From: Rik van Riel <riel@surriel.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
Mike Galbraith <efault@gmx.de>, kernel-team <kernel-team@fb.com>,
Ingo Molnar <mingo@kernel.org>,
Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCH 2/7] x86,tlb: leave lazy TLB mode at page table free time
Date: Thu, 16 Aug 2018 01:31:55 -0400 [thread overview]
Message-ID: <1534397515.28585.138.camel@surriel.com> (raw)
In-Reply-To: <CALCETrWhb4CU8BfjdYBe+QJ8CVa4pzAr3ME+HBe4=6y=Pi9pFQ@mail.gmail.com>
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On Wed, 2018-08-15 at 18:54 -0700, Andy Lutomirski wrote:
> On Mon, Jul 16, 2018 at 12:03 PM, Rik van Riel <riel@surriel.com>
> wrote:
> Hi Rik-
>
> I was looking through this, and I see:
>
> > -static void tlb_remove_table_one(void *table)
> > +static void tlb_remove_table_one(void *table, struct mmu_gather
> > *tlb)
> > {
> > /*
> > * This isn't an RCU grace period and hence the page-tables
> > cannot be
> > @@ -344,7 +348,7 @@ static void tlb_remove_table_one(void *table)
> > * It is however sufficient for software page-table walkers
> > that rely on
> > * IRQ disabling. See the comment near struct
> > mmu_table_batch.
> > */
> > - smp_call_function(tlb_remove_table_smp_sync, NULL, 1);
> > + smp_call_function(tlb_remove_table_smp_sync, tlb->mm, 1);
> > __tlb_remove_table(table);
> > }
>
> But tlb_remove_table() doesn't always call
> tlb_remove_table_one(). Do
> the other paths through tlb_remove_table() do the right thing?
Urghhh, reading through the code it seems that
I got one case wrong.
The obvious cases, where tlb->mm->mm_users >= 2,
are both correct. The functions tlb_remove_table_one()
and tlb_table_flush() both get rid of lazy TLB users
of the MM.
However, there is one case where we don't but should:
/*
* When there's less then two users of this mm there cannot be
a
* concurrent page-table walk.
*/
if (atomic_read(&tlb->mm->mm_users) < 2) {
__tlb_remove_table(table);
return;
}
I guess the obvious fix is to call tlb_flush_remove_tables()
in the branch above. The first time it might shoot down a CPU
in lazy TLB mode, while the second time it is called that CPU
will have already switched to init_mm and no IPI is sent.
Alternatively, we could always do the batching, even when
mm_users is 1, and examine the bitmap with the other CPUs
less frequently in the exit path.
I can send in a patch for this tomorrow, or early next week,
depending on what other stuff comes up...
--
All Rights Reversed.
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next prev parent reply other threads:[~2018-08-16 5:32 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-16 19:03 [PATCH v6 0/7] x86,tlb,mm: make lazy TLB mode even lazier Rik van Riel
2018-07-16 19:03 ` [PATCH 1/7] mm: allocate mm_cpumask dynamically based on nr_cpu_ids Rik van Riel
2018-07-17 9:33 ` [tip:x86/mm] mm: Allocate the mm_cpumask (mm->cpu_bitmap[]) " tip-bot for Rik van Riel
2018-08-04 22:28 ` [PATCH 1/7] mm: allocate mm_cpumask " Guenter Roeck
2018-07-16 19:03 ` [PATCH 2/7] x86,tlb: leave lazy TLB mode at page table free time Rik van Riel
2018-07-17 9:34 ` [tip:x86/mm] x86/mm/tlb: Leave " tip-bot for Rik van Riel
2018-07-17 11:46 ` Peter Zijlstra
2018-07-25 1:00 ` Anders Roxell
2018-08-16 1:54 ` [PATCH 2/7] x86,tlb: leave " Andy Lutomirski
2018-08-16 5:31 ` Rik van Riel [this message]
