ocfs2: allocation reservations

This patch improves Ocfs2 allocation policy by allowing an inode to
reserve a portion of the local alloc bitmap for itself. The reserved
portion (allocation window) is advisory in that other allocation
windows might steal it if the local alloc bitmap becomes
full. Otherwise, the reservations are honored and guaranteed to be
free. When the local alloc window is moved to a different portion of
the bitmap, existing reservations are discarded.

Reservation windows are represented internally by a red-black
tree. Within that tree, each node represents the reservation window of
one inode. An LRU of active reservations is also maintained. When new
data is written, we allocate it from the inodes window. When all bits
in a window are exhausted, we allocate a new one as close to the
previous one as possible. Should we not find free space, an existing
reservation is pulled off the LRU and cannibalized.

Signed-off-by: Mark Fasheh <mfasheh@suse.com>

1 files changed, 849 insertions, 0 deletions

diff --git a/fs/ocfs2/reservations.c b/fs/ocfs2/reservations.c
new file mode 100644
index 000000000000..79642d608210
--- /dev/null
+++ b/fs/ocfs2/reservations.c
@@ -0,0 +1,849 @@
+/* -*- mode: c; c-basic-offset: 8; -*-
+ * vim: noexpandtab sw=8 ts=8 sts=0:
+ *
+ * reservations.c
+ *
+ * Allocation reservations implementation
+ *
+ * Some code borrowed from fs/ext3/balloc.c and is:
+ *
+ * Copyright (C) 1992, 1993, 1994, 1995
+ * Remy Card (card@masi.ibp.fr)
+ * Laboratoire MASI - Institut Blaise Pascal
+ * Universite Pierre et Marie Curie (Paris VI)
+ *
+ * The rest is copyright (C) 2010 Novell.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#include <linux/fs.h>
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/highmem.h>
+#include <linux/bitops.h>
+#include <linux/list.h>
+
+#define MLOG_MASK_PREFIX ML_RESERVATIONS
+#include <cluster/masklog.h>
+
+#include "ocfs2.h"
+
+#ifdef CONFIG_OCFS2_DEBUG_FS
+#define OCFS2_CHECK_RESERVATIONS
+#endif
+
+DEFINE_SPINLOCK(resv_lock);
+
+#define OCFS2_MIN_RESV_WINDOW_BITS      8
+#define OCFS2_MAX_RESV_WINDOW_BITS      1024
+
+static unsigned int ocfs2_resv_window_bits(struct ocfs2_reservation_map *resmap,
+                                           struct ocfs2_alloc_reservation *resv)
+{
+        struct ocfs2_super *osb = resmap->m_osb;
+        unsigned int bits;
+
+        /* 8, 16, 32, 64, 128, 256, 512, 1024 */
+        bits = 4 << osb->osb_resv_level;
+
+        return bits;
+}
+
+static inline unsigned int ocfs2_resv_end(struct ocfs2_alloc_reservation *resv)
+{
+        if (resv->r_len)
+                return resv->r_start + resv->r_len - 1;
+        return resv->r_start;
+}
+
+static inline int ocfs2_resv_empty(struct ocfs2_alloc_reservation *resv)
+{
+        return !!(resv->r_len == 0);
+}
+
+static inline int ocfs2_resmap_disabled(struct ocfs2_reservation_map *resmap)
+{
+        if (resmap->m_osb->osb_resv_level == 0)
+                return 1;
+        return 0;
+}
+
+static void ocfs2_dump_resv(struct ocfs2_reservation_map *resmap)
+{
+        struct ocfs2_super *osb = resmap->m_osb;
+        struct rb_node *node;
+        struct ocfs2_alloc_reservation *resv;
+        int i = 0;
+
+        mlog(ML_NOTICE, "Dumping resmap for device %s. Bitmap length: %u\n",
+             osb->dev_str, resmap->m_bitmap_len);
+
+        node = rb_first(&resmap->m_reservations);
+        while (node) {
+                resv = rb_entry(node, struct ocfs2_alloc_reservation, r_node);
+
+                mlog(ML_NOTICE, "start: %u\tend: %u\tlen: %u\tlast_start: %u"
+                     "\tlast_len: %u\n", resv->r_start,
+                     ocfs2_resv_end(resv), resv->r_len, resv->r_last_start,
+                     resv->r_last_len);
+
+                node = rb_next(node);
+                i++;
+        }
+
+        mlog(ML_NOTICE, "%d reservations found. LRU follows\n", i);
+
+        i = 0;
+        list_for_each_entry(resv, &resmap->m_lru, r_lru) {
+                mlog(ML_NOTICE, "LRU(%d) start: %u\tend: %u\tlen: %u\t"
+                     "last_start: %u\tlast_len: %u\n", i, resv->r_start,
+                     ocfs2_resv_end(resv), resv->r_len, resv->r_last_start,
+                     resv->r_last_len);
+
+                i++;
+        }
+}
+
+#ifdef OCFS2_CHECK_RESERVATIONS
