From: Sandeep K Sinha Date: Tue, 16 Jun 2009 06:55:26 +0000 (+1000) Subject: md: Removal of hash table in linear raid X-Git-Tag: v2.6.31-rc1~143^2~27 X-Git-Url: http://ftp.safe.ca/?a=commitdiff_plain;h=45d4582f219619e368ea91ea1189085e1c5f1969;p=safe%2Fjmp%2Flinux-2.6 md: Removal of hash table in linear raid 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 Signed-off-by: NeilBrown --- diff --git a/drivers/md/linear.c b/drivers/md/linear.c index 31f8ec7..92bcd3d 100644 --- a/drivers/md/linear.c +++ b/drivers/md/linear.c @@ -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); diff --git a/drivers/md/linear.h b/drivers/md/linear.h index 76078f1..721a878 100644 --- a/drivers/md/linear.h +++ b/drivers/md/linear.h @@ -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]; };