From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 117C433D4F0; Tue, 6 Jan 2026 15:19:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767712761; cv=none; b=uqUxY/IbEJvg1miGKjVxShsfb5lTS8/UgPEVcnFu2Eo1RrUx9Q4JeZBfRpsE3NRh72hv/IL0V+XUozOceXOpVq5fQA8efuWmLRfayKr5SiQAHcJnv1gsKrqnIXoaoP/zS2ojbKOrwdmkynAB/Zapcr3svJcCEMjfQ1a+YQEb7z0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767712761; c=relaxed/simple; bh=PQWjEY27AuDHc3U5eemh0TiBpvWBZ7jdK/tSG6xBxCE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LKSFCWJ/82BzspAUceHZNWss+PDb0BXTbu8LkhrBWBV49NhortwBXlt6Lc9GDGr7mm9EjP3OUL4QOCTfqpFTm0GSpRBUkUiXyTlLLRZoK64OLM3/1C2jDTFnOKkdub+rjoMjBZGnosm1DWwInAxRJbkXkKlHQAzom1Unet0NfXU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZzFBdx/W; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ZzFBdx/W" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1C849C116C6; Tue, 6 Jan 2026 15:19:12 +0000 (UTC) DKIM-Signature: v=1; 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 > > 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