From: Jan Kara <jack@suse.cz>
To: John Hubbard <jhubbard@nvidia.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Al Viro" <viro@zeniv.linux.org.uk>,
"Alex Williamson" <alex.williamson@redhat.com>,
"Benjamin Herrenschmidt" <benh@kernel.crashing.org>,
"Björn Töpel" <bjorn.topel@intel.com>,
"Christoph Hellwig" <hch@infradead.org>,
"Dan Williams" <dan.j.williams@intel.com>,
"Daniel Vetter" <daniel@ffwll.ch>,
"Dave Chinner" <david@fromorbit.com>,
"David Airlie" <airlied@linux.ie>,
"David S . Miller" <davem@davemloft.net>,
"Ira Weiny" <ira.weiny@intel.com>, "Jan Kara" <jack@suse.cz>,
"Jason Gunthorpe" <jgg@ziepe.ca>, "Jens Axboe" <axboe@kernel.dk>,
"Jonathan Corbet" <corbet@lwn.net>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Magnus Karlsson" <magnus.karlsson@intel.com>,
"Mauro Carvalho Chehab" <mchehab@kernel.org>,
"Michael Ellerman" <mpe@ellerman.id.au>,
"Michal Hocko" <mhocko@suse.com>,
"Mike Kravetz" <mike.kravetz@oracle.com>,
"Paul Mackerras" <paulus@samba.org>,
"Shuah Khan" <shuah@kernel.org>,
"Vlastimil Babka" <vbabka@suse.cz>,
bpf@vger.kernel.org, dri-devel@lists.freedesktop.org,
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LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 04/23] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages
Date: Wed, 13 Nov 2019 11:49:20 +0100 [thread overview]
Message-ID: <20191113104920.GF6367@quack2.suse.cz> (raw)
In-Reply-To: <20191113042710.3997854-5-jhubbard@nvidia.com>
On Tue 12-11-19 20:26:51, John Hubbard wrote:
> An upcoming patch changes and complicates the refcounting and
> especially the "put page" aspects of it. In order to keep
> everything clean, refactor the devmap page release routines:
>
> * Rename put_devmap_managed_page() to page_is_devmap_managed(),
> and limit the functionality to "read only": return a bool,
> with no side effects.
>
> * Add a new routine, put_devmap_managed_page(), to handle checking
> what kind of page it is, and what kind of refcount handling it
> requires.
>
> * Rename __put_devmap_managed_page() to free_devmap_managed_page(),
> and limit the functionality to unconditionally freeing a devmap
> page.
>
> This is originally based on a separate patch by Ira Weiny, which
> applied to an early version of the put_user_page() experiments.
> Since then, Jérôme Glisse suggested the refactoring described above.
>
> Suggested-by: Jérôme Glisse <jglisse@redhat.com>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Looks good to me. You can add:
Reviewed-by: Jan Kara <jack@suse.cz>
Honza
> ---
> include/linux/mm.h | 27 ++++++++++++++++---
> mm/memremap.c | 67 ++++++++++++++++++++--------------------------
> 2 files changed, 53 insertions(+), 41 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index a2adf95b3f9c..96228376139c 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -967,9 +967,10 @@ static inline bool is_zone_device_page(const struct page *page)
> #endif
>
> #ifdef CONFIG_DEV_PAGEMAP_OPS
> -void __put_devmap_managed_page(struct page *page);
> +void free_devmap_managed_page(struct page *page);
> DECLARE_STATIC_KEY_FALSE(devmap_managed_key);
> -static inline bool put_devmap_managed_page(struct page *page)
> +
> +static inline bool page_is_devmap_managed(struct page *page)
> {
> if (!static_branch_unlikely(&devmap_managed_key))
> return false;
> @@ -978,7 +979,6 @@ static inline bool put_devmap_managed_page(struct page *page)
> switch (page->pgmap->type) {
> case MEMORY_DEVICE_PRIVATE:
> case MEMORY_DEVICE_FS_DAX:
> - __put_devmap_managed_page(page);
> return true;
> default:
> break;
> @@ -986,6 +986,27 @@ static inline bool put_devmap_managed_page(struct page *page)
> return false;
> }
>
> +static inline bool put_devmap_managed_page(struct page *page)
> +{
> + bool is_devmap = page_is_devmap_managed(page);
> +
> + if (is_devmap) {
> + int count = page_ref_dec_return(page);
> +
> + /*
> + * devmap page refcounts are 1-based, rather than 0-based: if
> + * refcount is 1, then the page is free and the refcount is
> + * stable because nobody holds a reference on the page.
