From: Jason Gunthorpe <jgg@ziepe.ca>
To: Christoph Hellwig <hch@lst.de>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Dan Williams" <dan.j.williams@intel.com>,
"Felix Kuehling" <Felix.Kuehling@amd.com>,
"Alex Deucher" <alexander.deucher@amd.com>,
"Christian König" <christian.koenig@amd.com>,
"Pan, Xinhui" <Xinhui.Pan@amd.com>,
"Ben Skeggs" <bskeggs@redhat.com>,
"Karol Herbst" <kherbst@redhat.com>,
"Lyude Paul" <lyude@redhat.com>,
"Alistair Popple" <apopple@nvidia.com>,
"Logan Gunthorpe" <logang@deltatee.com>,
"Ralph Campbell" <rcampbell@nvidia.com>,
linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org,
dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org,
nvdimm@lists.linux.dev, linux-mm@kvack.org
Subject: Re: [PATCH 7/8] mm: remove the extra ZONE_DEVICE struct page refcount
Date: Mon, 7 Feb 2022 15:21:55 -0400 [thread overview]
Message-ID: <20220207192155.GB49147@ziepe.ca> (raw)
In-Reply-To: <20220207063249.1833066-8-hch@lst.de>
On Mon, Feb 07, 2022 at 07:32:48AM +0100, Christoph Hellwig wrote:
> ZONE_DEVICE struct pages have an extra reference count that complicates
> the code for put_page() and several places in the kernel that need to
> check the reference count to see that a page is not being used (gup,
> compaction, migration, etc.). Clean up the code so the reference count
> doesn't need to be treated specially for ZONE_DEVICE pages.
>
> Note that this excludes the special idle page wakeup for fsdax pages,
> which still happens at refcount 1. This is a separate issue and will
> be sorted out later. Given that only fsdax pages require the
> notifiacation when the refcount hits 1 now, the PAGEMAP_OPS Kconfig
> symbol can go away and be replaced with a FS_DAX check for this hook
> in the put_page fastpath.
>
> Based on an earlier patch from Ralph Campbell <rcampbell@nvidia.com>.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> arch/powerpc/kvm/book3s_hv_uvmem.c | 1 -
> drivers/gpu/drm/amd/amdkfd/kfd_migrate.c | 1 -
> drivers/gpu/drm/nouveau/nouveau_dmem.c | 1 -
> fs/Kconfig | 1 -
> include/linux/memremap.h | 12 +++--
> include/linux/mm.h | 6 +--
> lib/test_hmm.c | 1 -
> mm/Kconfig | 4 --
> mm/internal.h | 2 +
> mm/memcontrol.c | 11 ++---
> mm/memremap.c | 57 ++++++++----------------
> mm/migrate.c | 6 ---
> mm/swap.c | 16 ++-----
> 13 files changed, 36 insertions(+), 83 deletions(-)
It looks like a good next step to me
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> struct dev_pagemap_ops {
> /*
> - * Called once the page refcount reaches 1. (ZONE_DEVICE pages never
> - * reach 0 refcount unless there is a refcount bug. This allows the
> - * device driver to implement its own memory management.)
> + * Called once the page refcount reaches 0. The reference count will be
> + * reset to one by the core code after the method is called to prepare
> + * for handing out the page again.
I did prefer Ralph's version of this that kept the refcount at 0 while
the page was on the free-list. I hope we can get there again after
later series :)
Jason
next prev parent reply other threads:[~2022-02-07 19:21 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-07 6:32 start sorting out the ZONE_DEVICE refcount mess Christoph Hellwig
2022-02-07 6:32 ` [PATCH 1/8] mm: remove a pointless CONFIG_ZONE_DEVICE check in memremap_pages Christoph Hellwig
2022-02-07 18:08 ` Dan Williams
2022-02-07 19:22 ` Jason Gunthorpe
2022-02-08 7:17 ` Chaitanya Kulkarni
2022-02-08 8:06 ` Muchun Song
2022-02-07 6:32 ` [PATCH 2/8] mm: remove the __KERNEL__ guard from <linux/mm.h> Christoph Hellwig
2022-02-07 18:08 ` Dan Williams
2022-02-07 19:26 ` Jason Gunthorpe
2022-02-08 7:21 ` Chaitanya Kulkarni
2022-02-08 8:07 ` Muchun Song
2022-02-07 6:32 ` [PATCH 3/8] mm: remove pointless includes from <linux/hmm.h> Christoph Hellwig
2022-02-07 14:01 ` Jason Gunthorpe
2022-02-08 7:27 ` Chaitanya Kulkarni
2022-02-07 6:32 ` [PATCH 4/8] mm: move free_devmap_managed_page to memremap.c Christoph Hellwig
2022-02-07 19:06 ` Dan Williams
2022-02-07 19:27 ` Jason Gunthorpe
2022-02-08 7:34 ` Chaitanya Kulkarni
2022-02-08 8:09 ` Muchun Song
2022-02-07 6:32 ` [PATCH 5/8] mm: simplify freeing of devmap managed pages Christoph Hellwig
2022-02-07 19:34 ` Jason Gunthorpe
2022-02-07 23:42 ` Dan Williams
2022-02-08 7:50 ` Chaitanya Kulkarni
2022-02-07 6:32 ` [PATCH 6/8] mm: don't include <linux/memremap.h> in <linux/mm.h> Christoph Hellwig
2022-02-07 17:38 ` Logan Gunthorpe
2022-02-07 19:35 ` Jason Gunthorpe
2022-02-07 21:19 ` Felix Kuehling
2022-02-08 6:46 ` Christoph Hellwig
2022-02-09 17:48 ` Christoph Hellwig
2022-02-10 2:10 ` Alistair Popple
2022-02-10 6:45 ` Christoph Hellwig
2022-02-10 21:00 ` Felix Kuehling
2022-02-07 23:49 ` Dan Williams
2022-02-08 23:53 ` Dan Williams
2022-02-09 6:22 ` Christoph Hellwig
2022-02-07 6:32 ` [PATCH 7/8] mm: remove the extra ZONE_DEVICE struct page refcount Christoph Hellwig
2022-02-07 19:21 ` Jason Gunthorpe [this message]
2022-02-08 2:25 ` Ralph Campbell
2022-02-09 3:30 ` Dan Williams
2022-02-09 6:23 ` Christoph Hellwig
2022-02-09 12:29 ` Jason Gunthorpe
2022-02-09 13:53 ` Christoph Hellwig
2022-02-09 14:14 ` Jason Gunthorpe
2022-02-07 6:32 ` [PATCH 8/8] fsdax: depend on ZONE_DEVICE || FS_DAX_LIMITED Christoph Hellwig
2022-02-07 19:36 ` Jason Gunthorpe
2022-02-07 23:51 ` start sorting out the ZONE_DEVICE refcount mess Logan Gunthorpe
2022-02-08 3:03 ` Miaohe Lin
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