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Re: [dm-devel] [PATCH] block: set the bounce_pfn to the actual DMA limit rather than to max memory



On 2010-09-24 21:20, Malahal Naineni wrote:
> Jens Axboe [jaxboe fusionio com] wrote:
>>> This patch also _fixed_ our problem. So we are fine with either patch,
>>> but this patch is preferred as it enables more request merges. Also,
>>> both patches maybe needed for some configurations.
>>
>> Plus it doesn't needlessly bounce, that's the real problem you want to
>> fix. I have applied this thread patch to for-2.6.37/core, thanks.
> 
> There is a shortcut check in blk_queue_bounce() that uses blk_max_pfn to
> return without doing anything.  blk_max_pfn is not updated when we do
> hot-plug memory add, so bounce buffers are NOT really used in our case
> (thankfully)! 

Any reason we can't just add a hot mem add notifier and update the block
copies when we need to?

-- 
Jens Axboe


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