+static int ocfs2_validate_resmap_bits(struct ocfs2_reservation_map *resmap,
+                                      int i,
+                                      struct ocfs2_alloc_reservation *resv)
+{
+        char *disk_bitmap = resmap->m_disk_bitmap;
+        unsigned int start = resv->r_start;
+        unsigned int end = ocfs2_resv_end(resv);
+
+        while (start <= end) {
+                if (ocfs2_test_bit(start, disk_bitmap)) {
+                        mlog(ML_ERROR,
+                             "reservation %d covers an allocated area "
+                             "starting at bit %u!\n", i, start);
+                        return 1;
+                }
+
+                start++;
+        }
+        return 0;
+}
+
+static void ocfs2_check_resmap(struct ocfs2_reservation_map *resmap)
+{
+        unsigned int off = 0;
+        int i = 0;
+        struct rb_node *node;
+        struct ocfs2_alloc_reservation *resv;
+
+        node = rb_first(&resmap->m_reservations);
+        while (node) {
+                resv = rb_entry(node, struct ocfs2_alloc_reservation, r_node);
+
+                if (i > 0 && resv->r_start <= off) {
+                        mlog(ML_ERROR, "reservation %d has bad start off!\n",
+                             i);
+                        goto bad;
+                }
+
+                if (resv->r_len == 0) {
+                        mlog(ML_ERROR, "reservation %d has no length!\n",
+                             i);
+                        goto bad;
+                }
+
+                if (resv->r_start > ocfs2_resv_end(resv)) {
+                        mlog(ML_ERROR, "reservation %d has invalid range!\n",
+                             i);
+                        goto bad;
+                }
+
+                if (ocfs2_resv_end(resv) >= resmap->m_bitmap_len) {
+                        mlog(ML_ERROR, "reservation %d extends past bitmap!\n",
+                             i);
+                        goto bad;
+                }
+
+                if (ocfs2_validate_resmap_bits(resmap, i, resv))
+                        goto bad;
+
+                off = ocfs2_resv_end(resv);
+                node = rb_next(node);
+
+                i++;
+        }
+        return;
+
+bad:
+        ocfs2_dump_resv(resmap);
+        BUG();
+}
+#else
+static inline void ocfs2_check_resmap(struct ocfs2_reservation_map *resmap)
+{
+
+}
+#endif
+
+void ocfs2_resv_init_once(struct ocfs2_alloc_reservation *resv)
+{
+        memset(resv, 0, sizeof(*resv));
+        INIT_LIST_HEAD(&resv->r_lru);
+}
+
+void ocfs2_resv_set_type(struct ocfs2_alloc_reservation *resv,
+                         unsigned int flags)
+{
+        BUG_ON(flags & ~OCFS2_RESV_TYPES);
+
+        resv->r_flags |= flags;
+}
+
+int ocfs2_resmap_init(struct ocfs2_super *osb,
+                      struct ocfs2_reservation_map *resmap)
+{
+        memset(resmap, 0, sizeof(*resmap));
+
+        resmap->m_osb = osb;
+        resmap->m_reservations = RB_ROOT;
+        /* m_bitmap_len is initialized to zero by the above memset. */
+        INIT_LIST_HEAD(&resmap->m_lru);
+
+        return 0;
+}
+
+static void ocfs2_resv_mark_lru(struct ocfs2_reservation_map *resmap,
+                                struct ocfs2_alloc_reservation *resv)
+{
+        assert_spin_locked(&resv_lock);
+
+        if (!list_empty(&resv->r_lru))
+                list_del_init(&resv->r_lru);
+
+        list_add_tail(&resv->r_lru, &resmap->m_lru);
+}
+
+static void __ocfs2_resv_trunc(struct ocfs2_alloc_reservation *resv)
+{
+        resv->r_len = 0;
+        resv->r_start = 0;
+}
+
+static void ocfs2_resv_remove(struct ocfs2_reservation_map *resmap,
+                              struct ocfs2_alloc_reservation *resv)
+{
+        if (resv->r_flags & OCFS2_RESV_FLAG_INUSE) {
+                list_del_init(&resv->r_lru);
+                rb_erase(&resv->r_node, &resmap->m_reservations);
+                resv->r_flags &= ~OCFS2_RESV_FLAG_INUSE;
+        }
+}
+
+static void __ocfs2_resv_discard(struct ocfs2_reservation_map *resmap,
+                                 struct ocfs2_alloc_reservation *resv)
+{
+        assert_spin_locked(&resv_lock);
+
+        __ocfs2_resv_trunc(resv);
+        /*
+         * last_len and last_start no longer make sense if
+         * we're changing the range of our allocations.
