From: Liam Howlett <liam.howlett@oracle.com>
To: Alex Sierra <alex.sierra@amd.com>
Cc: "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"Felix.Kuehling@amd.com" <Felix.Kuehling@amd.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"rcampbell@nvidia.com" <rcampbell@nvidia.com>,
"amd-gfx@lists.freedesktop.org" <amd-gfx@lists.freedesktop.org>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>, "hch@lst.de" <hch@lst.de>,
"jgg@nvidia.com" <jgg@nvidia.com>,
"jglisse@redhat.com" <jglisse@redhat.com>
Subject: Re: [RFC PATCH v2 1/8] ext4/xfs: add page refcount helper
Date: Tue, 8 Jun 2021 00:29:04 +0000 [thread overview]
Message-ID: <20210608002858.gegg6sl2z2dwwstb@revolver> (raw)
In-Reply-To: <20210607204226.7743-2-alex.sierra@amd.com>
* Alex Sierra <alex.sierra@amd.com> [210607 16:43]:
> From: Ralph Campbell <rcampbell@nvidia.com>
>
> There are several places where ZONE_DEVICE struct pages assume a reference
> count == 1 means the page is idle and free. Instead of open coding this,
> add a helper function to hide this detail.
>
> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
> ---
> fs/dax.c | 4 ++--
> fs/ext4/inode.c | 5 +----
> fs/xfs/xfs_file.c | 4 +---
> include/linux/dax.h | 10 ++++++++++
> 4 files changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 26d5dcd2d69e..321f4ddc6643 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -358,7 +358,7 @@ static void dax_disassociate_entry(void *entry, struct address_space *mapping,
> for_each_mapped_pfn(entry, pfn) {
> struct page *page = pfn_to_page(pfn);
>
> - WARN_ON_ONCE(trunc && page_ref_count(page) > 1);
> + WARN_ON_ONCE(trunc && !dax_layout_is_idle_page(page));
> WARN_ON_ONCE(page->mapping && page->mapping != mapping);
> page->mapping = NULL;
> page->index = 0;
> @@ -372,7 +372,7 @@ static struct page *dax_busy_page(void *entry)
> for_each_mapped_pfn(entry, pfn) {
> struct page *page = pfn_to_page(pfn);
>
> - if (page_ref_count(page) > 1)
> + if (!dax_layout_is_idle_page(page))
> return page;
> }
> return NULL;
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index c173c8405856..9ee00186412f 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3972,10 +3972,7 @@ int ext4_break_layouts(struct inode *inode)
> if (!page)
> return 0;
>
> - error = ___wait_var_event(&page->_refcount,
> - atomic_read(&page->_refcount) == 1,
> - TASK_INTERRUPTIBLE, 0, 0,
> - ext4_wait_dax_page(ei));
> + error = dax_wait_page(ei, page, ext4_wait_dax_page);
> } while (error == 0);
>
> return error;
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 5b0f93f73837..39565fe5f817 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -782,9 +782,7 @@ xfs_break_dax_layouts(
> return 0;
>
> *retry = true;
> - return ___wait_var_event(&page->_refcount,
> - atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE,
> - 0, 0, xfs_wait_dax_page(inode));
> + return dax_wait_page(inode, page, xfs_wait_dax_page);
> }
>
> int
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index b52f084aa643..8909a91cd381 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -243,6 +243,16 @@ static inline bool dax_mapping(struct address_space *mapping)
> return mapping->host && IS_DAX(mapping->host);
> }
>
> +static inline bool dax_layout_is_idle_page(struct page *page)
> +{
> + return page_ref_count(page) == 1;
> +}
If this races with page_ref_count(page) == 0, then it will return false
that a page is idle when the page is being freed. I don't know the code
well enough to say if this is an issue or not so please let me know.
For example:
!dax_layout_is_idle_page() will return true in dax_busy_page() above
when the count is 0 and return the page.
Maybe you are sure to have at least one reference when calling this? It
might be worth adding a comment.
> +
> +#define dax_wait_page(_inode, _page, _wait_cb) \
> + ___wait_var_event(&(_page)->_refcount, \
> + dax_layout_is_idle_page(_page), \
> + TASK_INTERRUPTIBLE, 0, 0, _wait_cb(_inode))
> +
> #ifdef CONFIG_DEV_DAX_HMEM_DEVICES
> void hmem_register_device(int target_nid, struct resource *r);
> #else
> --
> 2.17.1
>
>
next prev parent reply other threads:[~2021-06-08 0:29 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-07 20:42 [RFC PATCH v2 0/8] Support DEVICE_GENERIC memory in migrate_vma_* Alex Sierra
2021-06-07 20:42 ` [RFC PATCH v2 1/8] ext4/xfs: add page refcount helper Alex Sierra
2021-06-08 0:29 ` Liam Howlett [this message]
2021-06-08 14:33 ` Matthew Wilcox
2021-06-09 19:23 ` Matthew Wilcox
2021-06-14 15:26 ` Felix Kuehling
2021-06-07 20:42 ` [RFC PATCH v2 2/8] mm: remove extra ZONE_DEVICE struct page refcount Alex Sierra
2021-06-07 20:42 ` [RFC PATCH v2 3/8] kernel: resource: lookup_resource as exported symbol Alex Sierra
2021-06-07 20:42 ` [RFC PATCH v2 4/8] drm/amdkfd: add SPM support for SVM Alex Sierra
2021-06-07 20:42 ` [RFC PATCH v2 5/8] drm/amdkfd: generic type as sys mem on migration to ram Alex Sierra
2021-06-07 20:42 ` [RFC PATCH v2 6/8] include/linux/mm.h: helpers to check zone device generic type Alex Sierra
2021-06-07 20:42 ` [RFC PATCH v2 7/8] mm: add generic type support to migrate_vma helpers Alex Sierra
2021-06-07 20:42 ` [RFC PATCH v2 8/8] mm: call pgmap->ops->page_free for DEVICE_GENERIC pages Alex Sierra
2021-06-08 14:26 ` [RFC PATCH v2 0/8] Support DEVICE_GENERIC memory in migrate_vma_* Matthew Wilcox
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