Re: [Lsf-pc] [LSF/MM ATTEND] block: multipage bvecs

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On Mon, Feb 29, 2016 at 12:45 AM, James Bottomley
<James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote:
> On Sun, 2016-02-28 at 08:29 -0800, Christoph Hellwig wrote:
>> On Sun, Feb 28, 2016 at 08:26:46AM -0800, James Bottomley wrote:
>> > You mean in bio_add_page() the code which currently aggregates
>> > chunks within a page could build a bio vec entry up to the max
>> > segment size?  I think that is reasonable, especially now the bio
>> > splitting code can actually split inside a bio vec entry.
>>
>> Yes.  Kent has an old prototype that did this at:
>>
>> https://evilpiepirate.org/git/linux-bcache.git/log/?h=block_stuff
>>
>> I don't think any of that is reusable as-is, but the basic idea is
>> sounds and very useful.
>
> The basic idea, yes, but the actual code in that tree would still have
> built up bv entries that are too big.  We have to thread bio_add_page()
> with knowledge of the queue limits, which is somewhat hard since
> they're deliberately queue agnostic.  Perhaps some global minimum queue
> segment size would work?

IMO, we can just build contiguous segment simply into one vector because
bio_add_page() in hot path, then compute segments during
bio splitting from submit_bio() path by applying all kinds of queue limit just
like current way.

Thanks
Ming

>
> James
>



-- 
Ming Lei
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