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 21CB2D6ACFB for ; Thu, 18 Dec 2025 12:52:57 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 8ADCB6B0088; Thu, 18 Dec 2025 07:52:56 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 85B116B0089; Thu, 18 Dec 2025 07:52:56 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 75DD16B008A; Thu, 18 Dec 2025 07:52:56 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 656126B0088 for ; Thu, 18 Dec 2025 07:52:56 -0500 (EST) Received: from smtpin22.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id DB3655546E for ; Thu, 18 Dec 2025 12:52:55 +0000 (UTC) X-FDA: 84232581510.22.FED70C1 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf20.hostedemail.com (Postfix) with ESMTP id 1C92E1C0005 for ; Thu, 18 Dec 2025 12:52:53 +0000 (UTC) Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=jvIZGS7s; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf20.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1766062374; a=rsa-sha256; cv=none; b=2jBJrfPzY6KSDSx121HKn5ApbN08GSijGVYzteBgjO+3FSssqQomnnU4t8Abnr/Fl1a6Hu fpJzUyJyE7s2A0vLMidgoe3TESsQTVHiWFHRrFPRDWgL5Wb4Ww95MyPhLyN0VpmFn8mTeA UbH6I07GPe7vd57sBfBw3iZYaU1SoYw= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=jvIZGS7s; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf20.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1766062374; 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=pwuCcAbyOJ7qnpq5z4Eo0OHX/cjx0MWwc54BwLt4sIE=; b=C3Wn7a0hhPb7pCselB5KZ11lzbTiqMrWCvZl5cI2TH3uYczFDXH9/Fva5l583Fu+G3SdCp E+PkTXgzHGZV6/Xb9ZB52NWgvJALTwjIENL8LbPKFB3A7NjRU8N9E2llZv2cx4G9KOFl+q I8KGQx99dSb3vB+b9PzPYGGx89YVwKI= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id BE8FB42BBA; Thu, 18 Dec 2025 12:52:52 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E38B5C4CEFB; Thu, 18 Dec 2025 12:52:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1766062372; bh=4PcjO3AAv5DkTbbnZnTkTeokRBEqI4f7EfDmqqxEmUw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=jvIZGS7s+QzMFSaoNVysN2TYamdUXJ6Jl2Hq+DlBuaQ9w0DqxheKIKHVn+qEvL9CF MXJDMfIJBmMDBzJJpSSiuu09BHn41tV9pd5zPSsNpTja8mk2kIpPLDz8e4l3M8N840 EPq6EDrm+IhG7D6GU/Vve8TalEjb0lT0M/XQ+LbSAJvC0SPXXs5cvIdoORRCayMpE7 acTa7HIVMGHHyDbSKEbYR/MmJXmAGB6eIjQ/cFcSuibOY2j2GTqsQn3IoGwubJuxFa aKjPd+GnmBgBfCGQ3piUSHEfdmomASe8Y68QKAD6P74ib5NrZXSE7Bu0rw94XhWYRP BUePV3JMHVoIQ== Message-ID: Date: Thu, 18 Dec 2025 13:52:45 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 4/4] mm/hugetlb: fix excessive IPI broadcasts when unsharing PMD tables using mmu_gather To: Lorenzo Stoakes 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" , Vlastimil Babka , Jann Horn , Pedro Falcato , Rik van Riel , Harry Yoo , Laurence Oberman , Prakash Sangappa , Nadav Amit , stable@vger.kernel.org References: <20251205213558.2980480-1-david@kernel.org> <20251205213558.2980480-5-david@kernel.org> <9ac7c53e-04ae-49f3-976d-44d1e29587d1@kernel.org> <07e8b94e-b4a1-4541-84ed-a5d57058d5a1@lucifer.local> <937a4525-910d-4596-a9c4-29e47ca53667@kernel.org> <4037214b-d1c6-4e0b-ad9d-6722aea7aba9@lucifer.local> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <4037214b-d1c6-4e0b-ad9d-6722aea7aba9@lucifer.local> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 1C92E1C0005 X-Stat-Signature: id6175j9kazoxsicerp84im6wnt7cd7w X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1766062373-810167 X-HE-Meta: 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 PAvHi+ac 4xe/UXdmpyWAMELidzDQ/2UWJ8C5e1f+t7x1lUIvxe3lLtHAYWZSq7DlHkm9xIgJ4I1hj6xalUTvtsN4epsIRopSDwbwrZMqL51lbwXF5fEHpzNEenKCGzyXidlqnYfi7BIGwYzWCsPniiIiof2sm9Cs9q5TnyWlXEaQSFBcghxzFPicE6qSKlr/7J2heMbfeVgdOgtum66/uuZKF9bHyUjnXm/72MP0GGvbEDw2BOxOQzcJ+ZGJ3YEAb6ihL1RxK6tADaAriWBpqFJqTE2QtKrtbZbG18uGHUHo0bXlPgrOlW1TChJKrjfjUDynYzSie5Yb8Dlu6V5plvTQJ+Z5xoR9GjA== 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: >>> >>> Isn't really the correct comment here that ranges that previously mapped the >>> shared pages might no longer, so we must clear the TLB? I may be missing >>> something :) >> >> There are cases where we defer flushing the TLB until we dropped all (exclusive) locks. >> In particular, MADV_DONTNEED does that in some cases, essentially deferring the flush >> to the tlb_finish_mmu(). >> >> free_pgtables() will also defer the flush, performing the TLB flush during tlb_finish_mmu(), >> before >> >> The point is (as I tried to make clear in the comment), for unsharing we have no control >> whenn the page table gets freed after we drop the lock. >> >> So we must flush the TLB now and cannot defer it like we do in the other cases. > > Yeah I guess because of the above - that is - other users may unshare for their > CPUs but not unshare for ours? Yes :) It's all very complicated, therefore I decided to rather add more comments describing what we depend on. -- Cheers David