> + */
> + if (count == 1)
> + free_devmap_managed_page(page);
> + else if (!count)
> + __put_page(page);
> + }
> +
> + return is_devmap;
> +}
> +
> #else /* CONFIG_DEV_PAGEMAP_OPS */
> static inline bool put_devmap_managed_page(struct page *page)
> {
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 03ccbdfeb697..bc7e2a27d025 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -410,48 +410,39 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
> EXPORT_SYMBOL_GPL(get_dev_pagemap);
>
> #ifdef CONFIG_DEV_PAGEMAP_OPS
> -void __put_devmap_managed_page(struct page *page)
> +void free_devmap_managed_page(struct page *page)
> {
> - int count = page_ref_dec_return(page);
> + /* Clear Active bit in case of parallel mark_page_accessed */
> + __ClearPageActive(page);
> + __ClearPageWaiters(page);
> +
> + mem_cgroup_uncharge(page);
>
> /*
> - * If refcount is 1 then page is freed and refcount is stable as nobody
> - * holds a reference on the page.
> + * When a device_private page is freed, the page->mapping field
> + * may still contain a (stale) mapping value. For example, the
> + * lower bits of page->mapping may still identify the page as
> + * an anonymous page. Ultimately, this entire field is just
> + * stale and wrong, and it will cause errors if not cleared.
> + * One example is:
> + *
> + * migrate_vma_pages()
> + * migrate_vma_insert_page()
> + * page_add_new_anon_rmap()
> + * __page_set_anon_rmap()
> + * ...checks page->mapping, via PageAnon(page) call,
> + * and incorrectly concludes that the page is an
> + * anonymous page. Therefore, it incorrectly,
> + * silently fails to set up the new anon rmap.
> + *
> + * For other types of ZONE_DEVICE pages, migration is either
> + * handled differently or not done at all, so there is no need
> + * to clear page->mapping.
> */
> - if (count == 1) {
> - /* Clear Active bit in case of parallel mark_page_accessed */
> - __ClearPageActive(page);
> - __ClearPageWaiters(page);
> -
> - mem_cgroup_uncharge(page);
> -
> - /*
> - * When a device_private page is freed, the page->mapping field
> - * may still contain a (stale) mapping value. For example, the
> - * lower bits of page->mapping may still identify the page as
> - * an anonymous page. Ultimately, this entire field is just
> - * stale and wrong, and it will cause errors if not cleared.
> - * One example is:
> - *
> - * migrate_vma_pages()
> - * migrate_vma_insert_page()
> - * page_add_new_anon_rmap()
> - * __page_set_anon_rmap()
> - * ...checks page->mapping, via PageAnon(page) call,
> - * and incorrectly concludes that the page is an
> - * anonymous page. Therefore, it incorrectly,
> - * silently fails to set up the new anon rmap.
> - *
> - * For other types of ZONE_DEVICE pages, migration is either
> - * handled differently or not done at all, so there is no need
> - * to clear page->mapping.