+         */
+        resv->r_last_len = resv->r_last_start = 0;
+
+        ocfs2_resv_remove(resmap, resv);
+}
+
+/* does nothing if 'resv' is null */
+void ocfs2_resv_discard(struct ocfs2_reservation_map *resmap,
+                        struct ocfs2_alloc_reservation *resv)
+{
+        if (resv) {
+                spin_lock(&resv_lock);
+                __ocfs2_resv_discard(resmap, resv);
+                spin_unlock(&resv_lock);
+        }
+}
+
+static void ocfs2_resmap_clear_all_resv(struct ocfs2_reservation_map *resmap)
+{
+        struct rb_node *node;
+        struct ocfs2_alloc_reservation *resv;
+
+        assert_spin_locked(&resv_lock);
+
+        while ((node = rb_last(&resmap->m_reservations)) != NULL) {
+                resv = rb_entry(node, struct ocfs2_alloc_reservation, r_node);
+
+                __ocfs2_resv_discard(resmap, resv);
+        }
+}
+
+void ocfs2_resmap_restart(struct ocfs2_reservation_map *resmap,
+                          unsigned int clen, char *disk_bitmap)
+{
+        if (ocfs2_resmap_disabled(resmap))
+                return;
+
+        spin_lock(&resv_lock);
+
+        ocfs2_resmap_clear_all_resv(resmap);
+        resmap->m_bitmap_len = clen;
+        resmap->m_disk_bitmap = disk_bitmap;
+
+        spin_unlock(&resv_lock);
+}
+
+void ocfs2_resmap_uninit(struct ocfs2_reservation_map *resmap)
+{
+        /* Does nothing for now. Keep this around for API symmetry */
+}
+
+static void ocfs2_resv_insert(struct ocfs2_reservation_map *resmap,
+                              struct ocfs2_alloc_reservation *new)
+{
+        struct rb_root *root = &resmap->m_reservations;
+        struct rb_node *parent = NULL;
+        struct rb_node **p = &root->rb_node;
+        struct ocfs2_alloc_reservation *tmp;
+
+        assert_spin_locked(&resv_lock);
+
+        mlog(0, "Insert reservation start: %u len: %u\n", new->r_start,
+             new->r_len);
+
+        while (*p) {
+                parent = *p;
+
+                tmp = rb_entry(parent, struct ocfs2_alloc_reservation, r_node);
+
+                if (new->r_start < tmp->r_start) {
+                        p = &(*p)->rb_left;
+
+                        /*
+                         * This is a good place to check for
+                         * overlapping reservations.
+                         */
+                        BUG_ON(ocfs2_resv_end(new) >= tmp->r_start);
+                } else if (new->r_start > ocfs2_resv_end(tmp)) {
+                        p = &(*p)->rb_right;
+                } else {
+                        /* This should never happen! */
+                        mlog(ML_ERROR, "Duplicate reservation window!\n");
+                        BUG();
+                }
+        }
+
+        rb_link_node(&new->r_node, parent, p);
+        rb_insert_color(&new->r_node, root);
+        new->r_flags |= OCFS2_RESV_FLAG_INUSE;
+
+        ocfs2_resv_mark_lru(resmap, new);
+
+        ocfs2_check_resmap(resmap);
+}
+
+/**
+ * ocfs2_find_resv_lhs() - find the window which contains goal
+ * @resmap: reservation map to search
+ * @goal: which bit to search for
+ *
+ * If a window containing that goal is not found, we return the window
+ * which comes before goal. Returns NULL on empty rbtree or no window
+ * before goal.
