Re: [PATCH v1 01/14] ext4/xfs: add page refcount helper

Darrick J. Wong
2021-08-25T15:49:25Z

On Tue, Aug 24, 2021 at 10:48:15PM -0500, Alex Sierra wrote:
> 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>
> Signed-off-by: Alex Sierra <alex.sierra@amd.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>

Looks fine to me,
Acked-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
> v3:
> [AS]: rename dax_layout_is_idle_page func to dax_page_unused
>
> v4:
> [AS]: This ref count functionality was missing on fuse/dax.c.
> ---
> fs/dax.c | 4 ++--
> fs/ext4/inode.c | 5 +----
> fs/fuse/dax.c | 4 +---
> fs/xfs/xfs_file.c | 4 +---
> include/linux/dax.h | 10 ++++++++++
> 5 files changed, 15 insertions(+), 12 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 62352cbcf0f4..c387d09e3e5a 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -369,7 +369,7 @@ 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_page_unused(page));
> WARN_ON_ONCE(page->mapping && page->mapping != mapping);
> page->mapping = NULL;
> page->index = 0;
> @@ -383,7 +383,7 @@ 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_page_unused(page))
> return page;
> }
> return NULL;
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index fe6045a46599..05ffe6875cb1 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3971,10 +3971,7 @@ 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/fuse/dax.c b/fs/fuse/dax.c
> index ff99ab2a3c43..2b1f190ba78a 100644
> --- a/fs/fuse/dax.c
> +++ b/fs/fuse/dax.c
> @@ -677,9 +677,7 @@ static int __fuse_dax_break_layouts(struct inode *inode, bool *retry,
> return 0;
>
> *retry = true;
> - return ___wait_var_event(&page->_refcount,
> - atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE,
> - 0, 0, fuse_wait_dax_page(inode));
> + return dax_wait_page(inode, page, fuse_wait_dax_page);
> }
>
> /* dmap_end == 0 leads to unmapping of whole file */
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 396ef36dcd0a..182057281086 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -840,9 +840,7 @@ 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..8b5da1d60dbc 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_page_unused(struct page *page)
> +{
> + return page_ref_count(page) == 1;
> +}
> +
> +#define dax_wait_page(_inode, _page, _wait_cb) \
> + ___wait_var_event(&(_page)->_refcount, \
> + dax_page_unused(_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
> --
> 2.32.0
>