2018-07-16 19:03 ` [PATCH 3/7] x86,mm: restructure switch_mm_irqs_off Rik van Riel
2018-07-17 9:34 ` [tip:x86/mm] x86/mm/tlb: Restructure switch_mm_irqs_off() tip-bot for Rik van Riel
2018-10-09 14:58 ` tip-bot for Rik van Riel
2018-07-16 19:03 ` [PATCH 4/7] x86,tlb: make lazy TLB mode lazier Rik van Riel
2018-07-17 9:35 ` [tip:x86/mm] x86/mm/tlb: Make " tip-bot for Rik van Riel
2018-07-17 11:33 ` Peter Zijlstra
2018-07-18 15:33 ` Rik van Riel
2018-07-18 16:00 ` Peter Zijlstra
[not found] ` <081E558D-DB34-4A18-A35C-896BC47F6EBA@surriel.com>
2018-07-18 18:23 ` Peter Zijlstra
2018-07-18 18:51 ` Rik van Riel
2018-07-19 9:13 ` Peter Zijlstra
2018-07-17 20:04 ` [PATCH 4/7] x86,tlb: make " Andy Lutomirski
[not found] ` <FF977B78-140F-4787-AA57-0EA934017D85@surriel.com>
2018-07-17 21:29 ` Andy Lutomirski
2018-07-17 22:05 ` Rik van Riel
2018-07-17 22:27 ` Andy Lutomirski
2018-07-18 20:58 ` Rik van Riel
2018-07-18 23:13 ` Andy Lutomirski
[not found] ` <B976CC13-D014-433A-83DE-F8DF9AB4F421@surriel.com>
2018-07-19 16:45 ` Andy Lutomirski
2018-07-19 17:04 ` Andy Lutomirski
2018-07-20 4:57 ` Benjamin Herrenschmidt
2018-07-20 8:30 ` Peter Zijlstra
2018-07-23 12:26 ` Rik van Riel
2018-07-24 16:33 ` Will Deacon
[not found] ` <CF849A07-B7CE-4DE9-8246-53AC5A53A705@surriel.com>
2018-07-19 17:18 ` Andy Lutomirski
2018-07-20 8:02 ` Vitaly Kuznetsov
2018-07-20 9:49 ` Peter Zijlstra
2018-07-20 10:18 ` Vitaly Kuznetsov
2018-07-20 9:32 ` Peter Zijlstra
2018-07-20 11:04 ` Peter Zijlstra
2018-07-16 19:03 ` [PATCH 5/7] x86,tlb: only send page table free TLB flush to lazy TLB CPUs Rik van Riel
2018-07-17 9:35 ` [tip:x86/mm] x86/mm/tlb: Only " tip-bot for Rik van Riel
2018-07-17 11:39 ` Peter Zijlstra
[not found] ` <1F8BDD25-864D-4105-B872-2109AA417454@surriel.com>
[not found] ` <24AA4367-22A1-450E-8F6A-3CBF39518384@surriel.com>
2018-07-18 16:19 ` Peter Zijlstra
2018-07-16 19:03 ` [PATCH 6/7] x86,mm: always use lazy TLB mode Rik van Riel
2018-07-17 9:36 ` [tip:x86/mm] x86/mm/tlb: Always " tip-bot for Rik van Riel
2018-10-09 14:58 ` tip-bot for Rik van Riel
2018-07-16 19:03 ` [PATCH 7/7] x86,switch_mm: skip atomic operations for init_mm Rik van Riel
2018-07-17 9:36 ` [tip:x86/mm] x86/mm/tlb: Skip atomic operations for 'init_mm' in switch_mm_irqs_off() tip-bot for Rik van Riel
-- strict thread matches above, loose matches on Subject: below --
2018-07-10 14:28 [PATCH v5 0/7] x86,tlb,mm: make lazy TLB mode even lazier Rik van Riel
2018-07-10 14:28 ` [PATCH 2/7] x86,tlb: leave lazy TLB mode at page table free time Rik van Riel
2018-07-06 21:56 [PATCH v4 0/7] x86,tlb,mm: make lazy TLB mode even lazier Rik van Riel
2018-07-06 21:56 ` [PATCH 2/7] x86,tlb: leave lazy TLB mode at page table free time Rik van Riel
2018-06-29 14:29 [PATCH v3 0/7] x86,tlb,mm: make lazy TLB mode even lazier Rik van Riel
2018-06-29 14:29 ` [PATCH 2/7] x86,tlb: leave lazy TLB mode at page table free time Rik van Riel
2018-06-29 16:39 ` Dave Hansen
2018-06-29 16:56 ` Rik van Riel
2018-06-20 19:56 [PATCH 0/7] x86,tlb,mm: make lazy TLB mode even lazier Rik van Riel
2018-06-20 19:56 ` [PATCH 2/7] x86,tlb: leave lazy TLB mode at page table free time Rik van Riel
2018-06-21 0:23 ` Rik van Riel
2018-06-22 14:58 ` Andy Lutomirski
2018-06-22 15:17 ` Rik van Riel
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