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From: Christoph Hellwig <hch@lst.de>
To: Felix Kuehling <felix.kuehling@amd.com>
Cc: "Sierra Guiza, Alejandro (Alex)" <alex.sierra@amd.com>,
	Ralph Campbell <rcampbell@nvidia.com>,
	akpm@linux-foundation.org, linux-mm@kvack.org,
	linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org,
	Theodore Ts'o <tytso@mit.edu>,
	amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	hch@lst.de, jgg@nvidia.com, jglisse@redhat.com
Subject: Re: [PATCH v6 02/13] mm: remove extra ZONE_DEVICE struct page refcount
Date: Fri, 20 Aug 2021 06:40:12 +0200	[thread overview]
Message-ID: <20210820044012.GA26960@lst.de> (raw)
In-Reply-To: <40d4a39e-e874-4ba3-e9bc-42015f0383fa@amd.com>

On Thu, Aug 19, 2021 at 03:59:56PM -0400, Felix Kuehling wrote:
> I got lost trying to understand how DAX counts page references and how
> the PTE_SPECIAL option affects that. Theodore, can you help with this?
> Is there an easy way to test without CONFIG_ARCH_HAS_PTE_SPECIAL on x86,
> or do we need to test on a CPU architecture that doesn't support this
> feature?

I think the right answer is to simplify disallow ZONE_DEVICE pages
if ARCH_HAS_PTE_SPECIAL is not supported.  ARCH_HAS_PTE_SPECIAL is
supported by all modern architecture ports than can make use of
ZONE_DEVICE / dev_pagemap, so we can avoid this pocket of barely
testable code entirely:


diff --git a/mm/Kconfig b/mm/Kconfig
index 40a9bfcd5062e1..2823bbfd1c8c70 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -775,6 +775,7 @@ config ZONE_DMA32
 
 config ZONE_DEVICE
 	bool "Device memory (pmem, HMM, etc...) hotplug support"
+	depends on ARCH_HAS_PTE_SPECIAL
 	depends on MEMORY_HOTPLUG
 	depends on MEMORY_HOTREMOVE
 	depends on SPARSEMEM_VMEMMAP

  reply	other threads:[~2021-08-20 13:05 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-13  6:31 [PATCH v6 00/13] Support DEVICE_GENERIC memory in migrate_vma_* Alex Sierra
2021-08-13  6:31 ` [PATCH v6 01/13] ext4/xfs: add page refcount helper Alex Sierra
2021-08-15  9:01   ` Christoph Hellwig
2021-08-13  6:31 ` [PATCH v6 02/13] mm: remove extra ZONE_DEVICE struct page refcount Alex Sierra
2021-08-15 15:37   ` Christoph Hellwig
2021-08-15 20:40     ` John Hubbard
2021-08-16 18:56       ` Felix Kuehling
2021-08-20  6:33       ` Jerome Glisse
2021-08-18  0:01   ` Ralph Campbell
2021-08-18  0:35     ` Felix Kuehling
2021-08-18 19:28       ` Ralph Campbell
2021-08-19 18:00         ` Sierra Guiza, Alejandro (Alex)
2021-08-19 19:59           ` Felix Kuehling
2021-08-20  4:40             ` Christoph Hellwig [this message]
2021-08-20  7:17           ` Jerome Glisse
2021-08-20  4:56         ` Christoph Hellwig
2021-08-13  6:31 ` [PATCH v6 03/13] kernel: resource: lookup_resource as exported symbol Alex Sierra
2021-08-13  6:31 ` [PATCH v6 04/13] drm/amdkfd: add SPM support for SVM Alex Sierra
2021-08-15  9:10   ` Christoph Hellwig
2021-08-16 18:54     ` Felix Kuehling
2021-08-17  5:47       ` Christoph Hellwig
2021-08-13  6:31 ` [PATCH v6 05/13] drm/amdkfd: generic type as sys mem on migration to ram Alex Sierra
2021-08-15 15:38   ` Christoph Hellwig
2021-08-16 19:53     ` Sierra Guiza, Alejandro (Alex)
2021-08-16 22:06       ` Zeng, Oak
2021-08-17  0:42         ` Felix Kuehling
2021-08-17  5:49       ` Christoph Hellwig
2021-08-13  6:31 ` [PATCH v6 06/13] include/linux/mm.h: helpers to check zone device generic type Alex Sierra
2021-08-15  9:16   ` Christoph Hellwig
2021-08-13  6:31 ` [PATCH v6 07/13] mm: add generic type support to migrate_vma helpers Alex Sierra
2021-08-15  9:19   ` Christoph Hellwig
2021-08-13  6:31 ` [PATCH v6 08/13] mm: call pgmap->ops->page_free for DEVICE_GENERIC pages Alex Sierra
2021-08-15 15:40   ` Christoph Hellwig
2021-08-16 19:00     ` Felix Kuehling
2021-08-17  5:50       ` Christoph Hellwig
2021-08-17 15:44         ` Felix Kuehling
2021-08-20  5:05           ` Christoph Hellwig
2021-08-20  7:24             ` Jerome Glisse
2021-08-13  6:31 ` [PATCH v6 09/13] lib: test_hmm add ioctl to get zone device type Alex Sierra
2021-08-13  6:31 ` [PATCH v6 10/13] lib: test_hmm add module param for " Alex Sierra
2021-08-13  6:31 ` [PATCH v6 11/13] lib: add support for device generic type in test_hmm Alex Sierra
2021-08-13  6:31 ` [PATCH v6 12/13] tools: update hmm-test to support device generic type Alex Sierra
2021-08-13  6:31 ` [PATCH v6 13/13] tools: update test_hmm script to support SP config Alex Sierra

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