RDS: Message parsing

Parsing of newly-received RDS message headers (including ext.
headers) and copy-to/from-user routines.

page.c implements a per-cpu page remainder cache, to reduce the
number of allocations needed for small datagrams.
Signed-off-by: Andy Grover <andy.grover@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/rds/page.c

+/*
+ * Copyright (c) 2006 Oracle.  All rights reserved.
+ *
+ * This software is available to you under a choice of one of two
+ * licenses.  You may choose to be licensed under the terms of the GNU
+ * General Public License (GPL) Version 2, available from the file
+ * COPYING in the main directory of this source tree, or the
+ * OpenIB.org BSD license below:
+ *
+ *     Redistribution and use in source and binary forms, with or
+ *     without modification, are permitted provided that the following
+ *     conditions are met:
+ *
+ *      - Redistributions of source code must retain the above
+ *        copyright notice, this list of conditions and the following
+ *        disclaimer.
+ *
+ *      - Redistributions in binary form must reproduce the above
+ *        copyright notice, this list of conditions and the following
+ *        disclaimer in the documentation and/or other materials
+ *        provided with the distribution.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ */
+#include <linux/highmem.h>
+
+#include "rds.h"
+
+struct rds_page_remainder {
+	struct page	*r_page;
+	unsigned long	r_offset;
+};
+
+DEFINE_PER_CPU(struct rds_page_remainder, rds_page_remainders) ____cacheline_aligned;
+
+/*
+ * returns 0 on success or -errno on failure.
+ *
+ * We don't have to worry about flush_dcache_page() as this only works
+ * with private pages.  If, say, we were to do directed receive to pinned
+ * user pages we'd have to worry more about cache coherence.  (Though
+ * the flush_dcache_page() in get_user_pages() would probably be enough).
+ */
+int rds_page_copy_user(struct page *page, unsigned long offset,
+		       void __user *ptr, unsigned long bytes,
+		       int to_user)
+{
+	unsigned long ret;
+	void *addr;
+
+	if (to_user)
+		rds_stats_add(s_copy_to_user, bytes);
+	else
+		rds_stats_add(s_copy_from_user, bytes);
+
+	addr = kmap_atomic(page, KM_USER0);
+	if (to_user)
+		ret = __copy_to_user_inatomic(ptr, addr + offset, bytes);
+	else
+		ret = __copy_from_user_inatomic(addr + offset, ptr, bytes);
+	kunmap_atomic(addr, KM_USER0);
+
+	if (ret) {
+		addr = kmap(page);
+		if (to_user)
+			ret = copy_to_user(ptr, addr + offset, bytes);
+		else
+			ret = copy_from_user(addr + offset, ptr, bytes);
+		kunmap(page);
+		if (ret)
+			return -EFAULT;
+	}
+
+	return 0;
+}
+
+/*
+ * Message allocation uses this to build up regions of a message.
+ *
+ * @bytes - the number of bytes needed.
+ * @gfp - the waiting behaviour of the allocation
+ *
+ * @gfp is always ored with __GFP_HIGHMEM.  Callers must be prepared to
+ * kmap the pages, etc.
+ *
+ * If @bytes is at least a full page then this just returns a page from
+ * alloc_page().
+ *
+ * If @bytes is a partial page then this stores the unused region of the
+ * page in a per-cpu structure.  Future partial-page allocations may be
+ * satisfied from that cached region.  This lets us waste less memory on
+ * small allocations with minimal complexity.  It works because the transmit
+ * path passes read-only page regions down to devices.  They hold a page
+ * reference until they are done with the region.
+ */
+int rds_page_remainder_alloc(struct scatterlist *scat, unsigned long bytes,
+			     gfp_t gfp)
+{
+	struct rds_page_remainder *rem;
+	unsigned long flags;
+	struct page *page;
+	int ret;
+
+	gfp |= __GFP_HIGHMEM;
+
+	/* jump straight to allocation if we're trying for a huge page */
+	if (bytes >= PAGE_SIZE) {
+		page = alloc_page(gfp);
+		if (page == NULL) {
+			ret = -ENOMEM;
+		} else {
+			sg_set_page(scat, page, PAGE_SIZE, 0);
+			ret = 0;
+		}
+		goto out;
+	}
+
+	rem = &per_cpu(rds_page_remainders, get_cpu());
+	local_irq_save(flags);
+
+	while (1) {
+		/* avoid a tiny region getting stuck by tossing it */
+		if (rem->r_page && bytes > (PAGE_SIZE - rem->r_offset)) {
+			rds_stats_inc(s_page_remainder_miss);
+			__free_page(rem->r_page);
+			rem->r_page = NULL;
+		}
+
+		/* hand out a fragment from the cached page */
+		if (rem->r_page && bytes <= (PAGE_SIZE - rem->r_offset)) {
+			sg_set_page(scat, rem->r_page, bytes, rem->r_offset);
+			get_page(sg_page(scat));
+
+			if (rem->r_offset != 0)
+				rds_stats_inc(s_page_remainder_hit);
+
+			rem->r_offset += bytes;
+			if (rem->r_offset == PAGE_SIZE) {
+				__free_page(rem->r_page);
+				rem->r_page = NULL;
+			}
+			ret = 0;
+			break;
+		}
+
+		/* alloc if there is nothing for us to use */
+		local_irq_restore(flags);
+		put_cpu();
+
+		page = alloc_page(gfp);
+
+		rem = &per_cpu(rds_page_remainders, get_cpu());
+		local_irq_save(flags);
+
+		if (page == NULL) {
+			ret = -ENOMEM;
+			break;
+		}
+
+		/* did someone race to fill the remainder before us? */
+		if (rem->r_page) {
+			__free_page(page);
+			continue;
+		}
+
+		/* otherwise install our page and loop around to alloc */
+		rem->r_page = page;
+		rem->r_offset = 0;
+	}
+
+	local_irq_restore(flags);
+	put_cpu();
+out:
+	rdsdebug("bytes %lu ret %d %p %u %u\n", bytes, ret,
+		 ret ? NULL : sg_page(scat), ret ? 0 : scat->offset,
+		 ret ? 0 : scat->length);
+	return ret;
+}
+
+static int rds_page_remainder_cpu_notify(struct notifier_block *self,
+					 unsigned long action, void *hcpu)
+{
+	struct rds_page_remainder *rem;
+	long cpu = (long)hcpu;
+
+	rem = &per_cpu(rds_page_remainders, cpu);
+
+	rdsdebug("cpu %ld action 0x%lx\n", cpu, action);
+
+	switch (action) {
+	case CPU_DEAD:
+		if (rem->r_page)
+			__free_page(rem->r_page);
+		rem->r_page = NULL;
+		break;
+	}
+
+	return 0;
+}
+
+static struct notifier_block rds_page_remainder_nb = {
+	.notifier_call = rds_page_remainder_cpu_notify,
+};
+
+void rds_page_exit(void)
+{
+	int i;
+
+	for_each_possible_cpu(i)
+		rds_page_remainder_cpu_notify(&rds_page_remainder_nb,
+					      (unsigned long)CPU_DEAD,
+					      (void *)(long)i);
+}