On Fri, Sep 24, 2021 at 09:09:56PM +0800, Shiyang Ruan wrote:
> The current dax_lock_page() locks dax entry by obtaining mapping and
> index in page. To support 1-to-N RMAP in NVDIMM, we need a new function
> to lock a specific dax entry corresponding to this file's mapping,index.
> And BTW, output the page corresponding to the specific dax entry for
> caller use.
>
> Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
> ---
> fs/dax.c | 65 ++++++++++++++++++++++++++++++++++++++++++++-
> include/linux/dax.h | 15 +++++++++++
> 2 files changed, 79 insertions(+), 1 deletion(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 798c43f09eee..509b65e60478 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -390,7 +390,7 @@ static struct page *dax_busy_page(void *entry)
> }
>
> /*
> - * dax_lock_mapping_entry - Lock the DAX entry corresponding to a page
> + * dax_lock_page - Lock the DAX entry corresponding to a page
> * @page: The page whose entry we want to lock
> *
> * Context: Process context.
> @@ -455,6 +455,69 @@ void dax_unlock_page(struct page *page, dax_entry_t cookie)
> dax_unlock_entry(&xas, (void *)cookie);
> }
>
> +/*
> + * dax_lock_mapping_entry - Lock the DAX entry corresponding to a mapping
> + * @mapping: the file's mapping whose entry we want to lock
> + * @index: the offset within this file
> + * @page: output the dax page corresponding to this dax entry
> + *
> + * Return: A cookie to pass to dax_unlock_mapping_entry() or 0 if the entry
> + * could not be locked.
> + */
> +dax_entry_t dax_lock_mapping_entry(struct address_space *mapping, pgoff_t index,
> + struct page **page)
> +{
> + XA_STATE(xas, NULL, 0);
> + void *entry;
> +
> + rcu_read_lock();
> + for (;;) {
> + entry = NULL;
> + if (!dax_mapping(mapping))
> + break;
> +
> + xas.xa = &mapping->i_pages;
> + xas_lock_irq(&xas);
> + xas_set(&xas, index);
> + entry = xas_load(&xas);
> + if (dax_is_locked(entry)) {
> + rcu_read_unlock();
> + wait_entry_unlocked(&xas, entry);
> + rcu_read_lock();
> + continue;
> + }
> + if (!entry ||
> + dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
> + /*
> + * Because we are looking for entry from file's mapping
> + * and index, so the entry may not be inserted for now,
> + * or even a zero/empty entry. We don't think this is
> + * an error case. So, return a special value and do
> + * not output @page.
> + */
> + entry = (void *)~0UL;
I kinda wonder if these open-coded magic values ~0UL (no entry) and 0
(cannot lock) should be #defines that force-cast the magic value to
dax_entry_t...
...but then I'm not really an expert in the design behind fs/dax.c --
this part looks reasonable enough to me, but I think Dan or Matthew
ought to look this over.
--D
> + } else {
> + *page = pfn_to_page(dax_to_pfn(entry));
> + dax_lock_entry(&xas, entry);
> + }
> + xas_unlock_irq(&xas);
> + break;
> + }
> + rcu_read_unlock();
> + return (dax_entry_t)entry;
> +}
> +
> +void dax_unlock_mapping_entry(struct address_space *mapping, pgoff_t index,
> + dax_entry_t cookie)
> +{
> + XA_STATE(xas, &mapping->i_pages, index);
> +
> + if (cookie == ~0UL)
> + return;
> +
> + dax_unlock_entry(&xas, (void *)cookie);
> +}
> +
> /*
> * Find page cache entry at given index. If it is a DAX entry, return it
> * with the entry locked. If the page cache doesn't contain an entry at
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index d273d59723cd..65411bee4312 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -156,6 +156,10 @@ struct page *dax_layout_busy_page(struct address_space *mapping);
> struct page *dax_layout_busy_page_range(struct address_space *mapping, loff_t start, loff_t end);
> dax_entry_t dax_lock_page(struct page *page);
> void dax_unlock_page(struct page *page, dax_entry_t cookie);
> +dax_entry_t dax_lock_mapping_entry(struct address_space *mapping,
> + unsigned long index, struct page **page);
> +void dax_unlock_mapping_entry(struct address_space *mapping,
> + unsigned long index, dax_entry_t cookie);
> #else
> #define generic_fsdax_supported NULL
>
> @@ -201,6 +205,17 @@ static inline dax_entry_t dax_lock_page(struct page *page)
> static inline void dax_unlock_page(struct page *page, dax_entry_t cookie)
> {
> }
> +
> +static inline dax_entry_t dax_lock_mapping_entry(struct address_space *mapping,
> + unsigned long index, struct page **page)
> +{
> + return 0;
> +}
> +
> +static inline void dax_unlock_mapping_entry(struct address_space *mapping,
> + unsigned long index, dax_entry_t cookie)
> +{
> +}
> #endif
>
> #if IS_ENABLED(CONFIG_DAX)
> --
> 2.33.0
>
>
>
