Re: pnfs LD partial sector write

[Boaz Harrosh <bharrosh@panasas.com>]

On 07/26/2012 04:57 PM, Peng Tao wrote:

> On Thu, Jul 26, 2012 at 8:16 PM, Boaz Harrosh <bharrosh@panasas.com> wrote:
>> On 07/26/2012 11:25 AM, Peng Tao wrote:
>>
>>> For these two sectors, I need to allocate two pages... Just look at
>>> struct bio_vec.
>>>
>>
>>
>> NO! I know all about bio_vecs
>>
>> You need 1024 bytes, and 2 x one entry BIOs which is a few bytes, where
>> did you get the "two pages" from?
>>
> What do you put int bio_vec->bv_page? Even if you just use 512 bytes
> of a page, it is still allocated page.
> 


No!!

You just use bio_map_kern or in one go blk_rq_map_kern() with any: kmalloc,
stack, or kernel pointer. And that's that. It will take what it will take.

Two such BIOs can use the same page different regions, or a small region
sharing a page with other kmalloc allocations.

I don't see how you got your idea from?

And for the bio itself you use bio_kmalloc(GFP_KERNEL/GFP_NOIO, numentries);
which will give you one BIO + bio_vects in one allocation.

And that is that

You should give me more credit
Boaz