wrote:
> > > On Wed, Apr 05, 2023 at 12:44:04PM +0200, Frederic Weisbecker wrote:
> > > > On Tue, Apr 04, 2023 at 04:42:24PM +0300, Yair Podemsky wrote:
> > > > > + int state = atomic_read(&ct->state);
> > > > > + /* will return true only for cpus in kernel space */
> > > > > + return state & CT_STATE_MASK == CONTEXT_KERNEL;
> > > > > +}
> > > >
> > > > Also note that this doesn't stricly prevent userspace from being interrupted.
> > > > You may well observe the CPU in kernel but it may receive the IPI later after
> > > > switching to userspace.
> > > >
> > > > We could arrange for avoiding that with marking ct->state with a pending work bit
> > > > to flush upon user entry/exit but that's a bit more overhead so I first need to
> > > > know about your expectations here, ie: can you tolerate such an occasional
> > > > interruption or not?
> > >
> > > Bah, actually what can we do to prevent from that racy IPI? Not much I fear...
> >
> > Use a different mechanism other than an IPI to ensure in progress
> > __get_free_pages_fast() has finished execution.
> >
> > Isnt this codepath slow path enough that it can use
> > synchronize_rcu_expedited?
>
> To actually hit this path you're doing something really dodgy.
Apparently khugepaged is using the same infrastructure:
$ grep tlb_remove_table khugepaged.c
tlb_remove_table_sync_one();
tlb_remove_table_sync_one();
So just enabling khugepaged will hit that path.
next prev parent reply other threads:[~2023-04-06 13:18 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-04 13:42 [PATCH 0/3] send tlb_remove_table_smp_sync IPI only to necessary CPUs Yair Podemsky
2023-04-04 13:42 ` [PATCH 1/3] arch: Introduce ARCH_HAS_CPUMASK_BITS Yair Podemsky
2023-04-04 13:47 ` David Hildenbrand
2023-04-04 13:42 ` [PATCH 2/3] mm/mmu_gather: send tlb_remove_table_smp_sync IPI only to MM CPUs Yair Podemsky
2023-04-04 14:57 ` Peter Zijlstra
2023-04-04 13:42 ` [PATCH 3/3] mm/mmu_gather: send tlb_remove_table_smp_sync IPI only to CPUs in kernel mode Yair Podemsky
2023-04-04 14:03 ` David Hildenbrand
2023-04-04 15:12 ` Peter Zijlstra
2023-04-04 16:00 ` Peter Zijlstra
2023-04-05 10:43 ` Frederic Weisbecker
2023-04-05 11:10 ` Frederic Weisbecker
2023-04-05 11:41 ` Peter Zijlstra
2023-04-05 12:00 ` David Hildenbrand
2023-04-05 12:05 ` Frederic Weisbecker
2023-04-05 12:31 ` Frederic Weisbecker
2023-04-05 12:45 ` Valentin Schneider
2023-04-06 13:38 ` Peter Zijlstra
2023-04-06 14:11 ` Valentin Schneider
2023-04-06 14:39 ` Peter Zijlstra
2023-04-05 19:45 ` Marcelo Tosatti
2023-04-05 19:52 ` Peter Zijlstra
2023-04-06 12:38 ` Marcelo Tosatti [this message]
2023-04-06 13:29 ` Peter Zijlstra
2023-04-06 14:04 ` Peter Zijlstra
2023-04-06 14:42 ` David Hildenbrand
2023-04-06 15:06 ` Peter Zijlstra
2023-04-06 15:02 ` Peter Zijlstra
2023-04-06 15:51 ` David Hildenbrand
2023-04-06 18:27 ` Peter Zijlstra
2023-04-19 11:30 ` David Hildenbrand
2023-04-19 11:39 ` Marcelo Tosatti
2023-04-05 19:43 ` Marcelo Tosatti
2023-04-05 19:54 ` Peter Zijlstra
2023-04-06 12:49 ` Marcelo Tosatti
2023-04-06 13:32 ` Peter Zijlstra
2023-04-19 11:01 ` Marcelo Tosatti
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