From: Dave Hansen <dave.hansen@intel.com>
To: Lance Yang <lance.yang@linux.dev>,
"David Hildenbrand (Arm)" <david@kernel.org>,
Peter Zijlstra <peterz@infradead.org>
Cc: Liam.Howlett@oracle.com, akpm@linux-foundation.org,
aneesh.kumar@kernel.org, arnd@arndb.de, baohua@kernel.org,
baolin.wang@linux.alibaba.com, boris.ostrovsky@oracle.com,
bp@alien8.de, dave.hansen@linux.intel.com, dev.jain@arm.com,
hpa@zytor.com, hughd@google.com, ioworker0@gmail.com,
jannh@google.com, jgross@suse.com, kvm@vger.kernel.org,
linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, lorenzo.stoakes@oracle.com, mingo@redhat.com,
npache@redhat.com, npiggin@gmail.com, pbonzini@redhat.com,
riel@surriel.com, ryan.roberts@arm.com, seanjc@google.com,
shy828301@gmail.com, tglx@linutronix.de,
virtualization@lists.linux.dev, will@kernel.org, x86@kernel.org,
ypodemsk@redhat.com, ziy@nvidia.com
Subject: Re: [PATCH v4 0/3] targeted TLB sync IPIs for lockless page table
Date: Thu, 5 Feb 2026 07:41:16 -0800 [thread overview]
Message-ID: <647cbe2e-a034-4a75-9492-21ea1708eccc@intel.com> (raw)
In-Reply-To: <c985a8ed-37ad-415e-b7b4-18a66b4da3fe@linux.dev>
On 2/5/26 07:31, Lance Yang wrote:
> On 2026/2/5 23:09, Dave Hansen wrote:
>> On 2/5/26 07:01, Lance Yang wrote:
>>> So for now, neither approach looks good: tracking on the read side adss
>>> cost to GUP-fast, and syncing on the write side e.g. synchronize_rcu()
>>> is too slow on large systems.
>>
>> Which of the writers truly *need* synchronize_rcu()?
>>
>> What are they doing with the memory that they can't move forward unless
>> it's quiescent *now*?
>
> Without IPIs or synchronize_rcu(), IIUC, we have no way to know if there
> are ongoing concurrent lockless page-table walks — the walkers just disable
> IRQs and walk.
Yeah, but one aim of RCU is ensuring that readers see valid data but not
necessarily the most up to date data.
Are there cases where ongoing concurrent lockless page-table walks need
to see the writes and they can't tolerate seeing valid but slightly
stale data?
Don't forget that we also have pesky concurrent lockless page-table
walkers called CPUs. They're extra pesky in that they don't even stop
for IPIs. ;)
next prev parent reply other threads:[~2026-02-05 15:41 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-02 7:45 [PATCH v4 0/3] targeted TLB sync IPIs for lockless page table walkers Lance Yang
2026-02-02 7:45 ` [PATCH v4 1/3] mm: use targeted IPIs for TLB sync with " Lance Yang
2026-02-02 9:42 ` Peter Zijlstra
2026-02-02 12:14 ` Lance Yang
2026-02-02 12:51 ` Peter Zijlstra
2026-02-02 13:23 ` Lance Yang
2026-02-02 13:42 ` Peter Zijlstra
2026-02-02 14:28 ` Lance Yang
2026-02-02 16:20 ` Dave Hansen
2026-02-02 7:45 ` [PATCH v4 2/3] mm: switch callers to tlb_remove_table_sync_mm() Lance Yang
2026-02-02 7:45 ` [PATCH v4 3/3] x86/tlb: add architecture-specific TLB IPI optimization support Lance Yang
2026-02-02 9:54 ` [PATCH v4 0/3] targeted TLB sync IPIs for lockless page table walkers Peter Zijlstra
2026-02-02 11:00 ` [PATCH v4 0/3] targeted TLB sync IPIs for lockless page table Lance Yang
2026-02-02 12:50 ` Peter Zijlstra
2026-02-02 12:58 ` Lance Yang
2026-02-02 13:07 ` Lance Yang
2026-02-02 13:37 ` Peter Zijlstra
2026-02-02 14:37 ` Lance Yang
2026-02-02 15:09 ` Peter Zijlstra
2026-02-02 15:52 ` Lance Yang
2026-02-05 13:25 ` David Hildenbrand (Arm)
2026-02-05 15:01 ` Lance Yang
2026-02-05 15:05 ` David Hildenbrand (Arm)
2026-02-05 15:28 ` Lance Yang
2026-02-05 15:09 ` Dave Hansen
2026-02-05 15:31 ` Lance Yang
2026-02-05 15:41 ` Dave Hansen [this message]
2026-02-05 16:30 ` Lance Yang
2026-02-05 16:46 ` David Hildenbrand (Arm)
2026-02-05 16:48 ` Matthew Wilcox
2026-02-05 17:06 ` David Hildenbrand (Arm)
2026-02-05 18:36 ` Dave Hansen
2026-02-05 22:49 ` David Hildenbrand (Arm)
2026-02-05 21:30 ` David Hildenbrand (Arm)
2026-02-05 17:00 ` Dave Hansen
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