[PATCH RFC 4/5] ext4: Prepare ext4_mb_discard_preallocations() for handling EXT4_MB_HINT_GOAL_ONLY

[Kirill Tkhai <ktkhai@virtuozzo.com>]

EXT4_MB_HINT_GOAL_ONLY is currently unused. This patch teaches
ext4_mb_discard_preallocations() to discard only that preallocated
range, which contains a specified block, in case of the flag is set.
Otherwise, a preallocated range is not discarded.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
---
 fs/ext4/mballoc.c |   28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 51a78eb65f3c..b1b3c5526d1a 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -3894,8 +3894,8 @@ ext4_mb_release_group_pa(struct ext4_buddy *e4b,
  *   1) how many requested
  */
 static noinline_for_stack int
-ext4_mb_discard_group_preallocations(struct super_block *sb,
-					ext4_group_t group, int needed)
+ext4_mb_discard_group_preallocations(struct super_block *sb, ext4_group_t group,
+				     int needed, ext4_fsblk_t goal)
 {
 	struct ext4_group_info *grp = ext4_get_group_info(sb, group);
 	struct buffer_head *bitmap_bh = NULL;
@@ -3947,6 +3947,12 @@ ext4_mb_discard_group_preallocations(struct super_block *sb,
 			continue;
 		}
 
+		if (goal != (ext4_fsblk_t)-1 &&
+		    (goal < pa->pa_pstart || goal >= pa->pa_pstart + pa->pa_len)) {
+			spin_unlock(&pa->pa_lock);
+			continue;
+		}
+
 		/* seems this one can be freed ... */
 		pa->pa_deleted = 1;
 
@@ -4462,15 +4468,23 @@ static int ext4_mb_release_context(struct ext4_allocation_context *ac)
 	return 0;
 }
 
-static int ext4_mb_discard_preallocations(struct super_block *sb, int needed)
+static int ext4_mb_discard_preallocations(struct super_block *sb,
+					  struct ext4_allocation_context *ac)
 {
-	ext4_group_t i, ngroups = ext4_get_groups_count(sb);
+	ext4_group_t i = 0, ngroups = ext4_get_groups_count(sb);
+	int needed = ac->ac_o_ex.fe_len;
+	ext4_fsblk_t goal = (ext4_fsblk_t)-1;
 	int ret;
 	int freed = 0;
 
+	if (ac->ac_flags & EXT4_MB_HINT_GOAL_ONLY) {
+		i = ac->ac_o_ex.fe_group;
+		ngroups = i + 1;
+		goal = ext4_grp_offs_to_block(ac->ac_sb, &ac->ac_g_ex);
+	}
 	trace_ext4_mb_discard_preallocations(sb, needed);
-	for (i = 0; i < ngroups && needed > 0; i++) {
-		ret = ext4_mb_discard_group_preallocations(sb, i, needed);
+	for (; i < ngroups && needed > 0; i++) {
+		ret = ext4_mb_discard_group_preallocations(sb, i, needed, goal);
 		freed += ret;
 		needed -= ret;
 	}
@@ -4585,7 +4599,7 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
 			ar->len = ac->ac_b_ex.fe_len;
 		}
 	} else {
-		freed  = ext4_mb_discard_preallocations(sb, ac->ac_o_ex.fe_len);
+		freed  = ext4_mb_discard_preallocations(sb, ac);
 		if (freed)
 			goto repeat;
 		*errp = -ENOSPC;