ext4: delalloc --estimate need metadata blocks to reserve
From: Mingming cao <cmm@xxxxxxxxxx>
Calculate the number of metadata blocks needed to allocate blocks
Worse case is one block per extent
Signed-off-by: Mingming cao <cmm@xxxxxxxxxx>
---
fs/ext4/ext4_extents.h | 1 +
fs/ext4/extents.c | 30 ++++++++++++++++++++++++++++++
2 files changed, 31 insertions(+)
Index: linux-2.6.26-rc4/fs/ext4/ext4_extents.h
===================================================================
--- linux-2.6.26-rc4.orig/fs/ext4/ext4_extents.h 2008-06-01 14:22:03.000000000 -0700
+++ linux-2.6.26-rc4/fs/ext4/ext4_extents.h 2008-06-01 14:57:57.000000000 -0700
@@ -212,6 +212,7 @@ static inline int ext4_ext_get_actual_le
(le16_to_cpu(ext->ee_len) - EXT_INIT_MAX_LEN));
}
+extern int ext4_ext_calc_metadata_amount(struct inode *inode, int blocks);
extern ext4_fsblk_t idx_pblock(struct ext4_extent_idx *);
extern void ext4_ext_store_pblock(struct ext4_extent *, ext4_fsblk_t);
extern int ext4_extent_tree_init(handle_t *, struct inode *);
Index: linux-2.6.26-rc4/fs/ext4/extents.c
===================================================================
--- linux-2.6.26-rc4.orig/fs/ext4/extents.c 2008-06-01 14:22:03.000000000 -0700
+++ linux-2.6.26-rc4/fs/ext4/extents.c 2008-06-01 14:57:57.000000000 -0700
@@ -246,6 +246,36 @@ static int ext4_ext_space_root_idx(struc
return size;
}
+/*
+ * Calculate the number of metadata blocks needed
+ * to allocate @blocks
+ * Worse case is one block per extent
+ */
+int ext4_ext_calc_metadata_amount(struct inode *inode, int blocks)
+{
+ int lcap, icap, rcap, leafs, idxs, num;
+ int newextents = blocks;
+
+ rcap = ext4_ext_space_root_idx(inode);
+ lcap = ext4_ext_space_block(inode);
+ icap = ext4_ext_space_block_idx(inode);
+
+ /* number of new leaf blocks needed */
+ num = leafs = (newextents + lcap - 1) / lcap;
+
+ /*
+ * Worse case, we need separate index block(s)
+ * to link all new leaf blocks
+ */
+ idxs = (leafs + icap - 1) / icap;
+ do {
+ num += idxs;
+ idxs = (idxs + icap - 1) / icap;
+ } while (idxs > rcap);
+
+ return num;
+}
+
static int
ext4_ext_max_entries(struct inode *inode, int depth)
{
--
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