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super1: leave more space in front of data by default. 

The kernel is growing the ability to avoid the need for a
backup file during reshape by being able to change the data offset.

For this to be useful we need plenty of free space before the
data so the data offset can be reduced.

So for v1.1 and v1.2 metadata make the default data_offset much
larger.  Aim for 128Meg, but keep a power of 2 and don't use more
than 0.1% of each device.

Don't change v1.0 as that is used when the data_offset is required to
be zero.

Signed-off-by: NeilBrown <neilb@suse.de>
This commit is contained in:
NeilBrown 2012-04-04 14:00:40 +10:00
parent fbdef49811
commit 508a7f16b2
1 changed files with 21 additions and 6 deletions
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27
super1.c
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@ -1094,7 +1094,7 @@ static int write_init_super1(struct supertype *st)
unsigned long long reserved;
struct devinfo *di;
unsigned long long dsize, array_size;
unsigned long long sb_offset;
unsigned long long sb_offset, headroom;
for (di = st->info; di && ! rv ; di = di->next) {
if (di->disk.state == 1)
@ -1167,6 +1167,14 @@ static int write_init_super1(struct supertype *st)
/* work out how much space we left for a bitmap */
bm_space = choose_bm_space(array_size);
/* We try to leave 0.1% at the start for reshape
* operations, but limit this to 128Meg (0.1% of 10Gig)
* which is plenty for efficient reshapes
*/
headroom = 128 * 1024 * 2;
while (headroom << 10 > array_size)
headroom >>= 1;
switch(st->minor_version) {
case 0:
sb_offset = dsize;
@ -1189,6 +1197,9 @@ static int write_init_super1(struct supertype *st)
/* force 4K alignment */
reserved &= ~7ULL;
if (reserved < headroom)
reserved = headroom;
sb->data_offset = __cpu_to_le64(reserved);
sb->data_size = __cpu_to_le64(dsize - reserved);
break;
@ -1209,6 +1220,9 @@ static int write_init_super1(struct supertype *st)
/* force 4K alignment */
reserved &= ~7ULL;
if (reserved < headroom)
reserved = headroom;
sb->data_offset = __cpu_to_le64(reserved);
sb->data_size = __cpu_to_le64(dsize - reserved);
break;
@ -1506,12 +1520,13 @@ static __u64 avail_size1(struct supertype *st, __u64 devsize)
st->minor_version = 2;
if (super == NULL && st->minor_version > 0) {
/* haven't committed to a size yet, so allow some
* slack for alignment of data_offset.
* We haven't access to device details so allow
* 1 Meg if bigger than 1Gig
* slack for space for reshape.
* Limit slack to 128M, but aim for about 0.1%
*/
if (devsize > 1024*1024*2)
devsize -= 1024*2;
unsigned long long headroom = 128*1024*2;
while ((headroom << 10) > devsize)
headroom >>= 1;
devsize -= headroom;
}
switch(st->minor_version) {
case 0: