From: Nicholas Piggin <npiggin@gmail.com>
To: Nadav Amit <namit@vmware.com>, Peter Zijlstra <peterz@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
"linux-csky@vger.kernel.org" <linux-csky@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
linux-s390 <linux-s390@vger.kernel.org>,
Andy Lutomirski <luto@kernel.org>,
Mel Gorman <mgorman@techsingularity.net>,
Thomas Gleixner <tglx@linutronix.de>,
Will Deacon <will@kernel.org>, X86 ML <x86@kernel.org>,
Yu Zhao <yuzhao@google.com>
Subject: Re: [RFC 00/20] TLB batching consolidation and enhancements
Date: Tue, 02 Feb 2021 17:14:23 +1000 [thread overview]
Message-ID: <1612248111.g00kf5qxrp.astroid@bobo.none> (raw)
In-Reply-To: <YBf3sl3M+j3hJRoM@hirez.programming.kicks-ass.net>
Excerpts from Peter Zijlstra's message of February 1, 2021 10:44 pm:
> On Sun, Jan 31, 2021 at 07:57:01AM +0000, Nadav Amit wrote:
>> > On Jan 30, 2021, at 7:30 PM, Nicholas Piggin <npiggin@gmail.com> wrote:
>
>> > I'll go through the patches a bit more closely when they all come
>> > through. Sparc and powerpc of course need the arch lazy mode to get
>> > per-page/pte information for operations that are not freeing pages,
>> > which is what mmu gather is designed for.
>>
>> IIUC you mean any PTE change requires a TLB flush. Even setting up a new PTE
>> where no previous PTE was set, right?
In cases of increasing permissiveness of access, yes it may want to
update the "TLB" (read hash table) to avoid taking hash table faults.
But whatever the reason for the flush, there may have to be more
data carried than just the virtual address range and/or physical
pages.
If you clear out the PTE then you have no guarantee of actually being
able to go back and address the the in-memory or in-hardware translation
structures to update them, depending on what exact scheme is used
(powerpc probably could if all page sizes were the same, but THP or
64k/4k sub pages would throw a spanner in those works).
> These are the HASH architectures. Their hardware doesn't walk the
> page-tables, but it consults a hash-table to resolve page translations.
Yeah, it's very cool in a masochistic way.
I actually don't know if it's worth doing a big rework of it, as much
as I'd like to. Rather than just keep it in place and eventually
dismantling some of the go-fast hooks from core code if we can one day
deprecate it in favour of the much easier radix mode.
The whole thing is like a big steam train, years ago Paul and Ben and
Anton and co got the boiler stoked up and set all the valves just right
so it runs unbelievably well for what it's actually doing but look at it
the wrong way and the whole thing could blow up. (at least that's what
it feels like to me probably because I don't know the code that well).
Sparc could probably do the same, not sure about Xen. I don't suppose
vmware is intending to add any kind of paravirt mode related to this stuff?
Thanks,
Nick
prev parent reply other threads:[~2021-02-02 7:14 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-31 0:11 [RFC 00/20] TLB batching consolidation and enhancements Nadav Amit
2021-01-31 0:11 ` [RFC 01/20] mm/tlb: fix fullmm semantics Nadav Amit
2021-01-31 1:02 ` Andy Lutomirski
2021-01-31 1:19 ` Nadav Amit
