Re: How to map high memory for block io

[Pierre Ossman]

Pierre Ossman wrote:
> Russell King wrote:
>   
>> On Fri, Jan 27, 2006 at 09:22:06PM +0100, Jens Axboe wrote:
>>   
>>     
>>> That is definitely valid, same goes for the bio_vec structure. They map
>>> _a_ page, after all :-)
>>>     
>>>       
>> Okay.  Pierre - are you saying that you have an sg entry where
>> sg->offset + sg->length > PAGE_SIZE, and hence is causing you to
>> cross a page boundary?
>>
>>   
>>     
>
> That, and sg->length > PAGE_SIZE. On highmem systems this causes all
> kinds of funky behaviour. Usually just bogus data in the buffers though.
>
>   

Test done here, few minutes ago. Added this to the wbsd driver in its
kmap routine:

    if ((host->cur_sg->offset + host->cur_sg->length) > PAGE_SIZE)
        printk(KERN_DEBUG "wbsd: Big sg: %d, %d\n",
            host->cur_sg->offset, host->cur_sg->length);

got:

[17385.425389] wbsd: Big sg: 0, 8192
[17385.436849] wbsd: Big sg: 0, 7168
[17385.436859] wbsd: Big sg: 0, 7168
[17385.454029] wbsd: Big sg: 2560, 5632
[17385.454216] wbsd: Big sg: 2560, 5632

And so on.

Rgds
Pierre

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