From: Peter Zijlstra <peterz@infradead.org>
To: Lance Yang <lance.yang@linux.dev>
Cc: akpm@linux-foundation.org, david@kernel.org,
dave.hansen@intel.com, dave.hansen@linux.intel.com,
ypodemsk@redhat.com, hughd@google.com, will@kernel.org,
aneesh.kumar@kernel.org, npiggin@gmail.com, tglx@linutronix.de,
mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com,
arnd@arndb.de, lorenzo.stoakes@oracle.com, ziy@nvidia.com,
baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com,
npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com,
baohua@kernel.org, shy828301@gmail.com, riel@surriel.com,
jannh@google.com, jgross@suse.com, seanjc@google.com,
pbonzini@redhat.com, boris.ostrovsky@oracle.com,
virtualization@lists.linux.dev, kvm@vger.kernel.org,
linux-arch@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, ioworker0@gmail.com
Subject: Re: [PATCH v4 0/3] targeted TLB sync IPIs for lockless page table walkers
Date: Mon, 2 Feb 2026 10:54:14 +0100 [thread overview]
Message-ID: <20260202095414.GE2995752@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20260202074557.16544-1-lance.yang@linux.dev>
On Mon, Feb 02, 2026 at 03:45:54PM +0800, Lance Yang wrote:
> When freeing or unsharing page tables we send an IPI to synchronize with
> concurrent lockless page table walkers (e.g. GUP-fast). Today we broadcast
> that IPI to all CPUs, which is costly on large machines and hurts RT
> workloads[1].
>
> This series makes those IPIs targeted. We track which CPUs are currently
> doing a lockless page table walk for a given mm (per-CPU
> active_lockless_pt_walk_mm). When we need to sync, we only IPI those CPUs.
> GUP-fast and perf_get_page_size() set/clear the tracker around their walk;
> tlb_remove_table_sync_mm() uses it and replaces the previous broadcast in
> the free/unshare paths.
I'm confused. This only happens when !PT_RECLAIM, because if PT_RECLAIM
__tlb_remove_table_one() actually uses RCU.
So why are you making things more expensive for no reason?
next prev parent reply other threads:[~2026-02-02 9:54 UTC|newest]
Thread overview: 41+ 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 11:37 ` kernel test robot
2026-02-03 23:49 ` kernel test robot
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
2026-02-25 20:11 ` Sean Christopherson
2026-02-26 11:37 ` Lance Yang
2026-02-26 18:24 ` Sean Christopherson
2026-03-01 6:56 ` Lance Yang
2026-02-02 9:54 ` Peter Zijlstra [this message]
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
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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