> - */
> - if (is_device_private_page(page))
> - page->mapping = NULL;
> + if (is_device_private_page(page))
> + page->mapping = NULL;
>
> - page->pgmap->ops->page_free(page);
> - } else if (!count)
> - __put_page(page);
> + page->pgmap->ops->page_free(page);
> }
> -EXPORT_SYMBOL(__put_devmap_managed_page);
> +EXPORT_SYMBOL(free_devmap_managed_page);
> #endif /* CONFIG_DEV_PAGEMAP_OPS */
> --
> 2.24.0
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2019-11-13 10:49 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-13 4:26 [PATCH v4 00/23] mm/gup: track dma-pinned pages: FOLL_PIN, FOLL_LONGTERM John Hubbard
2019-11-13 4:26 ` [PATCH v4 01/23] mm/gup: pass flags arg to __gup_device_* functions John Hubbard
2019-11-13 10:50 ` Jan Kara
2019-11-13 4:26 ` [PATCH v4 02/23] mm/gup: factor out duplicate code from four routines John Hubbard
2019-11-13 11:15 ` Jan Kara
2019-11-13 23:12 ` John Hubbard
2019-11-13 4:26 ` [PATCH v4 03/23] mm/gup: move try_get_compound_head() to top, fix minor issues John Hubbard
2019-11-13 10:50 ` Jan Kara
2019-11-13 18:38 ` Ira Weiny
2019-11-13 4:26 ` [PATCH v4 04/23] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages John Hubbard
2019-11-13 10:49 ` Jan Kara [this message]
2019-11-13 19:09 ` Jerome Glisse
2019-11-13 19:23 ` Dan Williams
2019-11-13 22:00 ` Dan Williams
2019-11-13 22:46 ` John Hubbard
2019-11-13 22:55 ` Dan Williams
2019-11-13 22:56 ` John Hubbard
2019-11-13 23:03 ` Jerome Glisse
2019-11-13 4:26 ` [PATCH v4 05/23] goldish_pipe: rename local pin_user_pages() routine John Hubbard
2019-11-13 4:26 ` [PATCH v4 06/23] IB/umem: use get_user_pages_fast() to pin DMA pages John Hubbard
2019-11-13 4:26 ` [PATCH v4 07/23] media/v4l2-core: set pages dirty upon releasing DMA buffers John Hubbard
2019-11-13 4:26 ` [PATCH v4 08/23] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM John Hubbard
2019-11-13 13:02 ` Jason Gunthorpe
2019-11-13 19:17 ` Ira Weiny
2019-11-13 20:19 ` John Hubbard
2019-11-13 18:47 ` Ira Weiny
2019-11-13 4:26 ` [PATCH v4 09/23] mm/gup: introduce pin_user_pages*() and FOLL_PIN John Hubbard
2019-11-13 10:43 ` Jan Kara
2019-11-13 18:31 ` Ira Weiny
2019-11-13 18:45 ` Dan Williams
2019-11-13 23:22 ` John Hubbard
2019-11-14 6:08 ` John Hubbard
2019-11-13 18:59 ` Ira Weiny
2019-11-13 20:24 ` John Hubbard
2019-11-13 4:26 ` [PATCH v4 10/23] goldish_pipe: convert to pin_user_pages() and put_user_page() John Hubbard
2019-11-13 4:26 ` [PATCH v4 11/23] IB/{core,hw,umem}: set FOLL_PIN, FOLL_LONGTERM via pin_longterm_pages*() John Hubbard
2019-11-13 4:26 ` [PATCH v4 12/23] mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote() John Hubbard
2019-11-13 4:27 ` [PATCH v4 13/23] drm/via: set FOLL_PIN via pin_user_pages_fast() John Hubbard
2019-11-13 4:27 ` [PATCH v4 14/23] fs/io_uring: set FOLL_PIN via pin_user_pages() John Hubbard
2019-11-13 4:27 ` [PATCH v4 15/23] net/xdp: " John Hubbard
2019-11-13 4:27 ` [PATCH v4 16/23] mm/gup: track FOLL_PIN pages John Hubbard
2019-11-13 4:27 ` [PATCH v4 17/23] media/v4l2-core: pin_longterm_pages (FOLL_PIN) and put_user_page() conversion John Hubbard
2019-11-13 4:27 ` [PATCH v4 18/23] vfio, mm: " John Hubbard
2019-11-13 4:27 ` [PATCH v4 19/23] powerpc: book3s64: convert to pin_longterm_pages() and put_user_page() John Hubbard
2019-11-13 4:27 ` [PATCH v4 20/23] mm/gup_benchmark: use proper FOLL_WRITE flags instead of hard-coding "1" John Hubbard
2019-11-13 19:01 ` Ira Weiny
2019-11-13 4:27 ` [PATCH v4 21/23] mm/gup_benchmark: support pin_user_pages() and related calls John Hubbard
2019-11-13 19:03 ` Ira Weiny
2019-11-13 4:27 ` [PATCH v4 22/23] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage John Hubbard
2019-11-13 19:06 ` Ira Weiny
2019-11-13 4:27 ` [PATCH v4 23/23] mm/gup: remove support for gup(FOLL_LONGTERM) John Hubbard
2019-11-13 19:09 ` Ira Weiny
2019-11-13 23:27 ` John Hubbard
2019-11-13 4:32 ` [PATCH v4 00/23] mm/gup: track dma-pinned pages: FOLL_PIN, FOLL_LONGTERM John Hubbard
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