+ */
+static struct ocfs2_alloc_reservation *
+ocfs2_find_resv_lhs(struct ocfs2_reservation_map *resmap, unsigned int goal)
+{
+        struct ocfs2_alloc_reservation *resv = NULL;
+        struct ocfs2_alloc_reservation *prev_resv = NULL;
+        struct rb_node *node = resmap->m_reservations.rb_node;
+        struct rb_node *prev = NULL;
+
+        assert_spin_locked(&resv_lock);
+
+        if (!node)
+                return NULL;
+
+        node = rb_first(&resmap->m_reservations);
+        while (node) {
+                resv = rb_entry(node, struct ocfs2_alloc_reservation, r_node);
+
+                if (resv->r_start <= goal && ocfs2_resv_end(resv) >= goal)
+                        break;
+
+                /* Check if we overshot the reservation just before goal? */
+                if (resv->r_start > goal) {
+                        resv = prev_resv;
+                        break;
+                }
+
+                prev_resv = resv;
+                prev = node;
+                node = rb_next(node);
+        }
+
+        return resv;
+}
+
+/*
+ * We are given a range within the bitmap, which corresponds to a gap
+ * inside the reservations tree (search_start, search_len). The range
+ * can be anything from the whole bitmap, to a gap between
+ * reservations.
+ *
+ * The start value of *rstart is insignificant.
+ *
+ * This function searches the bitmap range starting at search_start
+ * with length csearch_len for a set of contiguous free bits. We try
+ * to find up to 'wanted' bits, but can sometimes return less.
+ *
+ * Returns the length of allocation, 0 if no free bits are found.
+ *
+ * *cstart and *clen will also be populated with the result.
+ */
+static int ocfs2_resmap_find_free_bits(struct ocfs2_reservation_map *resmap,
+                                       unsigned int wanted,
+                                       unsigned int search_start,
+                                       unsigned int search_len,
+                                       unsigned int *rstart,
+                                       unsigned int *rlen)
+{
+        void *bitmap = resmap->m_disk_bitmap;
+        unsigned int best_start, best_len = 0;
+        int offset, start, found;
+
+        mlog(0, "Find %u bits within range (%u, len %u) resmap len: %u\n",
+             wanted, search_start, search_len, resmap->m_bitmap_len);
+
+        found = best_start = best_len = 0;
+
+        start = search_start;
+        while ((offset = ocfs2_find_next_zero_bit(bitmap, resmap->m_bitmap_len,
+                                                 start)) != -1) {
+                /* Search reached end of the region */
+                if (offset >= (search_start + search_len))
+                        break;
+
+                if (offset == start) {
+                        /* we found a zero */
+                        found++;
+                        /* move start to the next bit to test */
+                        start++;
+                } else {
+                        /* got a zero after some ones */
+                        found = 1;
+                        start = offset + 1;
+                }
+                if (found > best_len) {
+                        best_len = found;
+                        best_start = start - found;
+                }
+
+                if (found >= wanted)
+                        break;
+        }
+
+        if (best_len == 0)
+                return 0;
+
+        if (best_len >= wanted)
+                best_len = wanted;
+
+        *rlen = best_len;
+        *rstart = best_start;
+
+        mlog(0, "Found start: %u len: %u\n", best_start, best_len);
+
+        return *rlen;
+}
+
+static void __ocfs2_resv_find_window(struct ocfs2_reservation_map *resmap,
+                                     struct ocfs2_alloc_reservation *resv,
+                                     unsigned int goal, unsigned int wanted)
+{
+        struct rb_root *root = &resmap->m_reservations;
+        unsigned int gap_start, gap_end, gap_len;
+        struct ocfs2_alloc_reservation *prev_resv, *next_resv;
+        struct rb_node *prev, *next;
+        unsigned int cstart, clen;
+        unsigned int best_start = 0, best_len = 0;
+
+        /*
+         * Nasty cases to consider:
+         *
+         * - rbtree is empty
+         * - our window should be first in all reservations
+         * - our window should be last in all reservations
+         * - need to make sure we don't go past end of bitmap
+         */
+
+        mlog(0, "resv start: %u resv end: %u goal: %u wanted: %u\n",
+             resv->r_start, ocfs2_resv_end(resv), goal, wanted);
+
+        assert_spin_locked(&resv_lock);
+
+        if (RB_EMPTY_ROOT(root)) {
+                /*
+                 * Easiest case - empty tree. We can just take
+                 * whatever window of free bits we want.
