Hi Ted, Andreas and the list,
After the bigalloc-feature is completed in ext4, we could have much
more big size of block-group (also bigger continuous space), so larger
extent size which is above 128MB is necessary, such as:
struct ext4_extent_large {
__le64 ee_block; /* first logical block extent covers */
__le64 ee_start; /* starting physical block */
__le32 ee_len; /* number of blocks covered by extent */
__le32 ee_flags; /* flags and future extension */
};
On the other hand, people who use ext4 in desktop environment may need
more compact format like:
struct ext4_extent_packed {
__le32 ee_start_lo;
__le16 ee_start_hi;
__le16 ee_len;
};
which they can fit 6 extents in the inode.
Therefore, supporting multiple extent formats is the solution which
satisfied both.
My Plan:
First, abstracting the operation on disk extent format out:
struct ext4_ext_operation {
__u16 (*ext_size) (void);
/* the size of struct ext4_extent_### */
ext4_fsblk_t (*ext_pblock) (void *extent);
void (*ext_store_pblock) (void *extent, __u64 pb);
ext4_lblk_t (*ext_lblock) (void *extent);
ext4_lblk_t (*ext_len) (void *extent);
int (*is_uninit) (void *extent);
void (*mark_uninit) (void *extent);
void (*mark_init) (void *extent);
__u16 (*idx_size) (void);
ext4_fsblk_t (*idx_pblock) (void *idx);
void (*idx_store_pblock) (void *idx, __u64 pb);
ext4_lblk_t (*idx_lblock) (void *idx);
};
We can use this single entry to handle different extent format through
different implementation of ext4_ext_operation (choosing different
implementation by different eh_magic number),
and the extent format which is used now could be implemented like:
static const struct ext4_ext_operation ext4_normal_eops= {
.ext_size = ext4_ext_size,
.ext_pblock = ext4_ext_pblock,
.ext_store_pblock = ext4_ext_store_pblock,
.ext_lblock = ext4_ext_lblock,
.ext_len = ext4_ext_get_actual_len,
.is_uninit = ext4_ext_is_uninitialized,
.mark_uninit = ext4_ext_mark_uninitialized,
.mark_init = ext4_ext_mark_initialized,
.idx_size = ext4_idx_size,
.idx_pblock = ext4_idx_pblock,
.idx_store_pblock = ext4_idx_store_pblock,
.idx_lblock = ext4_idx_lblock,
};
For instance, the function ext4_ext_binsearch_idx() may look like:
static void ext4_ext_binsearch_idx(struct inode *inode,
struct ext4_ext_path *path, ext4_lblk_t block)
{
struct ext4_extent_header *eh = path->p_hdr;
struct void *r, *l, *m;
struct ext4_ext_operation *op = (struct
ext4_ext_operation*)inode->private;
l = (char *) (eh) + sizeof(struct ext4_extent_header) +
op->idx_size();
r = l + (le16_to_cpu(eh)->eh_entries) * op->idx_size();
while (l <= r) {
m = l + op->idx_size() * ((r - l) / op->idx_size())/
2;
if (block < op->idx_lblock(m))
r = m - op->idx_size();
else
l = m + op->idx_size();
}
path->p_idx = l - op->idx_size();
}
The only problem is the performance regression caused by frequent
function calls.
Any suggestions will be appreciated.
--
--
Best Regard
Robin Dong
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