Re: [PATCH 3/4] infiniband/mm: convert to the new put_user_page() call

From: John Hubbard <jhubbard@nvidia.com>
To: Dennis Dalessandro <dennis.dalessandro@intel.com>,
	Jason Gunthorpe <jgg@ziepe.ca>,
	john.hubbard@gmail.com
Cc: Matthew Wilcox <willy@infradead.org>,
	Michal Hocko <mhocko@kernel.org>,
	Christopher Lameter <cl@linux.com>,
	Dan Williams <dan.j.williams@intel.com>, Jan Kara <jack@suse.cz>,
	Al Viro <viro@zeniv.linux.org.uk>,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
	linux-rdma <linux-rdma@vger.kernel.org>,
	linux-fsdevel@vger.kernel.org, Doug Ledford <dledford@redhat.com>,
	Mike Marciniszyn <mike.marciniszyn@intel.com>,
	Christian Benvenuti <benve@cisco.com>
Subject: Re: [PATCH 3/4] infiniband/mm: convert to the new put_user_page() call
Date: Tue, 2 Oct 2018 22:40:43 -0700	[thread overview]
Message-ID: <e5ffa56e-ae51-6e2c-e6a9-efbdf9317ae0@nvidia.com> (raw)
In-Reply-To: <ed9cbf0a-acc9-1b26-a7fc-e8f89f577ce9@intel.com>

On 10/1/18 7:35 AM, Dennis Dalessandro wrote:
> On 9/28/2018 11:12 PM, John Hubbard wrote:
>> On 9/28/18 8:39 AM, Jason Gunthorpe wrote:
>>> On Thu, Sep 27, 2018 at 10:39:47PM -0700, john.hubbard@gmail.com wrote:
>>>> From: John Hubbard <jhubbard@nvidia.com>
>> [...]
>>>>
>>>> diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
>>>> index a41792dbae1f..9430d697cb9f 100644
>>>> +++ b/drivers/infiniband/core/umem.c
>>>> @@ -60,7 +60,7 @@ static void __ib_umem_release(struct ib_device *dev, struct ib_umem *umem, int d
>>>>           page = sg_page(sg);
>>>>           if (!PageDirty(page) && umem->writable && dirty)
>>>>               set_page_dirty_lock(page);
>>>> -        put_page(page);
>>>> +        put_user_page(page);
>>>
>>> Would it make sense to have a release/put_user_pages_dirtied to absorb
>>> the set_page_dity pattern too? I notice in this patch there is some
>>> variety here, I wonder what is the right way?
>>>
>>> Also, I'm told this code here is a big performance bottleneck when the
>>> number of pages becomes very long (think >> GB of memory), so having a
>>> future path to use some kind of batching/threading sound great.
>>>
>>
>> Yes. And you asked for this the first time, too. Consistent! :) Sorry for
>> being slow to pick it up. It looks like there are several patterns, and
>> we have to support both set_page_dirty() and set_page_dirty_lock(). So
>> the best combination looks to be adding a few variations of
>> release_user_pages*(), but leaving put_user_page() alone, because it's
>> the "do it yourself" basic one. Scatter-gather will be stuck with that.
>>
>> Here's a differential patch with that, that shows a nice little cleanup in
>> a couple of IB places, and as you point out, it also provides the hooks for
>> performance upgrades (via batching) in the future.
>>
>> Does this API look about right?
> 
> I'm on board with that and the changes to hfi1 and qib.
> 
> Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>

Hi Dennis, thanks for the review!

I'll add those new routines in and send out a v2 soon, now that it appears, from 
the recent discussion, that this aspect of the approach is still viable.

thanks,
-- 
John Hubbard
NVIDIA