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, 17 insertions, 3 deletions

diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 100cbb261269..f5e9c5f84a0c 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -143,6 +143,8 @@ struct netfs_inode {
 #define NETFS_ICTX_UNBUFFERED	1		/* I/O should not use the pagecache */
 #define NETFS_ICTX_WRITETHROUGH	2		/* Write-through caching */
 #define NETFS_ICTX_NO_WRITE_STREAMING	3	/* Don't engage in write-streaming */
+#define NETFS_ICTX_USE_PGPRIV2	31		/* [DEPRECATED] Use PG_private_2 to mark
+						 * write to cache on read */
 };
 
 /*
@@ -165,16 +167,25 @@ struct netfs_folio {
 	unsigned int		dirty_len;	/* Write-streaming dirty data length */
 };
 #define NETFS_FOLIO_INFO	0x1UL	/* OR'd with folio->private. */
+#define NETFS_FOLIO_COPY_TO_CACHE ((struct netfs_group *)0x356UL) /* Write to the cache only */
 
-static inline struct netfs_folio *netfs_folio_info(struct folio *folio)
+static inline bool netfs_is_folio_info(const void *priv)
 {
-	void *priv = folio_get_private(folio);
+	return (unsigned long)priv & NETFS_FOLIO_INFO;
+}
 
-	if ((unsigned long)priv & NETFS_FOLIO_INFO)
+static inline struct netfs_folio *__netfs_folio_info(const void *priv)
+{
+	if (netfs_is_folio_info(priv))
 		return (struct netfs_folio *)((unsigned long)priv & ~NETFS_FOLIO_INFO);
 	return NULL;
 }
 
+static inline struct netfs_folio *netfs_folio_info(struct folio *folio)
+{
+	return __netfs_folio_info(folio_get_private(folio));
+}
+
 static inline struct netfs_group *netfs_folio_group(struct folio *folio)
 {
 	struct netfs_folio *finfo;
@@ -230,6 +241,7 @@ enum netfs_io_origin {
 	NETFS_READAHEAD,		/* This read was triggered by readahead */
 	NETFS_READPAGE,			/* This read is a synchronous read */
 	NETFS_READ_FOR_WRITE,		/* This read is to prepare a write */
+	NETFS_COPY_TO_CACHE,		/* This write is to copy a read to the cache */
 	NETFS_WRITEBACK,		/* This write was triggered by writepages */
 	NETFS_WRITETHROUGH,		/* This write was made by netfs_perform_write() */
 	NETFS_LAUNDER_WRITE,		/* This is triggered by ->launder_folio() */
@@ -287,6 +299,8 @@ struct netfs_io_request {
 #define NETFS_RREQ_UPLOAD_TO_SERVER	8	/* Need to write to the server */
 #define NETFS_RREQ_NONBLOCK		9	/* Don't block if possible (O_NONBLOCK) */
 #define NETFS_RREQ_BLOCKED		10	/* We blocked */
+#define NETFS_RREQ_USE_PGPRIV2		31	/* [DEPRECATED] Use PG_private_2 to mark
+						 * write to cache on read */
 	const struct netfs_request_ops *netfs_ops;
 	void (*cleanup)(struct netfs_io_request *req);
 };