Re: Found a new bug!

[djani22@dynamicweb.hu]

Thanks, I will test it, when I can...

In this moment, my system is an working online system, and now only one 8TB
space what I can use...
Thats right, maybe I can built linear array from only one soure device,but:
My first problem is, on my 8TB device is already exists XFS filesystem, with
valuable data, what I can't backup.
It is still OK, but I can't insert one raid layer, because the raid's
superblock, and the XFS is'nt shrinkable. :-(

The only one way (I think) to plug in another raw device, and build an array
from 8TB-device + new small device, to get much space to FS.

But it is too risky for me!

Do you think it is safe?

Currently I use 2.6.13-rc3.
This patch is good for this version, or only the last version?

Witch is the last? 2.6.13-rc6 or rc6-git7, or 2.6.14 -git cvs? :)

Thanks,

Janos


----- Original Message -----
From: "Neil Brown" <neilb@cse.unsw.edu.au>
To: <djani22@dynamicweb.hu>
Cc: <linux-raid@vger.kernel.org>
Sent: Monday, August 15, 2005 3:21 AM
Subject: Re: Found a new bug!


> On Monday August 15, djani22@dynamicweb.hu wrote:
> > Hello list, Neil!
> >
> > Is there something news with the 2TB raid-input problem?
> > Sooner or later, I will need to join two 8TB array to one big 16TB. :-)
>
> Thanks for the reminder.
>
> The following patch should work, but my test machine won't boot the
> current -mm kernels :-( so it is hard to test properly.
>
> Let me know the results if you are able to test it.
>
> Thanks,
> NeilBrown
>
> ---------------------------------
> Support md/linear array with components greater than 2 terabytes.
>
> linear currently uses division by the size of the smallest componenet
> device to find which device a request goes to.
> If that smallest device is larger than 2 terabytes, then the division
> will not work on some systems.
>
> So we introduce a pre-shift, and take care not to make the hash table
> too large, much like the code in raid0.
>
> Also get rid of conf->nr_zones, which is not needed.
>
> Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
>
> ### Diffstat output
>  ./drivers/md/linear.c         |   99
++++++++++++++++++++++++++++--------------
>  ./include/linux/raid/linear.h |    4 -
>  2 files changed, 70 insertions(+), 33 deletions(-)
>
> diff ./drivers/md/linear.c~current~ ./drivers/md/linear.c
> --- ./drivers/md/linear.c~current~ 2005-08-15 11:18:21.000000000 +1000
> +++ ./drivers/md/linear.c 2005-08-15 11:18:27.000000000 +1000
> @@ -38,7 +38,8 @@ static inline dev_info_t *which_dev(mdde
>   /*
>   * sector_div(a,b) returns the remainer and sets a to a/b
>   */
> - (void)sector_div(block, conf->smallest->size);
> + block >>= conf->preshift;
> + (void)sector_div(block, conf->hash_spacing);
>   hash = conf->hash_table[block];
>
>   while ((sector>>1) >= (hash->size + hash->offset))
> @@ -47,7 +48,7 @@ static inline dev_info_t *which_dev(mdde
>  }
>
>  /**
> - * linear_mergeable_bvec -- tell bio layer if a two requests can be
merged
> + * linear_mergeable_bvec -- tell bio layer if two requests can be merged
>   * @q: request queue
>   * @bio: the buffer head that's been built up so far
>   * @biovec: the request that could be merged to it.
> @@ -116,7 +117,7 @@ static int linear_run (mddev_t *mddev)
>   dev_info_t **table;
>   mdk_rdev_t *rdev;
>   int i, nb_zone, cnt;
> - sector_t start;
> + sector_t min_spacing;
>   sector_t curr_offset;
>   struct list_head *tmp;
>
> @@ -127,11 +128,6 @@ static int linear_run (mddev_t *mddev)
>   memset(conf, 0, sizeof(*conf) + mddev->raid_disks*sizeof(dev_info_t));
>   mddev->private = conf;
>
> - /*
> - * Find the smallest device.
> - */
> -
> - conf->smallest = NULL;
>   cnt = 0;
>   mddev->array_size = 0;
>
> @@ -159,8 +155,6 @@ static int linear_run (mddev_t *mddev)
>   disk->size = rdev->size;
>   mddev->array_size += rdev->size;
