ocfs2: Cache extent records

The extent map code was ripped out earlier because of an inability to deal
with holes. This patch adds back a simpler caching scheme requiring far less
code.

Our old extent map caching was designed back when meta data block caching in
Ocfs2 didn't work very well, resulting in many disk reads. These days our
metadata caching is much better, resulting in no un-necessary disk reads. As
a result, extent caching doesn't have to be as fancy, nor does it have to
cache as many extents. Keeping the last 3 extents seen should be sufficient
to give us a small performance boost on some streaming workloads.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>

1 files changed, 255 insertions, 0 deletions

diff --git a/fs/ocfs2/extent_map.c b/fs/ocfs2/extent_map.c
index f35e04f27f32..ba2b2ab1c6e4 100644
--- a/fs/ocfs2/extent_map.c
+++ b/fs/ocfs2/extent_map.c
@@ -39,6 +39,254 @@
 #include "buffer_head_io.h"
 
 /*
+ * The extent caching implementation is intentionally trivial.
+ *
+ * We only cache a small number of extents stored directly on the
+ * inode, so linear order operations are acceptable. If we ever want
+ * to increase the size of the extent map, then these algorithms must
+ * get smarter.
+ */
+
+void ocfs2_extent_map_init(struct inode *inode)
+{
+        struct ocfs2_inode_info *oi = OCFS2_I(inode);
+
+        oi->ip_extent_map.em_num_items = 0;
+        INIT_LIST_HEAD(&oi->ip_extent_map.em_list);
+}
+
+static void __ocfs2_extent_map_lookup(struct ocfs2_extent_map *em,
+                                      unsigned int cpos,
+                                      struct ocfs2_extent_map_item **ret_emi)
+{
+        unsigned int range;
+        struct ocfs2_extent_map_item *emi;
+
+        *ret_emi = NULL;
+
+        list_for_each_entry(emi, &em->em_list, ei_list) {
+                range = emi->ei_cpos + emi->ei_clusters;
+
+                if (cpos >= emi->ei_cpos && cpos < range) {
+                        list_move(&emi->ei_list, &em->em_list);
+
+                        *ret_emi = emi;
+                        break;
+                }
+        }
+}
+
+static int ocfs2_extent_map_lookup(struct inode *inode, unsigned int cpos,
+                                   unsigned int *phys, unsigned int *len,
+                                   unsigned int *flags)
+{
+        unsigned int coff;
+        struct ocfs2_inode_info *oi = OCFS2_I(inode);
+        struct ocfs2_extent_map_item *emi;
+
+        spin_lock(&oi->ip_lock);
+
+        __ocfs2_extent_map_lookup(&oi->ip_extent_map, cpos, &emi);
+        if (emi) {
+                coff = cpos - emi->ei_cpos;
+                *phys = emi->ei_phys + coff;
+                if (len)
+                        *len = emi->ei_clusters - coff;
+                if (flags)
+                        *flags = emi->ei_flags;
+        }
+
+        spin_unlock(&oi->ip_lock);
+
+        if (emi == NULL)
+                return -ENOENT;
+
+        return 0;
+}
+
+/*
+ * Forget about all clusters equal to or greater than cpos.
+ */
+void ocfs2_extent_map_trunc(struct inode *inode, unsigned int cpos)
+{
+        struct list_head *p, *n;
+        struct ocfs2_extent_map_item *emi;
+        struct ocfs2_inode_info *oi = OCFS2_I(inode);
+        struct ocfs2_extent_map *em = &oi->ip_extent_map;
+        LIST_HEAD(tmp_list);
+        unsigned int range;
+
+        spin_lock(&oi->ip_lock);
+        list_for_each_safe(p, n, &em->em_list) {
+                emi = list_entry(p, struct ocfs2_extent_map_item, ei_list);
+
+                if (emi->ei_cpos >= cpos) {
+                        /* Full truncate of this record. */
+                        list_move(&emi->ei_list, &tmp_list);
+                        BUG_ON(em->em_num_items == 0);
+                        em->em_num_items--;
+                        continue;
+                }
+
+                range = emi->ei_cpos + emi->ei_clusters;
+                if (range > cpos) {
+                        /* Partial truncate */
+                        emi->ei_clusters = cpos - emi->ei_cpos;
+                }
+        }
+        spin_unlock(&oi->ip_lock);
+
+        list_for_each_safe(p, n, &tmp_list) {
+                emi = list_entry(p, struct ocfs2_extent_map_item, ei_list);
+                list_del(&emi->ei_list);
+                kfree(emi);
+        }
+}
+
+/*
+ * Is any part of emi2 contained within emi1
+ */
+static int ocfs2_ei_is_contained(struct ocfs2_extent_map_item *emi1,
+                                 struct ocfs2_extent_map_item *emi2)
+{
+        unsigned int range1, range2;
+
+        /*
+         * Check if logical start of emi2 is inside emi1
+         */
+        range1 = emi1->ei_cpos + emi1->ei_clusters;
+        if (emi2->ei_cpos >= emi1->ei_cpos && emi2->ei_cpos < range1)
+                return 1;
+
+        /*
+         * Check if logical end of emi2 is inside emi1
+         */
+        range2 = emi2->ei_cpos + emi2->ei_clusters;
+        if (range2 > emi1->ei_cpos && range2 <= range1)
+                return 1;
+
+        return 0;
+}
+
