Large JFFS2 filesystem problem

Hi all.

A while back I posted a message about some problems we were having mounting a large JFFS2 filesystem on a NAND device. We want to treat up to 16 128MB devices as a single device, and have a filesystem on that device (i.e a total of 2 Gig)

However, I've found that if I try to use more than two of these devices, then I can no longer mount a JFFS2 filesystem on the device.

After some debugging, it appears that the kmalloc in jffs2_scan_medium fails, trying to allocate 256K of memory. Elsewhere, there is a comment that the maximum that kmalloc can return is 128K, so this is obviously incorrect.

Is this a limitation in the size of a JFFS2 filesystem, or is this an error? It seems to me that this code:

/*
* Check, if we have to concatenate physical blocks to larger virtual
blocks
* to reduce the memorysize for c->blocks. (kmalloc allows max. 128K
allocation)
*/
c->sector_size = c->mtd->erasesize;
blocks = c->flash_size / c->sector_size;

while ((blocks * sizeof (struct jffs2_eraseblock)) > (128 * 1024)) {
	blocks >>= 1;
	c->sector_size <<= 1;
}	

could be the source of the proble, because while it decreases the number of blocks, it increases the sector size, and it is this sector size that is used in the kmalloc line that fails.

Previously, someone recommended waiting for YAFFS2, as this is likely to be more efficient with large filesystems. Does anyone have any idea as to when this is likely to be available?

Many thanks.

Andy

Sure, the combination of sector size and number of sectors in relation to the maximum allocation size of 128K is the limitation.

It should be easy to fix the scan code. All we have to do is to reduce the chunk size which we read in one go. The functionality to do so is already there and its simple to make it work

Can you try the following patch ?
Please let me know if it works.

Index: scan.c
===================================================================
RCS file: /home/cvs/mtd/fs/jffs2/scan.c,v
retrieving revision 1.110

diff -u -r1.110 scan.c
@@ -104,6 +104,10 @@
                else
                        buf_size = PAGE_SIZE;
  
+               /* Respect kmalloc limitations */
+               if (buf_size > 128*1024)
+                       buf_size = 128*1024;
+
                D1(printk(KERN_DEBUG "Allocating readbuf of %d bytes\n",

buf_size));
                flashbuf = kmalloc(buf_size, GFP_KERNEL);
                if (!flashbuf)

Ask on the YAFFS mailing list.

tglx

Hi,

[snip patch]

Apologies...I didn't read the code fully enough to realise that it would use that block size in a loop to read the entire flash. I changed the 'kmalloc' to a 'vmalloc' and this appeared to work. Your patch also has the desired effect.

Ok, I'll do this.

Thanks.

Andy

Thanks, fixed in CVS

tglx

I've tried to join this list, and am still waiting for the promised 'confirmation' e-mail.

Is some human intervention required?

Andy