2021-01-31 2:57 ` Andy Lutomirski
2021-02-01 7:30 ` Nadav Amit
2021-02-01 11:36 ` Peter Zijlstra
2021-02-02 9:32 ` Nadav Amit
2021-02-02 11:00 ` Peter Zijlstra
2021-02-02 21:35 ` Nadav Amit
2021-02-03 9:44 ` Will Deacon
2021-02-04 3:20 ` Nadav Amit
2021-01-31 0:11 ` [RFC 02/20] mm/mprotect: use mmu_gather Nadav Amit
2021-01-31 0:11 ` [RFC 03/20] mm/mprotect: do not flush on permission promotion Nadav Amit
2021-01-31 1:07 ` Andy Lutomirski
2021-01-31 1:17 ` Nadav Amit
2021-01-31 2:59 ` Andy Lutomirski
[not found] ` <7a6de15a-a570-31f2-14d6-a8010296e694@citrix.com>
2021-02-01 5:58 ` Nadav Amit
2021-02-01 15:38 ` Andrew Cooper
2021-01-31 0:11 ` [RFC 04/20] mm/mapping_dirty_helpers: use mmu_gather Nadav Amit
2021-01-31 0:11 ` [RFC 05/20] mm/tlb: move BATCHED_UNMAP_TLB_FLUSH to tlb.h Nadav Amit
2021-01-31 0:11 ` [RFC 06/20] fs/task_mmu: use mmu_gather interface of clear-soft-dirty Nadav Amit
2021-01-31 0:11 ` [RFC 07/20] mm: move x86 tlb_gen to generic code Nadav Amit
2021-01-31 18:26 ` Andy Lutomirski
2021-01-31 0:11 ` [RFC 08/20] mm: store completed TLB generation Nadav Amit
2021-01-31 20:32 ` Andy Lutomirski
2021-02-01 7:28 ` Nadav Amit
2021-02-01 16:53 ` Andy Lutomirski
2021-02-01 11:52 ` Peter Zijlstra
2021-01-31 0:11 ` [RFC 09/20] mm: create pte/pmd_tlb_flush_pending() Nadav Amit
2021-01-31 0:11 ` [RFC 10/20] mm: add pte_to_page() Nadav Amit
2021-01-31 0:11 ` [RFC 11/20] mm/tlb: remove arch-specific tlb_start/end_vma() Nadav Amit
2021-02-01 12:09 ` Peter Zijlstra
2021-02-02 6:41 ` Nicholas Piggin
2021-02-02 7:20 ` Nadav Amit
2021-02-02 9:31 ` Peter Zijlstra
2021-02-02 9:54 ` Nadav Amit
2021-02-02 11:04 ` Peter Zijlstra
2021-01-31 0:11 ` [RFC 12/20] mm/tlb: save the VMA that is flushed during tlb_start_vma() Nadav Amit
2021-02-01 12:28 ` Peter Zijlstra
2021-01-31 0:11 ` [RFC 13/20] mm/tlb: introduce tlb_start_ptes() and tlb_end_ptes() Nadav Amit
2021-01-31 9:57 ` Damian Tometzki
2021-01-31 10:07 ` Damian Tometzki
2021-02-01 7:29 ` Nadav Amit
2021-02-01 13:19 ` Peter Zijlstra
2021-02-01 23:00 ` Nadav Amit
2021-01-31 0:11 ` [RFC 14/20] mm: move inc/dec_tlb_flush_pending() to mmu_gather.c Nadav Amit
2021-01-31 0:11 ` [RFC 15/20] mm: detect deferred TLB flushes in vma granularity Nadav Amit
2021-02-01 22:04 ` Nadav Amit
2021-02-02 0:14 ` Andy Lutomirski
2021-02-02 20:51 ` Nadav Amit
2021-02-04 4:35 ` Andy Lutomirski
2021-01-31 0:11 ` [RFC 16/20] mm/tlb: per-page table generation tracking Nadav Amit
2021-01-31 0:11 ` [RFC 17/20] mm/tlb: updated completed deferred TLB flush conditionally Nadav Amit
2021-01-31 0:11 ` [RFC 18/20] mm: make mm_cpumask() volatile Nadav Amit
2021-01-31 0:11 ` [RFC 19/20] lib/cpumask: introduce cpumask_atomic_or() Nadav Amit
2021-01-31 0:11 ` [RFC 20/20] mm/rmap: avoid potential races Nadav Amit
2021-08-23 8:05 ` Huang, Ying
2021-08-23 15:50 ` Nadav Amit
2021-08-24 0:36 ` Huang, Ying
2021-01-31 0:39 ` [RFC 00/20] TLB batching consolidation and enhancements Andy Lutomirski
2021-01-31 1:08 ` Nadav Amit
2021-01-31 3:30 ` Nicholas Piggin
2021-01-31 7:57 ` Nadav Amit
2021-01-31 8:14 ` Nadav Amit
2021-02-01 12:44 ` Peter Zijlstra
2021-02-02 7:14 ` Nicholas Piggin [this message]
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