+                 */
+
+                mlog(0, "Empty root\n");
+
+                clen = ocfs2_resmap_find_free_bits(resmap, wanted, goal,
+                                                   resmap->m_bitmap_len - goal,
+                                                   &cstart, &clen);
+
+                /*
+                 * This should never happen - the local alloc window
+                 * will always have free bits when we're called.
+                 */
+                BUG_ON(goal == 0 && clen == 0);
+
+                if (clen == 0)
+                        return;
+
+                resv->r_start = cstart;
+                resv->r_len = clen;
+
+                ocfs2_resv_insert(resmap, resv);
+                return;
+        }
+
+        prev_resv = ocfs2_find_resv_lhs(resmap, goal);
+
+        if (prev_resv == NULL) {
+                mlog(0, "Goal on LHS of leftmost window\n");
+
+                /*
+                 * A NULL here means that the search code couldn't
+                 * find a window that starts before goal.
+                 *
+                 * However, we can take the first window after goal,
+                 * which is also by definition, the leftmost window in
+                 * the entire tree. If we can find free bits in the
+                 * gap between goal and the LHS window, then the
+                 * reservation can safely be placed there.
+                 *
+                 * Otherwise we fall back to a linear search, checking
+                 * the gaps in between windows for a place to
+                 * allocate.
+                 */
+
+                next = rb_first(root);
+                next_resv = rb_entry(next, struct ocfs2_alloc_reservation,
+                                     r_node);
+
+                /*
+                 * The search should never return such a window. (see
+                 * comment above
+                 */
+                if (next_resv->r_start <= goal) {
+                        mlog(ML_ERROR, "goal: %u next_resv: start %u len %u\n",
+                             goal, next_resv->r_start, next_resv->r_len);
+                        ocfs2_dump_resv(resmap);
+                        BUG();
+                }
+
+                clen = ocfs2_resmap_find_free_bits(resmap, wanted, goal,
+                                                   next_resv->r_start - goal,
+                                                   &cstart, &clen);
+                if (clen) {
+                        best_len = clen;
+                        best_start = cstart;
+                        if (best_len == wanted)
+                                goto out_insert;
+                }
+
+                prev_resv = next_resv;
+                next_resv = NULL;
+        }
+
+        prev = &prev_resv->r_node;
+
+        /* Now we do a linear search for a window, starting at 'prev_rsv' */
+        while (1) {
+                next = rb_next(prev);
+                if (next) {
+                        mlog(0, "One more resv found in linear search\n");
+                        next_resv = rb_entry(next,
+                                             struct ocfs2_alloc_reservation,
+                                             r_node);
+
+                        gap_start = ocfs2_resv_end(prev_resv) + 1;
+                        gap_end = next_resv->r_start - 1;
+                        gap_len = gap_end - gap_start + 1;
+                } else {
+                        mlog(0, "No next node\n");
+                        /*
+                         * We're at the rightmost edge of the
+                         * tree. See if a reservation between this
+                         * window and the end of the bitmap will work.
+                         */
+                        gap_start = ocfs2_resv_end(prev_resv) + 1;
+                        gap_len = resmap->m_bitmap_len - gap_start;
+                        gap_end = resmap->m_bitmap_len - 1;
+                }
+
+                /*
+                 * No need to check this gap if we have already found
+                 * a larger region of free bits.
