linux-kernel - Re: [PATCH 3/4] infiniband/mm: convert to the new put_user

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Date:   Mon, 1 Oct 2018 10:35:02 -0400
From:   Dennis Dalessandro <dennis.dalessandro@...el.com>
To:     John Hubbard <jhubbard@...dia.com>, Jason Gunthorpe <jgg@...pe.ca>,
        john.hubbard@...il.com
Cc:     Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...nel.org>,
        Christopher Lameter <cl@...ux.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jan Kara <jack@...e.cz>, Al Viro <viro@...iv.linux.org.uk>,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, Doug Ledford <dledford@...hat.com>,
        Mike Marciniszyn <mike.marciniszyn@...el.com>,
        Christian Benvenuti <benve@...co.com>
Subject: Re: [PATCH 3/4] infiniband/mm: convert to the new put_user_page()
 call

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@...il.com wrote:
>>> From: John Hubbard <jhubbard@...dia.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@...el.com>