ceph: add pagelist_reserve, pagelist_truncate, pagelist_set_cursor

These facilitate preallocation of pages so that we can encode into the pagelist
in an atomic context.

Signed-off-by: Greg Farnum <gregf@hq.newdream.net>
Signed-off-by: Sage Weil <sage@newdream.net>

1 files changed, 97 insertions, 9 deletions

diff --git a/net/ceph/pagelist.c b/net/ceph/pagelist.c
index 3b146cfac182..b8cbc456d0bb 100644
--- a/net/ceph/pagelist.c
+++ b/net/ceph/pagelist.c
@@ -7,35 +7,42 @@
 
 static void ceph_pagelist_unmap_tail(struct ceph_pagelist *pl)
 {
-        struct page *page = list_entry(pl->head.prev, struct page,
-                                       lru);
-        kunmap(page);
+        if (pl->mapped_tail) {
+                struct page *page = list_entry(pl->head.prev, struct page, lru);
+                kunmap(page);
+                pl->mapped_tail = NULL;
+        }
 }
 
 int ceph_pagelist_release(struct ceph_pagelist *pl)
 {
-        if (pl->mapped_tail)
-                ceph_pagelist_unmap_tail(pl);
-
+        ceph_pagelist_unmap_tail(pl);
         while (!list_empty(&pl->head)) {
                 struct page *page = list_first_entry(&pl->head, struct page,
                                                      lru);
                 list_del(&page->lru);
                 __free_page(page);
         }
+        ceph_pagelist_free_reserve(pl);
         return 0;
 }
 EXPORT_SYMBOL(ceph_pagelist_release);
 
 static int ceph_pagelist_addpage(struct ceph_pagelist *pl)
 {
-        struct page *page = __page_cache_alloc(GFP_NOFS);
+        struct page *page;
+
+        if (!pl->num_pages_free) {
+                page = __page_cache_alloc(GFP_NOFS);
+        } else {
+                page = list_first_entry(&pl->free_list, struct page, lru);
+                list_del(&page->lru);
+        }
         if (!page)
                 return -ENOMEM;
         pl->room += PAGE_SIZE;
+        ceph_pagelist_unmap_tail(pl);
         list_add_tail(&page->lru, &pl->head);
-        if (pl->mapped_tail)
-                ceph_pagelist_unmap_tail(pl);
         pl->mapped_tail = kmap(page);
         return 0;
 }
@@ -63,3 +70,84 @@ int ceph_pagelist_append(struct ceph_pagelist *pl, const void *buf, size_t len)
         return 0;
 }
 EXPORT_SYMBOL(ceph_pagelist_append);
+
+/**
+ * Allocate enough pages for a pagelist to append the given amount
+ * of data without without allocating.
+ * Returns: 0 on success, -ENOMEM on error.
+ */
+int ceph_pagelist_reserve(struct ceph_pagelist *pl, size_t space)
+{
+        if (space <= pl->room)
+                return 0;
+        space -= pl->room;
+        space = (space + PAGE_SIZE - 1) >> PAGE_SHIFT;   /* conv to num pages */
+
+        while (space > pl->num_pages_free) {
+                struct page *page = __page_cache_alloc(GFP_NOFS);
+                if (!page)
+                        return -ENOMEM;
+                list_add_tail(&page->lru, &pl->free_list);
+                ++pl->num_pages_free;
+        }
+        return 0;
+}
+EXPORT_SYMBOL(ceph_pagelist_reserve);
+
+/**
+ * Free any pages that have been preallocated.
+ */
+int ceph_pagelist_free_reserve(struct ceph_pagelist *pl)
+{
+        while (!list_empty(&pl->free_list)) {
+                struct page *page = list_first_entry(&pl->free_list,
+                                                     struct page, lru);
+                list_del(&page->lru);
+                __free_page(page);
+                --pl->num_pages_free;
+        }
+        BUG_ON(pl->num_pages_free);
+        return 0;
+}
+EXPORT_SYMBOL(ceph_pagelist_free_reserve);
+
+/**
+ * Create a truncation point.
+ */
+void ceph_pagelist_set_cursor(struct ceph_pagelist *pl,
+                              struct ceph_pagelist_cursor *c)
+{
+        c->pl = pl;
+        c->page_lru = pl->head.prev;
+        c->room = pl->room;
+}
+EXPORT_SYMBOL(ceph_pagelist_set_cursor);
+
+/**
+ * Truncate a pagelist to the given point. Move extra pages to reserve.
+ * This won't sleep.
+ * Returns: 0 on success,
+ *          -EINVAL if the pagelist doesn't match the trunc point pagelist
+ */
+int ceph_pagelist_truncate(struct ceph_pagelist *pl,
+                           struct ceph_pagelist_cursor *c)
+{
+        struct page *page;
+
+        if (pl != c->pl)
+                return -EINVAL;
+        ceph_pagelist_unmap_tail(pl);
+        while (pl->head.prev != c->page_lru) {
+                page = list_entry(pl->head.prev, struct page, lru);
+                list_del(&page->lru);                /* remove from pagelist */
+                list_add_tail(&page->lru, &pl->free_list); /* add to reserve */
+                ++pl->num_pages_free;
+        }
+        pl->room = c->room;
+        if (!list_empty(&pl->head)) {
+                page = list_entry(pl->head.prev, struct page, lru);
+                pl->mapped_tail = kmap(page);
+        }
+        return 0;
+}
+EXPORT_SYMBOL(ceph_pagelist_truncate);