From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5773B606A331 for ; Fri, 13 Nov 2026 18:36:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=fdd8SQJS Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 132F7112598; Fri, 13 Nov 2026 18:36:11 +0000 (UTC) Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by gabe.freedesktop.org (Postfix) with ESMTPS id 355F510EC8A; Fri, 13 Nov 2026 18:36:05 +0000 (UTC) Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id D17EA40B81; Fri, 13 Nov 2026 18:36:04 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0618B1F000C4; Fri, 13 Nov 2026 18:36:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794594964; bh=Nr1sabwRiVAnVE1Zz6waN9h+CZcSzSFjuvr4+7jGL1A=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=fdd8SQJSLXHHGJM+CTe5q0eusqLo4/Yvj6Hy+N/Kdr4TpdX80s8pu9YqSQPtU1RAo F0uIHpulEmevf26g2P+5GP91AAQGtijOfX2d/nR0pLfTIFybtsfyCfdnV9vddJZ6GB cMn/SiRohtSr3ditXEnGa+7K0U5oaJWNnZxfGSRnYEHmTTLDzEasOu+ss9NXQnLLs1 9ke0TAlhkOQ1EeRyY1uWxLihthGWstqA5D+7kFOmW2MwY9m318XGHjKXBcLBRZFU3z +yF0IH376OzpLjOpO3042tb2yP9n9VWCcQo5XB+T8UNEaSQC8v6VqzbdHx50/oXw8a 6/jn9/5CMHqxg== Message-ID: Date: Fri, 13 Nov 2026 19:27:56 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/hmm: skip NUMA balancing on protnone faults To: Matthew Auld , linux-mm@kvack.org Cc: dri-devel@lists.freedesktop.org, intel-xe@lists.freedesktop.org, =?UTF-8?Q?Thomas_Hellstr=C3=B6m?= , Matthew Brost , =?UTF-8?Q?Mika_Penttil=C3=A4?= , Leon Romanovsky , Jason Gunthorpe References: <20261112-numa-v1-1-ad9cbca8f49a@intel.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-BeenThere: intel-xe@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel Xe graphics driver List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Intel-xe" X-Spam-Status: No, score=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 11/13/26 17:25, Matthew Auld wrote: > When automatic NUMA balancing marks a PTE or PMD as protnone > (PAGE_NONE), hmm_pte_need_fault() requests a fault to restore access > permissions, including _PAGE_RW when write access is needed. > > Calling handle_mm_fault() from hmm_do_fault() currently triggers NUMA > balancing in do_numa_page() and do_huge_pmd_numa_page(). When > hmm_range_fault() runs from a device driver or kworker context (such as > a GPU SVM or userptr rebind worker), folios get migrated toward the CPU > node executing the remote fault. > > Also, each folio migration invokes try_to_migrate_one() -> > mmu_notifier_invalidate_range_start(), which invalidates the > caller's mmu_interval_notifier while holding mmap_lock. That causes > hmm_range_fault() to abort with -EBUSY after every 2 MiB PMD and exhaust > its retry timeout on large buffers, which has been observed with large > imported Xe userptr buffers. > > Add FAULT_FLAG_NO_NUMA and set it in hmm_do_fault() so protnone entries > restore PTE/PMD permissions in-place without performing NUMA balancing, > matching GUP's default !FOLL_HONOR_NUMA_FAULT behaviour. Ehm, that's not how it works. GUP will not trigger a "special" fault and will try not triggering a fault and not restore permissions. It will try continuing, leaving the protnone pte as it is. See gup_can_follow_protnone(). For read-only access that should always work. For write-access we always trigger an ordinary fault and do NUMA migration etc. So FAULT_FLAG_NO_NUMA is doing something completely different and I don't agree with it. -- Cheers, David