+                 */
+                if (gap_len <= best_len)
+                        goto next_resv;
+
+                clen = ocfs2_resmap_find_free_bits(resmap, wanted, gap_start,
+                                                   gap_len, &cstart, &clen);
+                if (clen == wanted) {
+                        best_len = clen;
+                        best_start = cstart;
+                        goto out_insert;
+                } else if (clen > best_len) {
+                        best_len = clen;
+                        best_start = cstart;
+                }
+
+next_resv:
+                if (!next)
+                        break;
+
+                prev = next;
+                prev_resv = rb_entry(prev, struct ocfs2_alloc_reservation,
+                                     r_node);
+        }
+
+out_insert:
+        if (best_len) {
+                resv->r_start = best_start;
+                resv->r_len = best_len;
+                ocfs2_resv_insert(resmap, resv);
+        }
+}
+
+static void ocfs2_cannibalize_resv(struct ocfs2_reservation_map *resmap,
+                                   struct ocfs2_alloc_reservation *resv,
+                                   unsigned int wanted)
+{
+        struct ocfs2_alloc_reservation *lru_resv;
+        int tmpwindow = !!(resv->r_flags & OCFS2_RESV_FLAG_TMP);
+        unsigned int min_bits;
+
+        if (!tmpwindow)
+                min_bits = ocfs2_resv_window_bits(resmap, resv) >> 1;
+        else
+                min_bits = wanted; /* We at know the temp window will use all
+                                    * of these bits */
+
+        /*
+         * Take the first reservation off the LRU as our 'target'. We
+         * don't try to be smart about it. There might be a case for
+         * searching based on size but I don't have enough data to be
+         * sure. --Mark (3/16/2010)
+         */
+        lru_resv = list_first_entry(&resmap->m_lru,
+                                    struct ocfs2_alloc_reservation, r_lru);
+
+        mlog(0, "lru resv: start: %u len: %u end: %u\n", lru_resv->r_start,
+             lru_resv->r_len, ocfs2_resv_end(lru_resv));
+
+        /*
+         * Cannibalize (some or all) of the target reservation and
+         * feed it to the current window.
+         */
+        if (lru_resv->r_len <= min_bits) {
+                /*
+                 * Discard completely if size is less than or equal to a
+                 * reasonable threshold - 50% of window bits for non temporary
+                 * windows.
+                 */
+                resv->r_start = lru_resv->r_start;
+                resv->r_len = lru_resv->r_len;
+
+                __ocfs2_resv_discard(resmap, lru_resv);
+        } else {
+                unsigned int shrink;
+                if (tmpwindow)
+                        shrink = min_bits;
+                else
+                        shrink = lru_resv->r_len / 2;
+
+                lru_resv->r_len -= shrink;
+
+                resv->r_start = ocfs2_resv_end(lru_resv) + 1;
+                resv->r_len = shrink;
+        }
+
+        mlog(0, "Reservation now looks like: r_start: %u r_end: %u "
+             "r_len: %u r_last_start: %u r_last_len: %u\n",
+             resv->r_start, ocfs2_resv_end(resv), resv->r_len,
+             resv->r_last_start, resv->r_last_len);
+
+        ocfs2_resv_insert(resmap, resv);
+}
+
+static void ocfs2_resv_find_window(struct ocfs2_reservation_map *resmap,
+                                   struct ocfs2_alloc_reservation *resv,
+                                   unsigned int wanted)
+{
+        unsigned int goal = 0;
+
+        BUG_ON(!ocfs2_resv_empty(resv));
+
+        /*
+         * Begin by trying to get a window as close to the previous
+         * one as possible. Using the most recent allocation as a
+         * start goal makes sense.
+         */
+        if (resv->r_last_len) {
+                goal = resv->r_last_start + resv->r_last_len;
+                if (goal >= resmap->m_bitmap_len)
+                        goal = 0;
+        }
+
+        __ocfs2_resv_find_window(resmap, resv, goal, wanted);
+
+        /* Search from last alloc didn't work, try once more from beginning. */
+        if (ocfs2_resv_empty(resv) && goal != 0)
+                __ocfs2_resv_find_window(resmap, resv, 0, wanted);
+
+        if (ocfs2_resv_empty(resv)) {
+                /*
+                 * Still empty? Pull oldest one off the LRU, remove it from
+                 * tree, put this one in it's place.
