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Re: [dm-devel] [PATCH 2/7] dm: add reserved_rq_based_ios module parameter



On Thu, Sep 12 2013 at  6:45pm -0400,
Mikulas Patocka <mpatocka redhat com> wrote:

> I think this is too complicated.
> 
> dm-bufio uses similar approach like this patch - but in dm-bufio the code 
> path is performance critical, we don't want to recalculate memory size 
> with each i/o request.
> 
> Here it is not performance critical, so I'd drop the mutex, drop the 
> latch, drop the function __reserved_request_based_ios_refresh and add only 
> these lines:
> 
> pool_size = ACCESS_ONCE(reserved_rq_based_ios);
> if (!pool_size) pool_size = RESERVED_REQUEST_BASED_IOS;

Could be I'm missing something but isn't the locking about correctness
rather than performance?

Also, using the latch enables the dm_get_reserved_rq_based_ios()
interface that is used in patch 5.

Mike


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