+static void ocfs2_copy_emi_fields(struct ocfs2_extent_map_item *dest,
+                                  struct ocfs2_extent_map_item *src)
+{
+        dest->ei_cpos = src->ei_cpos;
+        dest->ei_phys = src->ei_phys;
+        dest->ei_clusters = src->ei_clusters;
+        dest->ei_flags = src->ei_flags;
+}
+
+/*
+ * Try to merge emi with ins. Returns 1 if merge succeeds, zero
+ * otherwise.
+ */
+static int ocfs2_try_to_merge_extent_map(struct ocfs2_extent_map_item *emi,
+                                         struct ocfs2_extent_map_item *ins)
+{
+        /*
+         * Handle contiguousness
+         */
+        if (ins->ei_phys == (emi->ei_phys + emi->ei_clusters) &&
+            ins->ei_cpos == (emi->ei_cpos + emi->ei_clusters) &&
+            ins->ei_flags == emi->ei_flags) {
+                emi->ei_clusters += ins->ei_clusters;
+                return 1;
+        } else if ((ins->ei_phys + ins->ei_clusters) == emi->ei_phys &&
+                   (ins->ei_cpos + ins->ei_clusters) == emi->ei_phys &&
+                   ins->ei_flags == emi->ei_flags) {
+                emi->ei_phys = ins->ei_phys;
+                emi->ei_cpos = ins->ei_cpos;
+                emi->ei_clusters += ins->ei_clusters;
+                return 1;
+        }
+
+        /*
+         * Overlapping extents - this shouldn't happen unless we've
+         * split an extent to change it's flags. That is exceedingly
+         * rare, so there's no sense in trying to optimize it yet.
+         */
+        if (ocfs2_ei_is_contained(emi, ins) ||
+            ocfs2_ei_is_contained(ins, emi)) {
+                ocfs2_copy_emi_fields(emi, ins);
+                return 1;
+        }
+
+        /* No merge was possible. */
+        return 0;
+}
+
+/*
+ * In order to reduce complexity on the caller, this insert function
+ * is intentionally liberal in what it will accept.
+ *
+ * The only rule is that the truncate call *must* be used whenever
+ * records have been deleted. This avoids inserting overlapping
+ * records with different physical mappings.
+ */
+void ocfs2_extent_map_insert_rec(struct inode *inode,
+                                 struct ocfs2_extent_rec *rec)
+{
+        struct ocfs2_inode_info *oi = OCFS2_I(inode);
+        struct ocfs2_extent_map *em = &oi->ip_extent_map;
+        struct ocfs2_extent_map_item *emi, *new_emi = NULL;
+        struct ocfs2_extent_map_item ins;
+
+        ins.ei_cpos = le32_to_cpu(rec->e_cpos);
+        ins.ei_phys = ocfs2_blocks_to_clusters(inode->i_sb,
+                                               le64_to_cpu(rec->e_blkno));
+        ins.ei_clusters = le16_to_cpu(rec->e_leaf_clusters);
+        ins.ei_flags = rec->e_flags;
+
+search:
+        spin_lock(&oi->ip_lock);
+
+        list_for_each_entry(emi, &em->em_list, ei_list) {
+                if (ocfs2_try_to_merge_extent_map(emi, &ins)) {
+                        list_move(&emi->ei_list, &em->em_list);
+                        spin_unlock(&oi->ip_lock);
+                        goto out;
+                }
+        }
+
+        /*
+         * No item could be merged.
+         *
+         * Either allocate and add a new item, or overwrite the last recently
+         * inserted.
+         */
+
+        if (em->em_num_items < OCFS2_MAX_EXTENT_MAP_ITEMS) {
+                if (new_emi == NULL) {
+                        spin_unlock(&oi->ip_lock);
+
+                        new_emi = kmalloc(sizeof(*new_emi), GFP_NOFS);
+                        if (new_emi == NULL)
+                                goto out;
+
+                        goto search;
+                }
+
+                ocfs2_copy_emi_fields(new_emi, &ins);
+                list_add(&new_emi->ei_list, &em->em_list);
+                em->em_num_items++;
+                new_emi = NULL;
+        } else {
+                BUG_ON(list_empty(&em->em_list) || em->em_num_items == 0);
+                emi = list_entry(em->em_list.prev,
+                                 struct ocfs2_extent_map_item, ei_list);
+                list_move(&emi->ei_list, &em->em_list);
+                ocfs2_copy_emi_fields(emi, &ins);
+        }
+
+        spin_unlock(&oi->ip_lock);
+
+out:
+        if (new_emi)
+                kfree(new_emi);
+}
+
+/*
  * Return the 1st index within el which contains an extent start
  * larger than v_cluster.
  */
@@ -174,6 +422,11 @@ int ocfs2_get_clusters(struct inode *inode, u32 v_cluster,
         struct ocfs2_extent_rec *rec;
         u32 coff;
 
+        ret = ocfs2_extent_map_lookup(inode, v_cluster, p_cluster,
+                                      num_clusters, extent_flags);
+        if (ret == 0)
+                goto out;
+
         ret = ocfs2_read_block(OCFS2_SB(inode->i_sb), OCFS2_I(inode)->ip_blkno,
                                &di_bh, OCFS2_BH_CACHED, inode);
         if (ret) {
@@ -245,6 +498,8 @@ int ocfs2_get_clusters(struct inode *inode, u32 v_cluster,
                         *num_clusters = ocfs2_rec_clusters(el, rec) - coff;
 
                 flags = rec->e_flags;
+
+                ocfs2_extent_map_insert_rec(inode, rec);
         }
 
         if (extent_flags)