From: Dave Hansen <dave.hansen@intel.com>
To: Lance Yang <lance.yang@linux.dev>, akpm@linux-foundation.org
Cc: will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com,
peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com,
bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org,
hpa@zytor.com, arnd@arndb.de, david@kernel.org,
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, ioworker0@gmail.com, shy828301@gmail.com,
riel@surriel.com, jannh@google.com, linux-arch@vger.kernel.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 0/3] skip redundant TLB sync IPIs
Date: Tue, 30 Dec 2025 20:26:28 -0800 [thread overview]
Message-ID: <f81b98e5-87c0-4c21-9a75-ad5f9b6af6aa@intel.com> (raw)
In-Reply-To: <20251229145245.85452-1-lance.yang@linux.dev>
On 12/29/25 06:52, Lance Yang wrote:
...
> This series introduces a way for architectures to indicate their TLB flush
> already provides full synchronization, allowing the redundant IPI to be
> skipped. For now, the optimization is implemented for x86 first and applied
> to all page table operations that free or unshare tables.
I really don't like all the complexity here. Even on x86, there are
three or more ways of deriving this. Having the pv_ops check the value
of another pv op is also a bit unsettling.
That said, complexity can be worth it with sufficient demonstrated
gains. But:
> When unsharing hugetlb PMD page tables or collapsing pages in khugepaged,
> we send two IPIs: one for TLB invalidation, and another to synchronize
> with concurrent GUP-fast walkers.
Those aren't exactly hot paths. khugepaged is fundamentally rate
limited. I don't think unsharing hugetlb PMD page tables just is all
that common either.
What kind of end user benefit is there to justify the complexity?
next prev parent reply other threads:[~2025-12-31 4:26 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-12-29 14:52 Lance Yang
2025-12-29 14:52 ` [PATCH v2 1/3] mm/tlb: allow architectures to " Lance Yang
2025-12-29 15:00 ` Lance Yang
2025-12-29 15:01 ` [PATCH v2 0/3] " Lance Yang
2025-12-30 20:31 ` [PATCH v2 1/3] mm/tlb: allow architectures to " David Hildenbrand (Red Hat)
2025-12-31 2:29 ` Lance Yang
2025-12-29 14:52 ` [PATCH v2 2/3] x86/mm: implement redundant IPI elimination for page table operations Lance Yang
2025-12-29 14:52 ` [PATCH v2 3/3] mm: embed TLB flush IPI check in tlb_remove_table_sync_one() Lance Yang
2025-12-30 20:33 ` David Hildenbrand (Red Hat)
2025-12-31 3:03 ` Lance Yang
2025-12-31 4:26 ` Dave Hansen [this message]
2025-12-31 12:33 ` [PATCH v2 0/3] skip redundant TLB sync IPIs David Hildenbrand (Red Hat)
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