On Tue, Oct 06, 2020 at 04:09:30PM -0700, Ralph Campbell wrote:
> 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 <rcampb...@nvidia.com>
> Reviewed-by: Christoph Hellwig <h...@lst.de>
> ---
>
> I'm resending this as a separate patch since I think it is ready to
> merge. Originally, this was part of an RFC and is unchanged from v3:
> https://lore.kernel.org/linux-mm/20201001181715.17416-1-rcampb...@nvidia.com
>
> It applies cleanly to linux-5.9.0-rc7-mm1 but doesn't really
> depend on anything, just simple merge conflicts when applied to
> other trees.
> I'll let the various maintainers decide which tree and when to merge.
> It isn't urgent since it is a clean up patch.
>
> 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 5b47834f2e1b..85c63f735909 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 771ed8b1fadb..132620cbfa13 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3937,10 +3937,7 @@ 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 3d1b95124744..a5304aaeaa3a 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -749,9 +749,7 @@ 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);
I don't mind this open-coded soup getting cleaned up into a macro,
though my general opinion is that if the mm/dax developers are ok with
this then:
Acked-by: Darrick J. Wong <darrick.w...@oracle.com>
--D
> }
>
> 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;
> +}
> +
> +#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
> --
> 2.20.1
>
