Re: nand_update_bbt fix

[Artem Bityutskiy <dedekind1@gmail.com>]

On Mon, 2009-08-10 at 18:04 -0500, Andrew McKay wrote:
> Hello,
> 
> For NAND parts with 2K pages or larger, kmalloc of one erase block will exceed 
> 128K and fail.  A vmalloc is used in nand_scan_bbt to allocate enough memory for 
> one erase block.  This should likely be the case for nand_update_bbt as well.

I think this is not about parts with 2K pages, but about parts with
256KiB eraseblocks.

> diff --git a/drivers/mtd/nand/nand_bbt.c b/drivers/mtd/nand/nand_bbt.c
> index 55c23e5..43b8d08 100644
> --- a/drivers/mtd/nand/nand_bbt.c
> +++ b/drivers/mtd/nand/nand_bbt.c
> @@ -1030,7 +1030,7 @@ int nand_update_bbt(struct mtd_info *mtd, loff_t offs)
>    /* Allocate a temporary buffer for one eraseblock incl. oob */
>    len = (1 << this->bbt_erase_shift);
>    len += (len >> this->page_shift) * mtd->oobsize;
> - buf = kmalloc(len, GFP_KERNEL);
> + buf = vmalloc(len);
>    if (!buf) {
>      printk(KERN_ERR "nand_update_bbt: Out of memory\n");
>      return -ENOMEM;
> @@ -1063,7 +1063,7 @@ int nand_update_bbt(struct mtd_info *mtd, loff_t offs)
>    }
> 
>    out:
> - kfree(buf);
> + vfree(buf);
>    return res;
>   }

I would disagree with this patch. Other people are fighting against
vmalloc, because they want to do DMA in their drivers, but they cannot.
I've CCed Zhang who is doing the opposite to what you do.

I think you should instead split the array on several smaller parts
and work with those parts. And since this is a very common task in
MTD, it is better to create a helper library.

You may also take a look at what I suggested to Zhang:
http://lists.infradead.org/pipermail/linux-mtd/2009-August/026845.html

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)