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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767712760; bh=PQWjEY27AuDHc3U5eemh0TiBpvWBZ7jdK/tSG6xBxCE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ZzFBdx/WI2GjYmhcvi6yp9/4UwfmyCrys7P4UZIgj9FaT0LKyStePM0eQWcUtCvvD /V+gKQvG7a5yrjBvfP3OIZyuMzZcMET1RTxKDveQdPqP4J0DZItzZPPXMiwZqRJxTH ltE0xzEPK4GVmb4gMdVhyH8bNy3BF0lQYPQpov9PLICaPs60edviHqk09OlDoH0xPd a5h8A4YKZAZYXLg467JE6rI21qfDDc21DmskYYRK8VOMlItxTnVkmGU0o2NZ95NM05 pmZzeKuBl5AVnS7gEx1hfB0qvpQtQU6tW2wcirPpQZSWcVxB4fWJg52P/EadhVBR7F KN8vizOZoWdiA== Message-ID: Date: Tue, 6 Jan 2026 16:19:10 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RESEND v3 1/2] mm/tlb: skip redundant IPI when TLB flush already synchronized To: Lance Yang , akpm@linux-foundation.org Cc: dave.hansen@intel.com, dave.hansen@linux.intel.com, will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, peterz@infradead.org, 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, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ioworker0@gmail.com References: <20260106120303.38124-1-lance.yang@linux.dev> <20260106120303.38124-2-lance.yang@linux.dev> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: E7ED4C0013 X-Rspamd-Server: rspam10 X-Stat-Signature: pg8o4mncfzrcp1g8z87a88mt9bdhsksm X-HE-Tag: 1767712761-879577 X-HE-Meta: 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 HiL0vVb5 ikGnLWemtNZHj7Q7DG/8lwIOoWMpHsPs2oUp7finurjHXeLOMelwA6zj8J8h5q+3owTJuFnauWSLZRjCbm6gIk9bTJ6KiExtQ5ExmIm1iRb/2xq815KX7zZfE6xenhccobdBTS1G6a4eGvdrjUPzsxWeakR6wB0rx+FTmPqtAs4/QQion7yZhcAuqB1zbfrMVSMuRyjLfvLENHci3dwG4/DEaTs6Vba9XnA3XtkAGvbFhqK670iJ/vp2I7OM25kQErokW X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > > static void tlb_table_flush(struct mmu_gather *tlb) > @@ -367,7 +378,7 @@ void tlb_remove_table(struct mmu_gather *tlb, void *table) > *batch = (struct mmu_table_batch *)__get_free_page(GFP_NOWAIT); > if (*batch == NULL) { > tlb_table_invalidate(tlb); > - tlb_remove_table_one(table); > + tlb_remove_table_one(table, tlb); > return; > } > (*batch)->nr = 0; > @@ -427,6 +438,7 @@ static void __tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, > tlb->vma_pfn = 0; > > tlb->fully_unshared_tables = 0; > + tlb->tlb_flush_sent_ipi = 0; > __tlb_reset_range(tlb); > inc_tlb_flush_pending(tlb->mm); > } But when would we have to reset tlb->tlb_flush_sent_ipi = 0 later? That's where it gets tricky. Just imagine the MMU gather gets reused later. Also, + if (info->freed_tables && info->tlb) + info->tlb->tlb_flush_sent_ipi = true; in native_flush_tlb_multi() misses the fact that we have different flushing types for removed/unshared tables vs. other flush. So this approach more here certainly gets more complicated and error prone. tlb_table_flush_implies_ipi_broadcast() was clearer in that regard: if you flushed the TLB after removing /unsharing tables, the IPI for handling page tables can be skipped. It's on the code flow to assure that. What could work is tracking "tlb_table_flush_sent_ipi" really when we are flushing the TLB for removed/unshared tables, and maybe resetting it ... I don't know when from the top of my head. v2 was simpler IMHO. -- Cheers David