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Diffstat (limited to 'Documentation/filesystems/vfs.rst')
| -rw-r--r-- | Documentation/filesystems/vfs.rst | 39 |
1 files changed, 9 insertions, 30 deletions
diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst index ae79c30b6c0c..bf051c7da6b8 100644 --- a/Documentation/filesystems/vfs.rst +++ b/Documentation/filesystems/vfs.rst @@ -716,9 +716,8 @@ page lookup by address, and keeping track of pages tagged as Dirty or Writeback. The first can be used independently to the others. The VM can try to -either write dirty pages in order to clean them, or release clean pages -in order to reuse them. To do this it can call the ->writepage method -on dirty pages, and ->release_folio on clean folios with the private +release clean pages in order to reuse them. To do this it can call +->release_folio on clean folios with the private flag set. Clean pages without PagePrivate and with no external references will be released without notice being given to the address_space. @@ -731,8 +730,8 @@ maintains information about the PG_Dirty and PG_Writeback status of each page, so that pages with either of these flags can be found quickly. The Dirty tag is primarily used by mpage_writepages - the default -->writepages method. It uses the tag to find dirty pages to call -->writepage on. If mpage_writepages is not used (i.e. the address +->writepages method. It uses the tag to find dirty pages to +write back. If mpage_writepages is not used (i.e. the address provides its own ->writepages) , the PAGECACHE_TAG_DIRTY tag is almost unused. write_inode_now and sync_inode do use it (through __sync_single_inode) to check if ->writepages has been successful in @@ -756,23 +755,23 @@ pages, however the address_space has finer control of write sizes. The read process essentially only requires 'read_folio'. The write process is more complicated and uses write_begin/write_end or -dirty_folio to write data into the address_space, and writepage and +dirty_folio to write data into the address_space, and writepages to writeback data to storage. Adding and removing pages to/from an address_space is protected by the inode's i_mutex. When data is written to a page, the PG_Dirty flag should be set. It -typically remains set until writepage asks for it to be written. This +typically remains set until writepages asks for it to be written. This should clear PG_Dirty and set PG_Writeback. It can be actually written at any point after PG_Dirty is clear. Once it is known to be safe, PG_Writeback is cleared. Writeback makes use of a writeback_control structure to direct the -operations. This gives the writepage and writepages operations some +operations. This gives the writepages operation some information about the nature of and reason for the writeback request, and the constraints under which it is being done. It is also used to -return information back to the caller about the result of a writepage or +return information back to the caller about the result of a writepages request. @@ -819,7 +818,6 @@ cache in your filesystem. The following members are defined: .. code-block:: c struct address_space_operations { - int (*writepage)(struct page *page, struct writeback_control *wbc); int (*read_folio)(struct file *, struct folio *); int (*writepages)(struct address_space *, struct writeback_control *); bool (*dirty_folio)(struct address_space *, struct folio *); @@ -848,25 +846,6 @@ cache in your filesystem. The following members are defined: int (*swap_rw)(struct kiocb *iocb, struct iov_iter *iter); }; -``writepage`` - called by the VM to write a dirty page to backing store. This - may happen for data integrity reasons (i.e. 'sync'), or to free - up memory (flush). The difference can be seen in - wbc->sync_mode. The PG_Dirty flag has been cleared and - PageLocked is true. writepage should start writeout, should set - PG_Writeback, and should make sure the page is unlocked, either - synchronously or asynchronously when the write operation - completes. - - If wbc->sync_mode is WB_SYNC_NONE, ->writepage doesn't have to - try too hard if there are problems, and may choose to write out - other pages from the mapping if that is easier (e.g. due to - internal dependencies). If it chooses not to start writeout, it - should return AOP_WRITEPAGE_ACTIVATE so that the VM will not - keep calling ->writepage on that page. - - See the file "Locking" for more details. - ``read_folio`` Called by the page cache to read a folio from the backing store. The 'file' argument supplies authentication information to network @@ -909,7 +888,7 @@ cache in your filesystem. The following members are defined: given and that many pages should be written if possible. If no ->writepages is given, then mpage_writepages is used instead. This will choose pages from the address space that are tagged as - DIRTY and will pass them to ->writepage. + DIRTY and will write them back. ``dirty_folio`` called by the VM to mark a folio as dirty. This is particularly |