Re: [PATCH 1/3] block: loop: use kmap(page) instead of page_address(page)

[Ming Lei]

On Tue, Mar 24, 2015 at 6:29 PM, Christoph Hellwig <hch@xxxxxx> wrote:
> On Sun, Mar 22, 2015 at 04:14:52PM +0800, Ming Lei wrote:
>> The raw page allocated in lo_send() can be a highmem page,
>> so kmap(page) should be used for read/write on the page.
>>
>> Also the patch removes kmap()/kunmap() in lo_send() because
>> it isn't needed at all.
>
> The description seems odd, what it seems to do is to shift the
> kmap from lo_send into do_lo_send_write.  This does not seem

Looks I ignore the fact which kmap() can setup page_address(),
so this change isn't needed, please ignore the patch.

> very useful as it now means a kmap per segment instead of just
> a single one per I/O.  What would make more sense is to just
> not allocate a highmem page.

On 32bit system, this still may cause pressure on page allocation, since
requests are handled concurrently now after using workqueue.

But it is a good idea to keep kmap() per segment, and will do that in v2.

Thanks,
Ming Lei
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