From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4B538D78776 for ; Fri, 19 Dec 2025 14:00:05 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id AE13E6B0088; Fri, 19 Dec 2025 09:00:04 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id A8F016B0089; Fri, 19 Dec 2025 09:00:04 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 991706B008A; Fri, 19 Dec 2025 09:00:04 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 8BC176B0088 for ; Fri, 19 Dec 2025 09:00:04 -0500 (EST) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 43C84B75E5 for ; Fri, 19 Dec 2025 14:00:04 +0000 (UTC) X-FDA: 84236379528.14.807BC49 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf10.hostedemail.com (Postfix) with ESMTP id 467E1C0013 for ; Fri, 19 Dec 2025 14:00:02 +0000 (UTC) Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=uxOhiDdn; spf=pass (imf10.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1766152802; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=B7ShADuvrWbzYt9sJu/TL9RJ7Nx42fawQ60gJTlh+Zc=; b=Vl7nefZAFXhChkIOPiN54PfeAsF7mIsR/s58zWXk8lcwLgigIKomIybNOY2xTrNLeCPtMn yzF1AUR4zZxdurIPdnygD1C75uJTWKe8g5bNBiSmXnVDz0olAohRMMcm891/YksDbrYTN+ bJNwYfyEn9ivcpG2/4PxiZ/n6XJOuWA= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1766152802; a=rsa-sha256; cv=none; b=3xAZhb37J9z7HoZfwhk2x7avmVytdM617Wrb1xEaqcDaVJpPX6EMz2jKO4ObClF88bErZf b9AtiEpzQxZtHGE9X0zNeSXC3mLrjCwE8N07lLgRa4gSNuQixzRcYB1bht0SHQkf7UJk/e hPB1GrDj9t0afkhsYt5pHFdFGBNACOc= ARC-Authentication-Results: i=1; imf10.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=uxOhiDdn; spf=pass (imf10.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 1712B41659; Fri, 19 Dec 2025 14:00:01 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 97208C4CEF1; Fri, 19 Dec 2025 13:59:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1766152800; bh=JWaw934JDfHKlA5sInvUxyZBA437IYufIDK3wABOHk0=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=uxOhiDdn5eNZtMqBuJSX4ivs/799liqB+DIx8GXZ5MehitAvEfEXlwvU0Z3T30ohy 7n/Tz90frJB1NvwJWfQ9cdDH7w1OK7iDT3YNnXrSPrCdhacEajjJscD8a5d/1lGyg2 b3E/Lo5yexghi+PacPVmA31lfSLDo0JR1YTUbKOFQBvuvWMmWzFunAWO2DaKiM12nd dNiN9smTTqUXTDkIa2G2nX9yBGpdDMiUjy+M6BYrVZf09gFJbjPRsQxMlIo5B4zJGj cEXr3TOPYu9w0FdmzB1aLgRpI74Uo8kfewMV6tRbVHr/zKVm7vdOonj0CIrzSsJ80E +pI+sn3yhU1+w== Message-ID: <3d9ce821-a39d-4164-a225-fcbe790ea951@kernel.org> Date: Fri, 19 Dec 2025 14:59:52 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 4/4] mm/hugetlb: fix excessive IPI broadcasts when unsharing PMD tables using mmu_gather From: "David Hildenbrand (Red Hat)" To: Harry Yoo Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, Will Deacon , "Aneesh Kumar K.V" , Andrew Morton , Nick Piggin , Peter Zijlstra , Arnd Bergmann , Muchun Song , Oscar Salvador , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Pedro Falcato , Rik van Riel , Laurence Oberman , Prakash Sangappa , Nadav Amit , stable@vger.kernel.org, Ryan Roberts , Catalin Marinas , Christophe Leroy References: <20251212071019.471146-1-david@kernel.org> <20251212071019.471146-5-david@kernel.org> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: idaeq4ntmegscfdmkrmrezukmrbdm1wx X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 467E1C0013 X-Rspam-User: X-HE-Tag: 1766152802-816243 X-HE-Meta: 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 WnT0S3Wf