ceph: support ceph_pagelist for message payload

The ceph_pagelist is a simple list of whole pages, strung together via
their lru list_head.  It facilitates encoding to a "buffer" of unknown
size.  Allow its use in place of the ceph_msg page vector.

This will be used to fix the huge buffer preallocation woes of MDS
reconnection.

Signed-off-by: Sage Weil <sage@newdream.net>

1 files changed, 54 insertions, 0 deletions

diff --git a/fs/ceph/pagelist.c b/fs/ceph/pagelist.c
new file mode 100644
index 000000000000..370e93695474
--- /dev/null
+++ b/fs/ceph/pagelist.c
@@ -0,0 +1,54 @@
+
+#include <linux/pagemap.h>
+#include <linux/highmem.h>
+
+#include "pagelist.h"
+
+int ceph_pagelist_release(struct ceph_pagelist *pl)
+{
+        if (pl->mapped_tail)
+                kunmap(pl->mapped_tail);
+        while (!list_empty(&pl->head)) {
+                struct page *page = list_first_entry(&pl->head, struct page,
+                                                     lru);
+                list_del(&page->lru);
+                __free_page(page);
+        }
+        return 0;
+}
+
+static int ceph_pagelist_addpage(struct ceph_pagelist *pl)
+{
+        struct page *page = alloc_page(GFP_NOFS);
+        if (!page)
+                return -ENOMEM;
+        pl->room += PAGE_SIZE;
+        list_add_tail(&page->lru, &pl->head);
+        if (pl->mapped_tail)
+                kunmap(pl->mapped_tail);
+        pl->mapped_tail = kmap(page);
+        return 0;
+}
+
+int ceph_pagelist_append(struct ceph_pagelist *pl, void *buf, size_t len)
+{
+        while (pl->room < len) {
+                size_t bit = pl->room;
+                int ret;
+
+                memcpy(pl->mapped_tail + (pl->length & ~PAGE_CACHE_MASK),
+                       buf, bit);
+                pl->length += bit;
+                pl->room -= bit;
+                buf += bit;
+                len -= bit;
+                ret = ceph_pagelist_addpage(pl);
+                if (ret)
+                        return ret;
+        }
+
+        memcpy(pl->mapped_tail + (pl->length & ~PAGE_CACHE_MASK), buf, len);
+        pl->length += len;
+        pl->room -= len;
+        return 0;
+}