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md: Removal of hash table in linear raid

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Get rid of sector_div and hash table for linear raid and replace
with a linear search in which_dev.
The hash table adds a lot of complexity for little if any gain.
Ultimately a binary search will be used which will have smaller
cache foot print, a similar number of memory access, and no
divisions.

Signed-off-by: Sandeep K Sinha <sandeepksinha@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>
This commit is contained in:
Sandeep K Sinha 2009-06-16 16:55:26 +10:00 committed by NeilBrown
parent 070ec55d07
commit 45d4582f21
2 changed files with 3 additions and 95 deletions
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93
drivers/md/linear.c
View file

@ -29,13 +29,8 @@ static inline dev_info_t *which_dev(mddev_t *mddev, sector_t sector)
{
dev_info_t *hash;
linear_conf_t *conf = mddev->private;
sector_t idx = sector >> conf->sector_shift;
/*
* sector_div(a,b) returns the remainer and sets a to a/b
*/
(void)sector_div(idx, conf->spacing);
hash = conf->hash_table[idx];
hash = conf->disks;
while (sector >= hash->num_sectors + hash->start_sector)
hash++;
@ -114,11 +109,8 @@ static sector_t linear_size(mddev_t *mddev, sector_t sectors, int raid_disks)
static linear_conf_t *linear_conf(mddev_t *mddev, int raid_disks)
{
linear_conf_t *conf;
dev_info_t **table;
mdk_rdev_t *rdev;
int i, nb_zone, cnt;
sector_t min_sectors;
sector_t curr_sector;
int i, cnt;
conf = kzalloc (sizeof (*conf) + raid_disks*sizeof(dev_info_t),
GFP_KERNEL);
@ -159,63 +151,8 @@ static linear_conf_t *linear_conf(mddev_t *mddev, int raid_disks)
goto out;
}
min_sectors = conf->array_sectors;
sector_div(min_sectors, PAGE_SIZE/sizeof(struct dev_info *));
if (min_sectors == 0)
min_sectors = 1;
/* min_sectors is the minimum spacing that will fit the hash
* table in one PAGE. This may be much smaller than needed.
* We find the smallest non-terminal set of consecutive devices
* that is larger than min_sectors and use the size of that as
* the actual spacing
*/
conf->spacing = conf->array_sectors;
for (i=0; i < cnt-1 ; i++) {
sector_t tmp = 0;
int j;
for (j = i; j < cnt - 1 && tmp < min_sectors; j++)
tmp += conf->disks[j].num_sectors;
if (tmp >= min_sectors && tmp < conf->spacing)
conf->spacing = tmp;
}
/* spacing may be too large for sector_div to work with,
* so we might need to pre-shift
*/
conf->sector_shift = 0;
if (sizeof(sector_t) > sizeof(u32)) {
sector_t space = conf->spacing;
while (space > (sector_t)(~(u32)0)) {
space >>= 1;
conf->sector_shift++;
}
}
/*
* This code was restructured to work around a gcc-2.95.3 internal
* compiler error. Alter it with care.
*/
{
sector_t sz;
unsigned round;
unsigned long base;
sz = conf->array_sectors >> conf->sector_shift;
sz += 1; /* force round-up */
base = conf->spacing >> conf->sector_shift;
round = sector_div(sz, base);
nb_zone = sz + (round ? 1 : 0);
}
BUG_ON(nb_zone > PAGE_SIZE / sizeof(struct dev_info *));
conf->hash_table = kmalloc (sizeof (struct dev_info *) * nb_zone,
GFP_KERNEL);
if (!conf->hash_table)
goto out;
/*
* Here we generate the linear hash table
* First calculate the device offsets.
* Here we calculate the device offsets.
*/
conf->disks[0].start_sector = 0;
for (i = 1; i < raid_disks; i++)
@ -223,29 +160,6 @@ static linear_conf_t *linear_conf(mddev_t *mddev, int raid_disks)
conf->disks[i-1].start_sector +
conf->disks[i-1].num_sectors;
table = conf->hash_table;
i = 0;
for (curr_sector = 0;
curr_sector < conf->array_sectors;
curr_sector += conf->spacing) {
while (i < raid_disks-1 &&
curr_sector >= conf->disks[i+1].start_sector)
i++;
*table ++ = conf->disks + i;
}
if (conf->sector_shift) {
conf->spacing >>= conf->sector_shift;
/* round spacing up so that when we divide by it,
* we err on the side of "too-low", which is safest.
*/
conf->spacing++;
}
BUG_ON(table - conf->hash_table > nb_zone);
return conf;
out:
@ -309,7 +223,6 @@ static int linear_stop (mddev_t *mddev)
blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
do {
linear_conf_t *t = conf->prev;
kfree(conf->hash_table);
kfree(conf);
conf = t;
} while (conf);

5
drivers/md/linear.h
View file

@ -12,12 +12,7 @@ typedef struct dev_info dev_info_t;
struct linear_private_data
{
struct linear_private_data *prev; /* earlier version */
dev_info_t **hash_table;
sector_t spacing;
sector_t array_sectors;
int sector_shift; /* shift before dividing
* by spacing
*/
dev_info_t disks[0];
};