YohfGZSTqsBdzfKKMmzveHfpmSYfY1qymbcp4Rn7MsJNW8PA8BlVBj3RnItfc+Gjc+6TAFonRK99YQh2H8MnU4tjnR4U+AnUAzlxeLC8kIJuwfxE+KDPkoiu6t0WadamPYvCDDDXzd3ZTlP7X0TGSAITRX8IEPkFp3bqTbLQ8etq9pOhKN343NUqd4djJ0z7Q7HbmF1Fm75I8DmMf763Q4lNgekmNFQQzzfx2+5nfNi7iSm8Gf8UV2KVmAG3MBa6VUKY07IBvUx+Bf+kznlehH5mkkvinoz3WOX0l7VV4P6S1HAb4H2L8kiihyAIfkwuENFolzQmcePdZGBvlFhD15GRBqg5wopqjR1frdICOxwxkduATuc6Vgy8m5jcmLVuaGARB9hgavOyPM+yJ1WICweWWydlxIrJy3B9Wpl4QWBkBqlw= 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: On 12/19/25 14:52, David Hildenbrand (Red Hat) wrote: > On 12/19/25 13:37, Harry Yoo wrote: >> On Fri, Dec 12, 2025 at 08:10:19AM +0100, David Hildenbrand (Red Hat) wrote: >>> As reported, ever since commit 1013af4f585f ("mm/hugetlb: fix >>> huge_pmd_unshare() vs GUP-fast race") we can end up in some situations >>> where we perform so many IPI broadcasts when unsharing hugetlb PMD page >>> tables that it severely regresses some workloads. >>> >>> In particular, when we fork()+exit(), or when we munmap() a large >>> area backed by many shared PMD tables, we perform one IPI broadcast per >>> unshared PMD table. >>> >> >> [...snip...] >> >>> Fixes: 1013af4f585f ("mm/hugetlb: fix huge_pmd_unshare() vs GUP-fast race") >>> Reported-by: Uschakow, Stanislav" >>> Closes: https://lore.kernel.org/all/4d3878531c76479d9f8ca9789dc6485d@amazon.de/ >>> Tested-by: Laurence Oberman >>> Cc: >>> Signed-off-by: David Hildenbrand (Red Hat) >>> --- >>> include/asm-generic/tlb.h | 74 ++++++++++++++++++++++- >>> include/linux/hugetlb.h | 19 +++--- >>> mm/hugetlb.c | 121 ++++++++++++++++++++++---------------- >>> mm/mmu_gather.c | 7 +++ >>> mm/mprotect.c | 2 +- >>> mm/rmap.c | 25 +++++--- >>> 6 files changed, 179 insertions(+), 69 deletions(-) >>> >>> @@ -6522,22 +6511,16 @@ long hugetlb_change_protection(struct vm_area_struct *vma, >>> pte = huge_pte_clear_uffd_wp(pte); >>> huge_ptep_modify_prot_commit(vma, address, ptep, old_pte, pte); >>> pages++; >>> + tlb_remove_huge_tlb_entry(h, tlb, ptep, address); >>> } >>> >>> next: >>> spin_unlock(ptl); >>> cond_resched(); >>> } >>> - /* >>> - * There is nothing protecting a previously-shared page table that we >>> - * unshared through huge_pmd_unshare() from getting freed after we >>> - * release i_mmap_rwsem, so flush the TLB now. If huge_pmd_unshare() >>> - * succeeded, flush the range corresponding to the pud. >>> - */ >>> - if (shared_pmd) >>> - flush_hugetlb_tlb_range(vma, range.start, range.end); >>> - else >>> - flush_hugetlb_tlb_range(vma, start, end); >>> + >>> + tlb_flush_mmu_tlbonly(tlb); >>> + huge_pmd_unshare_flush(tlb, vma); >> >> Shouldn't we teach mmu_gather that it has to call > > I hope not :) In the worst case we could keep the > flush_hugetlb_tlb_range() in the !shared case in. Suboptimal but I am > sick and tired of dealing with this hugetlb mess. > > > Let me CC Ryan and Catalin for the arm64 pieces and Christophe on the > ppc pieces: See [1] where we convert away from some > flush_hugetlb_tlb_range() users to operate on mmu_gather using > * tlb_remove_huge_tlb_entry() for mremap() and mprotect(). Before we > would only use it in __unmap_hugepage_range(). > * tlb_flush_pmd_range() for unsharing of shared PMD tables. We already > used that in one call path. To clarify, powerpc does not select ARCH_WANT_HUGE_PMD_SHARE, so the second change does not apply to ppc. -- Cheers David