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Subject: [PATCH 28/64] fscache: Provide a function to note the release of a
 page
From:   David Howells <dhowells@redhat.com>
To:     linux-cachefs@redhat.com
Cc:     dhowells@redhat.com, Trond Myklebust <trondmy@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Steve French <sfrench@samba.org>,
        Dominique Martinet <asmadeus@codewreck.org>,
        Jeff Layton <jlayton@kernel.org>,
        Matthew Wilcox <willy@infradead.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Omar Sandoval <osandov@osandov.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org,
        linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org,
        v9fs-developer@lists.sourceforge.net,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Date:   Mon, 29 Nov 2021 14:29:31 +0000
Message-ID: <163819617128.215744.4725572296135656508.stgit@warthog.procyon.org.uk>
In-Reply-To: <163819575444.215744.318477214576928110.stgit@warthog.procyon.org.uk>
References: <163819575444.215744.318477214576928110.stgit@warthog.procyon.org.uk>
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Provide a function to be called from a network filesystem's releasepage
method to indicate that a page has been released that might have been a
reflection of data upon the server - and now that data must be reloaded
from the server or the cache.

This is used to end an optimisation for empty files, in particular files
that have just been created locally, whereby we know there cannot yet be
any data that we would need to read from the server or the cache.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-cachefs@redhat.com
---

 include/linux/fscache.h |   16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/include/linux/fscache.h b/include/linux/fscache.h
index 912ed2d7462a..1de789f0dd26 100644
--- a/include/linux/fscache.h
+++ b/include/linux/fscache.h
@@ -599,4 +599,20 @@ static inline void fscache_clear_inode_writeback(struct fscache_cookie *cookie,
 	}
 }
 
+/**
+ * fscache_note_page_release - Note that a netfs page got released
+ * @cookie: The cookie corresponding to the file
+ *
+ * Note that a page that has been copied to the cache has been released.  This
+ * means that future reads will need to look in the cache to see if it's there.
+ */
+static inline
+void fscache_note_page_release(struct fscache_cookie *cookie)
+{
+	if (cookie &&
+	    test_bit(FSCACHE_COOKIE_HAVE_DATA, &cookie->flags) &&
+	    test_bit(FSCACHE_COOKIE_NO_DATA_TO_READ, &cookie->flags))
+		clear_bit(FSCACHE_COOKIE_NO_DATA_TO_READ, &cookie->flags);
+}
+
 #endif /* _LINUX_FSCACHE_H */