From: Dave Hansen <dave.hansen@linux.intel.com>
To: Rik van Riel <riel@surriel.com>, linux-kernel@vger.kernel.org
Cc: x86@kernel.org, luto@kernel.org, mingo@kernel.org,
kernel-team@fb.com, tglx@linutronix.de, efault@gmx.de,
songliubraving@fb.com, hpa@zytor.com
Subject: Re: [PATCH 2/7] x86,tlb: leave lazy TLB mode at page table free time
Date: Fri, 29 Jun 2018 09:39:00 -0700 [thread overview]
Message-ID: <75090b06-fd6f-eeaa-4cb8-8373673c8a5d@linux.intel.com> (raw)
In-Reply-To: <20180629142918.26601-3-riel@surriel.com>
On 06/29/2018 07:29 AM, Rik van Riel wrote:
> The latter problem can be prevented in two ways. The first is to
> always send a TLB shootdown IPI to CPUs in lazy TLB mode, while
> the second one is to only send the TLB shootdown at page table
> freeing time.
I've read this a few times, and I keep having to remind myself why we
"always send a TLB shootdown IPI to CPUs in lazy TLB mode". It's not
strictly CPUs in lazy TLB mode, right? It's just the one that are in
lazy TLB mode _and_ using the mm from which we are freeing page tables.
If you revise these again, would it make sense to add a little blurb like:
CPUs in lazy TLB mode are using the "wrong" page tables,
generally from a process's mm while running true kernel code
like the idle task. This is just as problematic when freeing
page tables from that mm as a real non-lazy user of the page
tables would be.
> The second should result in fewer IPIs, since operationgs like
> mprotect and madvise are very common with some workloads, but
> do not involve page table freeing. Also, on munmap, batching
> of page table freeing covers much larger ranges of virtual
> memory than the batching of unmapped user pages.
Doesn't this also result in fewer IPIs because it *removes* the
processor from the mm_cpumask(mm) and won't send IPIs to it any more?
As it stood before, we'd IPI a lazy CPU over and over, but this way we
just do it once, switch to another mm, and never touch for this mm again
(unless that CPU becomes non-lazy and switches to that mm again).
next prev parent reply other threads:[~2018-06-29 16:39 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
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 1/7] mm: allocate mm_cpumask dynamically based on nr_cpu_ids Rik van Riel
2018-06-30 4:30 ` kbuild test robot
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 [this message]
2018-06-29 16:56 ` Rik van Riel
2018-06-29 14:29 ` [PATCH 3/7] x86,mm: restructure switch_mm_irqs_off Rik van Riel
2018-06-29 16:49 ` Dave Hansen
2018-06-29 14:29 ` [PATCH 4/7] x86,tlb: make lazy TLB mode lazier Rik van Riel
2018-06-29 17:05 ` Dave Hansen
2018-06-29 17:29 ` Rik van Riel
2018-06-29 14:29 ` [PATCH 5/7] x86,tlb: only send page table free TLB flush to lazy TLB CPUs Rik van Riel
2018-07-07 12:26 ` Mike Galbraith
2018-07-07 13:39 ` Mike Galbraith
2018-07-07 21:21 ` Rik van Riel
2018-06-29 14:29 ` [PATCH 6/7] x86,mm: always use lazy TLB mode Rik van Riel
2018-06-29 14:29 ` [PATCH 7/7] x86,switch_mm: skip atomic operations for init_mm Rik van Riel
2018-06-29 17:06 ` [PATCH v3 0/7] x86,tlb,mm: make lazy TLB mode even lazier Dave Hansen
-- strict thread matches above, loose matches on Subject: below --
2018-07-16 19:03 [PATCH v6 " Rik van Riel
2018-07-16 19:03 ` [PATCH 2/7] x86,tlb: leave lazy TLB mode at page table free time Rik van Riel
2018-08-16 1:54 ` Andy Lutomirski
2018-08-16 5:31 ` Rik van Riel
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
2018-06-20 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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