net/smc: Allow SMC-D 1MB DMB allocations

Commit a3fe3d0 ("net/smc: introduce sg-logic for RMBs") introduced
a restriction for RMB allocations as used by SMC-R. However, SMC-D does
not use scatter-gather lists to back its DMBs, yet it was limited by
this restriction, still.
This patch exempts SMC, but limits allocations to the maximum RMB/DMB
size respectively.

Signed-off-by: Stefan Raspl <raspl@linux.ibm.com>
Signed-off-by: Guvenc Gulce <guvenc@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/smc/smc_core.c

@@ -1752,21 +1752,30 @@ int smc_conn_create(struct smc_sock *smc, struct smc_init_info *ini)
 	return rc;
 }
 
-/* convert the RMB size into the compressed notation - minimum 16K.
+#define SMCD_DMBE_SIZES		6 /* 0 -> 16KB, 1 -> 32KB, .. 6 -> 1MB */
+#define SMCR_RMBE_SIZES		5 /* 0 -> 16KB, 1 -> 32KB, .. 5 -> 512KB */
+
+/* convert the RMB size into the compressed notation (minimum 16K, see
+ * SMCD/R_DMBE_SIZES.
  * In contrast to plain ilog2, this rounds towards the next power of 2,
  * so the socket application gets at least its desired sndbuf / rcvbuf size.
  */
-static u8 smc_compress_bufsize(int size)
+static u8 smc_compress_bufsize(int size, bool is_smcd, bool is_rmb)
 {
+	const unsigned int max_scat = SG_MAX_SINGLE_ALLOC * PAGE_SIZE;
 	u8 compressed;
 
 	if (size <= SMC_BUF_MIN_SIZE)
 		return 0;
 
-	size = (size - 1) >> 14;
-	compressed = ilog2(size) + 1;
-	if (compressed >= SMC_RMBE_SIZES)
-		compressed = SMC_RMBE_SIZES - 1;
+	size = (size - 1) >> 14;  /* convert to 16K multiple */
+	compressed = min_t(u8, ilog2(size) + 1,
+			   is_smcd ? SMCD_DMBE_SIZES : SMCR_RMBE_SIZES);
+
+	if (!is_smcd && is_rmb)
+		/* RMBs are backed by & limited to max size of scatterlists */
+		compressed = min_t(u8, compressed, ilog2(max_scat >> 14));
+
 	return compressed;
 }
 
@@ -1982,17 +1991,12 @@ static int smcr_buf_map_usable_links(struct smc_link_group *lgr,
 	return rc;
 }
 
-#define SMCD_DMBE_SIZES		6 /* 0 -> 16KB, 1 -> 32KB, .. 6 -> 1MB */
-
 static struct smc_buf_desc *smcd_new_buf_create(struct smc_link_group *lgr,
 						bool is_dmb, int bufsize)
 {
 	struct smc_buf_desc *buf_desc;
 	int rc;
 
-	if (smc_compress_bufsize(bufsize) > SMCD_DMBE_SIZES)
-		return ERR_PTR(-EAGAIN);
-
 	/* try to alloc a new DMB */
 	buf_desc = kzalloc(sizeof(*buf_desc), GFP_KERNEL);
 	if (!buf_desc)
@@ -2041,9 +2045,8 @@ static int __smc_buf_create(struct smc_sock *smc, bool is_smcd, bool is_rmb)
 		/* use socket send buffer size (w/o overhead) as start value */
 		sk_buf_size = smc->sk.sk_sndbuf / 2;
 
-	for (bufsize_short = smc_compress_bufsize(sk_buf_size);
+	for (bufsize_short = smc_compress_bufsize(sk_buf_size, is_smcd, is_rmb);
 	     bufsize_short >= 0; bufsize_short--) {
-
 		if (is_rmb) {
 			lock = &lgr->rmbs_lock;
 			buf_list = &lgr->rmbs[bufsize_short];
@@ -2052,8 +2055,6 @@ static int __smc_buf_create(struct smc_sock *smc, bool is_smcd, bool is_rmb)
 			buf_list = &lgr->sndbufs[bufsize_short];
 		}
 		bufsize = smc_uncompress_bufsize(bufsize_short);
-		if ((1 << get_order(bufsize)) > SG_MAX_SINGLE_ALLOC)
-			continue;
 
 		/* check for reusable slot in the link group */
 		buf_desc = smc_buf_get_slot(bufsize_short, lock, buf_list);