lots and lots of disks again

Andrew Morton
2004-02-04T10:43:36Z

You can't hide from me you know ;)

What to do about this?

Last time it was discussed we had:

Christoph Hellwig <hch@infradead.org> wrote:
>
>
> - I think the bitmap overhead was killing us on big x86 machines, right?
> so that might need some swork.
> - a config option definitly is the wrong way to go.
> - I don't think assigning more numbers to the last major is a bad idea,
> better assign them to the first one, maybe with a hole for what we're
> using the other majors currently for, so when udev gets more mature
> we can kill the additional majors.

Matthew Wilcox <willy@debian.org> wrote:
>
> LWN were kind enough to archive my previous thoughts on this at
> http://lwn.net/Articles/54840/
>
> I'd've worked on some code for this if anyone had been interested ...

badari <pbadari@us.ibm.com> wrote:
>
> I am not sorry for not replying for so long. I have been on vacation.
>
> 1) I am not really concerned about bitmap overhead. Bitmap of one
> page (4k) - should be enough to support 32K disks. That should be
> good enough for most of the machines.
>
> 2) I used config option for 2 reasons
> - to minimize impact on machines this is not needed.
> - didn't want to depend on <major, minor> split to decide on
> how many disks we can support.
>
> 3) The reason, I assigned all the disks to last major is to maintain backward
> compatibility with current major, minor assignments. Hopefully "udev"
> will cleanup all these.
>
> My question is, what do we do for current 2.6 ? Hoping to address these
> before distros start making 2.6 distros and adding their own stuff to support
> this.
>
> And also, is there a plan to support more partitions per disk ?

And nothing happened.

From: Badari Pulavarty <pbadari@us.ibm.com>

Here is the patch to support large number of SCSI disks. The patch is not
fully cooked yet. I was hoping to use this generate discussion. I have
not tested it fully on 2.6.0-test6-mm1.

As I mentioned earlier, it maintains backward compatibility with existing
sd major/minors - by attached all the new disks to last sd major. And
also, I made the number of disks to support as configurable - to avoid
dependency on how many minor bits.

---

drivers/scsi/Kconfig | 8 ++++++++
drivers/scsi/sd.c | 25 +++++++++++++++++++------
2 files changed, 27 insertions(+), 6 deletions(-)

diff -puN drivers/scsi/Kconfig~support-zillions-of-scsi-disks drivers/scsi/Kconfig
--- 25/drivers/scsi/Kconfig~support-zillions-of-scsi-disks 2004-01-07 19:10:47.000000000 -0800
+++ 25-akpm/drivers/scsi/Kconfig 2004-01-07 19:10:47.000000000 -0800
@@ -55,6 +55,14 @@ config BLK_DEV_SD
In this case, do not compile the driver for your SCSI host adapter
(below) as a module either.

+config MAX_SD_DISKS
+ int "Maximum number of SCSI disks to support (256-8192)"
+ depends on BLK_DEV_SD
+ default "256"
+ help
+ The maximum number SCSI disks to support. Default is 256.
+ Change this value if you want kernel to support lots of SCSI devices.
+
config CHR_DEV_ST
tristate "SCSI tape support"
depends on SCSI
diff -puN drivers/scsi/sd.c~support-zillions-of-scsi-disks drivers/scsi/sd.c
--- 25/drivers/scsi/sd.c~support-zillions-of-scsi-disks 2004-01-07 19:10:47.000000000 -0800
+++ 25-akpm/drivers/scsi/sd.c 2004-01-07 19:10:47.000000000 -0800
@@ -62,6 +62,7 @@
*/
#define SD_MAJORS 16
#define SD_DISKS (SD_MAJORS << 4)
+#define TOTAL_SD_DISKS CONFIG_MAX_SD_DISKS

/*
* Time out in seconds for disks and Magneto-opticals (which are slower).
@@ -95,7 +96,7 @@ struct scsi_disk {
};

-static unsigned long sd_index_bits[SD_DISKS / BITS_PER_LONG];
+static unsigned long sd_index_bits[TOTAL_SD_DISKS / BITS_PER_LONG];
static spinlock_t sd_index_lock = SPIN_LOCK_UNLOCKED;

static int sd_revalidate_disk(struct gendisk *disk);
@@ -130,6 +131,9 @@ static int sd_major(int major_idx)
return SCSI_DISK1_MAJOR + major_idx - 1;
case 8 ... 15:
return SCSI_DISK8_MAJOR + major_idx - 8;
+#define MAX_IDX (TOTAL_SD_DISKS >> 4)
+ case 16 ... MAX_IDX:
+ return SCSI_DISK15_MAJOR;
default:
BUG();
return 0; /* shut up gcc */
@@ -1320,8 +1324,8 @@ static int sd_probe(struct device *dev)
goto out_free;

spin_lock(&sd_index_lock);
- index = find_first_zero_bit(sd_index_bits, SD_DISKS);
- if (index == SD_DISKS) {
+ index = find_first_zero_bit(sd_index_bits, TOTAL_SD_DISKS);
+ if (index == TOTAL_SD_DISKS) {
spin_unlock(&sd_index_lock);
error = -EBUSY;
goto out_put;
@@ -1336,15 +1340,24 @@ static int sd_probe(struct device *dev)
sdkp->openers = 0;

gd->major = sd_major(index >> 4);
- gd->first_minor = (index & 15) << 4;
+ if (index > SD_DISKS)
+ gd->first_minor = ((index - SD_DISKS) & 15) << 4;
+ else
+ gd->first_minor = (index & 15) << 4;
gd->minors = 16;
gd->fops = &sd_fops;

- if (index >= 26) {
+ if (index < 26) {
+ sprintf(gd->disk_name, "sd%c", 'a' + index % 26);
+ } else if (index < (26*27)) {
sprintf(gd->disk_name, "sd%c%c",
'a' + index/26-1,'a' + index % 26);
} else {
- sprintf(gd->disk_name, "sd%c", 'a' + index % 26);
+ const unsigned int m1 = (index/ 26 - 1) / 26 - 1;
+ const unsigned int m2 = (index / 26 - 1) % 26;
+ const unsigned int m3 = index % 26;
+ sprintf(gd->disk_name, "sd%c%c%c",
+ 'a' + m1, 'a' + m2, 'a' + m3);
}

strcpy(gd->devfs_name, sdp->devfs_name);

_