>
> - if (!conf->smallest || (disk->size < conf->smallest->size))
> - conf->smallest = disk;
>   cnt++;
>   }
>   if (cnt != mddev->raid_disks) {
> @@ -168,6 +162,36 @@ static int linear_run (mddev_t *mddev)
>   goto out;
>   }
>
> + min_spacing = mddev->array_size;
> + sector_div(min_spacing, PAGE_SIZE/sizeof(struct dev_info *));
> +
> + /* min_spacing 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_spacing as use the size of that as
> + * the actual spacing
> + */
> + conf->hash_spacing = mddev->array_size;
> + for (i=0; i < cnt-1 ; i++) {
> + sector_t sz = 0;
> + int j;
> + for (j=i; i<cnt-1 && sz < min_spacing ; j++)
> + sz += conf->disks[j].size;
> + if (sz >= min_spacing && sz < conf->hash_spacing)
> + conf->hash_spacing = sz;
> + }
> +
> + /* hash_spacing may be too large for sector_div to work with,
> + * so we might need to pre-shift
> + */
> + conf->preshift = 0;
> + if (sizeof(sector_t) > sizeof(u32)) {
> + sector_t space = conf->hash_spacing;
> + while (space > (sector_t)(~(u32)0)) {
> + space >>= 1;
> + conf->preshift++;
> + }
> + }
>   /*
>   * This code was restructured to work around a gcc-2.95.3 internal
>   * compiler error.  Alter it with care.
> @@ -177,39 +201,52 @@ static int linear_run (mddev_t *mddev)
>   unsigned round;
>   unsigned long base;
>
> - sz = mddev->array_size;
> - base = conf->smallest->size;
> + sz = mddev->array_size >> conf->preshift;
> + sz += 1; /* force round-up */
> + base = conf->hash_spacing >> conf->preshift;
>   round = sector_div(sz, base);
> - nb_zone = conf->nr_zones = sz + (round ? 1 : 0);
> + nb_zone = sz + (round ? 1 : 0);
>   }
> -
> - conf->hash_table = kmalloc (sizeof (dev_info_t*) * nb_zone,
> + 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.
>   */
> + conf->disks[0].offset = 0;
> + for (i=1; i<mddev->raid_disks; i++)
> + conf->disks[i].offset =
> + conf->disks[i-1].offset +
> + conf->disks[i-1].size;
> +
>   table = conf->hash_table;
> - start = 0;
>   curr_offset = 0;
> - for (i = 0; i < cnt; i++) {
> - dev_info_t *disk = conf->disks + i;
> -
> - disk->offset = curr_offset;
> - curr_offset += disk->size;
> -
> - /* 'curr_offset' is the end of this disk
> - * 'start' is the start of table
> + i = 0;
> + for (curr_offset = 0;
> +      curr_offset < mddev->array_size;
> +      curr_offset += conf->hash_spacing) {
> +
> + while (i < mddev->raid_disks-1 &&
> +        curr_offset >= conf->disks[i+1].offset)
> + i++;
> +
> + *table ++ = conf->disks + i;
> + }
> +
> + if (conf->preshift) {
> + conf->hash_spacing >>= conf->preshift;
> + /* round hash_spacing up so that when we divide by it,
> + * we err on the side of "too-low", which is safest.
>   */
> - while (start < curr_offset) {
> - *table++ = disk;
> - start += conf->smallest->size;
> - }
> + conf->hash_spacing++;
>   }
> - if (table-conf->hash_table != nb_zone)
> - BUG();
> +
> + BUG_ON(table - conf->hash_table > nb_zone);
>
>   blk_queue_merge_bvec(mddev->queue, linear_mergeable_bvec);
>   mddev->queue->unplug_fn = linear_unplug;
> @@ -299,7 +336,7 @@ static void linear_status (struct seq_fi
>   sector_t s = 0;
>
>   seq_printf(seq, "      ");
> - for (j = 0; j < conf->nr_zones; j++)
> + for (j = 0; j < mddev->raid_disks; j++)
>   {
>   char b[BDEVNAME_SIZE];
>   s += conf->smallest_size;
>
> diff ./include/linux/raid/linear.h~current~ ./include/linux/raid/linear.h
> --- ./include/linux/raid/linear.h~current~ 2005-08-15 11:18:21.000000000
+1000
> +++ ./include/linux/raid/linear.h 2005-08-15 09:13:55.000000000 +1000
> @@ -14,8 +14,8 @@ typedef struct dev_info dev_info_t;
>  struct linear_private_data
>  {
>   dev_info_t **hash_table;
> - dev_info_t *smallest;
> - int nr_zones;
> + sector_t hash_spacing;
> + int preshift; /* shift before dividing by hash_spacing */
>   dev_info_t disks[0];
>  };
>
> -
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