netfs: Replace PG_fscache by setting folio->private and marking dirty

When dirty data is being written to the cache, setting/waiting on/clearing
the fscache flag is always done in tandem with setting/waiting on/clearing
the writeback flag.  The netfslib buffered write routines wait on and set
both flags and the write request cleanup clears both flags, so the fscache
flag is almost superfluous.

The reason it isn't superfluous is because the fscache flag is also used to
indicate that data just read from the server is being written to the cache.
The flag is used to prevent a race involving overlapping direct-I/O writes
to the cache.

Change this to indicate that a page is in need of being copied to the cache
by placing a magic value in folio->private and marking the folios dirty.
Then when the writeback code sees a folio marked in this way, it only
writes it to the cache and not to the server.

If a folio that has this magic value set is modified, the value is just
replaced and the folio will then be uplodaded too.

With this, PG_fscache is no longer required by the netfslib core, 9p and
afs.

Ceph and nfs, however, still need to use the old PG_fscache-based tracking.
To deal with this, a flag, NETFS_ICTX_USE_PGPRIV2, now has to be set on the
flags in the netfs_inode struct for those filesystems.  This reenables the
use of PG_fscache in that inode.  9p and afs use the netfslib write helpers
so get switched over; cifs, for the moment, does page-by-page manual access
to the cache, so doesn't use PG_fscache and is unaffected.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: Matthew Wilcox (Oracle) <willy@infradead.org>
cc: Eric Van Hensbergen <ericvh@kernel.org>
cc: Latchesar Ionkov <lucho@ionkov.net>
cc: Dominique Martinet <asmadeus@codewreck.org>
cc: Christian Schoenebeck <linux_oss@crudebyte.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Ilya Dryomov <idryomov@gmail.com>
cc: Xiubo Li <xiubli@redhat.com>
cc: Steve French <sfrench@samba.org>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
cc: Shyam Prasad N <sprasad@microsoft.com>
cc: Tom Talpey <tom@talpey.com>
cc: Bharath SM <bharathsm@microsoft.com>
cc: Trond Myklebust <trond.myklebust@hammerspace.com>
cc: Anna Schumaker <anna@kernel.org>
cc: netfs@lists.linux.dev
cc: v9fs@lists.linux.dev
cc: linux-afs@lists.infradead.org
cc: ceph-devel@vger.kernel.org
cc: linux-cifs@vger.kernel.org
cc: linux-nfs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org

1 files changed, 14 insertions, 8 deletions

diff --git a/include/linux/fscache.h b/include/linux/fscache.h
index 6e8562cbcc43..9de27643607f 100644
--- a/include/linux/fscache.h
+++ b/include/linux/fscache.h
@@ -172,9 +172,12 @@ extern void __fscache_invalidate(struct fscache_cookie *, const void *, loff_t,
 extern int __fscache_begin_read_operation(struct netfs_cache_resources *, struct fscache_cookie *);
 extern int __fscache_begin_write_operation(struct netfs_cache_resources *, struct fscache_cookie *);
 
-extern void __fscache_write_to_cache(struct fscache_cookie *, struct address_space *,
-				     loff_t, size_t, loff_t, netfs_io_terminated_t, void *,
-				     bool);
+void __fscache_write_to_cache(struct fscache_cookie *cookie,
+			      struct address_space *mapping,
+			      loff_t start, size_t len, loff_t i_size,
+			      netfs_io_terminated_t term_func,
+			      void *term_func_priv,
+			      bool using_pgpriv2, bool cond);
 extern void __fscache_clear_page_bits(struct address_space *, loff_t, size_t);
 
 /**
@@ -597,7 +600,8 @@ static inline void fscache_clear_page_bits(struct address_space *mapping,
  * @i_size: The new size of the inode
  * @term_func: The function to call upon completion
  * @term_func_priv: The private data for @term_func
- * @caching: If PG_fscache has been set
+ * @using_pgpriv2: If we're using PG_private_2 to mark in-progress write
+ * @caching: If we actually want to do the caching
  *
  * Helper function for a netfs to write dirty data from an inode into the cache
  * object that's backing it.
@@ -608,19 +612,21 @@ static inline void fscache_clear_page_bits(struct address_space *mapping,
  * marked with PG_fscache.
  *
  * If given, @term_func will be called upon completion and supplied with
- * @term_func_priv.  Note that the PG_fscache flags will have been cleared by
- * this point, so the netfs must retain its own pin on the mapping.
+ * @term_func_priv.  Note that if @using_pgpriv2 is set, the PG_private_2 flags
+ * will have been cleared by this point, so the netfs must retain its own pin
+ * on the mapping.
  */
 static inline void fscache_write_to_cache(struct fscache_cookie *cookie,
 					  struct address_space *mapping,
 					  loff_t start, size_t len, loff_t i_size,
 					  netfs_io_terminated_t term_func,
 					  void *term_func_priv,
-					  bool caching)
+					  bool using_pgpriv2, bool caching)
 {
 	if (caching)
 		__fscache_write_to_cache(cookie, mapping, start, len, i_size,
-					 term_func, term_func_priv, caching);
+					 term_func, term_func_priv,
+					 using_pgpriv2, caching);
 	else if (term_func)
 		term_func(term_func_priv, -ENOBUFS, false);