nfsd: increase DRC cache limit

BugLink: https://bugs.launchpad.net/bugs/1840081

[ Upstream commit 44d8660d ]

An NFSv4.1+ client negotiates the size of its duplicate reply cache size
in the initial CREATE_SESSION request.  The server preallocates the
memory for the duplicate reply cache to ensure that we'll never fail to
record the response to a nonidempotent operation.

To prevent a few CREATE_SESSIONs from consuming all of memory we set an
upper limit based on nr_free_buffer_pages().  1/2^10 has been too
limiting in practice; 1/2^7 is still less than one percent.
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

fs/nfsd/nfssvc.c

@@ -360,7 +360,7 @@ void nfsd_reset_versions(void)
  */
 static void set_max_drc(void)
 {
-	#define NFSD_DRC_SIZE_SHIFT	10
+	#define NFSD_DRC_SIZE_SHIFT	7
 	nfsd_drc_max_mem = (nr_free_buffer_pages()
 					>> NFSD_DRC_SIZE_SHIFT) * PAGE_SIZE;
 	nfsd_drc_mem_used = 0;