+                 */
+                ocfs2_cannibalize_resv(resmap, resv, wanted);
+        }
+
+        BUG_ON(ocfs2_resv_empty(resv));
+}
+
+int ocfs2_resmap_resv_bits(struct ocfs2_reservation_map *resmap,
+                           struct ocfs2_alloc_reservation *resv,
+                           int *cstart, int *clen)
+{
+        unsigned int wanted = *clen;
+
+        if (resv == NULL || ocfs2_resmap_disabled(resmap))
+                return -ENOSPC;
+
+        spin_lock(&resv_lock);
+
+        /*
+         * We don't want to over-allocate for temporary
+         * windows. Otherwise, we run the risk of fragmenting the
+         * allocation space.
+         */
+        wanted = ocfs2_resv_window_bits(resmap, resv);
+        if ((resv->r_flags & OCFS2_RESV_FLAG_TMP) || wanted < *clen)
+                wanted = *clen;
+
+        if (ocfs2_resv_empty(resv)) {
+                mlog(0, "empty reservation, find new window\n");
+
+                /*
+                 * Try to get a window here. If it works, we must fall
+                 * through and test the bitmap . This avoids some
+                 * ping-ponging of windows due to non-reserved space
+                 * being allocation before we initialize a window for
+                 * that inode.
+                 */
+                ocfs2_resv_find_window(resmap, resv, wanted);
+        }
+
+        BUG_ON(ocfs2_resv_empty(resv));
+
+        *cstart = resv->r_start;
+        *clen = resv->r_len;
+
+        spin_unlock(&resv_lock);
+        return 0;
+}
+
+static void
+        ocfs2_adjust_resv_from_alloc(struct ocfs2_reservation_map *resmap,
+                                     struct ocfs2_alloc_reservation *resv,
+                                     unsigned int start, unsigned int end)
+{
+        unsigned int lhs = 0, rhs = 0;
+
+        BUG_ON(start < resv->r_start);
+
+        /*
+         * Completely used? We can remove it then.
+         */
+        if (ocfs2_resv_end(resv) <= end && resv->r_start >= start) {
+                __ocfs2_resv_discard(resmap, resv);
+                return;
+        }
+
+        if (end < ocfs2_resv_end(resv))
+                rhs = end - ocfs2_resv_end(resv);
+
+        if (start > resv->r_start)
+                lhs = start - resv->r_start;
+
+        /*
+         * This should have been trapped above. At the very least, rhs
+         * should be non zero.
+         */
+        BUG_ON(rhs == 0 && lhs == 0);
+
+        if (rhs >= lhs) {
+                unsigned int old_end = ocfs2_resv_end(resv);
+
+                resv->r_start = end + 1;
+                resv->r_len = old_end - resv->r_start + 1;
+        } else {
+                resv->r_len = start - resv->r_start;
+        }
+}
+
+void ocfs2_resmap_claimed_bits(struct ocfs2_reservation_map *resmap,
+                               struct ocfs2_alloc_reservation *resv,
+                               u32 cstart, u32 clen)
+{
+        unsigned int cend = cstart + clen - 1;
+
+        if (resmap == NULL || ocfs2_resmap_disabled(resmap))
+                return;
+
+        if (resv == NULL)
+                return;
+
+        spin_lock(&resv_lock);
+
+        mlog(0, "claim bits: cstart: %u cend: %u clen: %u r_start: %u "
+             "r_end: %u r_len: %u, r_last_start: %u r_last_len: %u\n",
+             cstart, cend, clen, resv->r_start, ocfs2_resv_end(resv),
+             resv->r_len, resv->r_last_start, resv->r_last_len);
+
+        BUG_ON(cstart < resv->r_start);
+        BUG_ON(cstart > ocfs2_resv_end(resv));
+        BUG_ON(cend > ocfs2_resv_end(resv));
+
+        ocfs2_adjust_resv_from_alloc(resmap, resv, cstart, cend);
+        resv->r_last_start = cstart;
+        resv->r_last_len = clen;
+
+        /*
+         * May have been discarded above from
+         * ocfs2_adjust_resv_from_alloc().
+         */
+        if (!ocfs2_resv_empty(resv))
+                ocfs2_resv_mark_lru(resmap, resv);
+
+        mlog(0, "Reservation now looks like: r_start: %u r_end: %u "
+             "r_len: %u r_last_start: %u r_last_len: %u\n",
+             resv->r_start, ocfs2_resv_end(resv), resv->r_len,
+             resv->r_last_start, resv->r_last_len);
+
+        ocfs2_check_resmap(resmap);
+
+        spin_unlock(&resv_lock);
+}