Re: [PATCH v4 0/4] mm/gup: page unpining improvements

[Joao Martins]

On 2/18/21 3:33 PM, Joao Martins wrote:
> On 2/18/21 7:24 AM, Christoph Hellwig wrote:
>> On Fri, Feb 12, 2021 at 01:08:39PM +0000, Joao Martins wrote:
>>> Hey,
>>>
>>> This series improves page unpinning, with an eye on improving MR
>>> deregistration for big swaths of memory (which is bound by the page
>>> unpining), particularly:
>>
>> Can you also take a look at the (bdev and iomap) direct I/O code to
>> make use of this?  It should really help there, with a much wieder use
>> than RDMA.
>>
> Perhaps by bdev and iomap direct I/O using this, you were thinking to replace
> bio_release_pages() which operates on bvecs and hence releasing contiguous pages
> in a bvec at once? e.g. something like from this:
> 
>         bio_for_each_segment_all(bvec, bio, iter_all) {
>                 if (mark_dirty && !PageCompound(bvec->bv_page))
>                         set_page_dirty_lock(bvec->bv_page);
>                 put_page(bvec->bv_page);
>         }
> 
> (...) to this instead:
> 
> 	bio_for_each_bvec_all(bvec, bio, i)
> 		unpin_user_page_range_dirty_lock(bvec->bv_page,
> 			DIV_ROUND_UP(bvec->bv_len, PAGE_SIZE),
> 			mark_dirty && !PageCompound(bvec->bv_page));
> 

Quick correction: It should be put_user_page_range_dirty_lock() given that unpin is
specific to FOLL_PIN users.