| Message ID | 20220127124058.1172422-6-ruansy.fnst@fujitsu.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | fsdax: introduce fs query to support reflink | expand |
On Thu, Jan 27, 2022 at 4:41 AM Shiyang Ruan <ruansy.fnst@fujitsu.com> 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 I do not see a call to dax_lock_entry() in this function, what keeps this lookup valid after xas_unlock_irq()?
在 2022/2/16 9:34, Dan Williams 写道: > On Thu, Jan 27, 2022 at 4:41 AM Shiyang Ruan <ruansy.fnst@fujitsu.com> 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 > > I do not see a call to dax_lock_entry() in this function, what keeps > this lookup valid after xas_unlock_irq()? I am not sure if I understood your advice correctly: You said dax_lock_entry() is not necessary in v9[1]. So, I deleted it. [1]: https://lore.kernel.org/linux-xfs/CAPcyv4jVDfpHb1DCW+NLXH2YBgLghCVy8o6wrc02CXx4g-Bv7Q@mail.gmail.com/ -- Thanks, Ruan.
On Tue, Feb 15, 2022 at 7:02 PM Shiyang Ruan <ruansy.fnst@fujitsu.com> wrote: > > > > 在 2022/2/16 9:34, Dan Williams 写道: > > On Thu, Jan 27, 2022 at 4:41 AM Shiyang Ruan <ruansy.fnst@fujitsu.com> 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 > > > > I do not see a call to dax_lock_entry() in this function, what keeps > > this lookup valid after xas_unlock_irq()? > > I am not sure if I understood your advice correctly: You said > dax_lock_entry() is not necessary in v9[1]. So, I deleted it. > > [1]: > https://lore.kernel.org/linux-xfs/CAPcyv4jVDfpHb1DCW+NLXH2YBgLghCVy8o6wrc02CXx4g-Bv7Q@mail.gmail.com/ I also said, "if the filesystem can make those guarantees" it was not clear whether this helper is being called back from an FS context that guarantees those associations or not. As far as I can see there is nothing that protects that association. Apologies for the confusion, I was misunderstanding where the protection was being enforced in this case.
diff --git a/fs/dax.c b/fs/dax.c index c8d57080c1aa..964512107c23 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -455,6 +455,50 @@ void dax_unlock_page(struct page *page, dax_entry_t cookie) dax_unlock_entry(&xas, (void *)cookie); } +/* + * dax_load_page - Load the page corresponding to a (mapping,offset) + * @mapping: the file's mapping whose entry we want to load + * @index: the offset within this file + * @page: output the dax page corresponding to this dax entry + * + * Return: error if it isn't a dax mapping, otherwise 0. + */ +int dax_load_page(struct address_space *mapping, pgoff_t index, + struct page **page) +{ + XA_STATE(xas, &mapping->i_pages, 0); + void *entry; + + if (!dax_mapping(mapping)) + return -EBUSY; + + rcu_read_lock(); + for (;;) { + entry = NULL; + 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)) { + /* + * Output the page if the dax entry exists and isn't + * a zero or empty entry. + */ + *page = pfn_to_page(dax_to_pfn(entry)); + } + xas_unlock_irq(&xas); + break; + } + rcu_read_unlock(); + return 0; +} + /* * 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 96cfc63b12fd..530ff9733dd9 100644 --- a/include/linux/dax.h +++ b/include/linux/dax.h @@ -155,6 +155,8 @@ 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); +int dax_load_page(struct address_space *mapping, + unsigned long index, struct page **page); #else static inline struct page *dax_layout_busy_page(struct address_space *mapping) { @@ -182,6 +184,12 @@ 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 int dax_load_page(struct address_space *mapping, + unsigned long index, struct page **page) +{ + return 0; +} #endif int dax_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero,