linux-kernel - Re: [RFC PATCH 2/2] mm/gup: introduce vaddr_pin_pages

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Date:   Thu, 15 Aug 2019 19:14:08 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jérôme Glisse <jglisse@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-fsdevel@...r.kernel.org>, <linux-rdma@...r.kernel.org>
Subject: Re: [RFC PATCH 2/2] mm/gup: introduce vaddr_pin_pages_remote()

On 8/15/19 10:41 AM, John Hubbard wrote:
> On 8/15/19 10:32 AM, Ira Weiny wrote:
>> On Thu, Aug 15, 2019 at 03:35:10PM +0200, Jan Kara wrote:
>>> On Thu 15-08-19 15:26:22, Jan Kara wrote:
>>>> On Wed 14-08-19 20:01:07, John Hubbard wrote:
>>>>> On 8/14/19 5:02 PM, John Hubbard wrote:
...
>> Ok just to make this clear I threw up my current tree with your patches here:
>>
>> https://github.com/weiny2/linux-kernel/commits/mmotm-rdmafsdax-b0-v4
>>
>> I'm talking about dropping the final patch:
>> 05fd2d3afa6b rdma/umem_odp: Use vaddr_pin_pages_remote() in ODP
>>
>> The other 2 can stay.  I split out the *_remote() call.  We don't have a user
>> but I'll keep it around for a bit.
>>
>> This tree is still WIP as I work through all the comments.  So I've not changed
>> names or variable types etc...  Just wanted to settle this.
>>
> 
> Right. And now that ODP is not a user, I'll take a quick look through my other
> call site conversions and see if I can find an easy one, to include here as
> the first user of vaddr_pin_pages_remote(). I'll send it your way if that
> works out.
> 

OK, there was only process_vm_access.c, plus (sort of) Bharath's sgi-gru
patch, maybe eventually [1].  But looking at process_vm_access.c, I think 
it is one of the patches that is no longer applicable, and I can just
drop it entirely...I'd welcome a second opinion on that...

So we might be all out of potential users for vaddr_pin_pages_remote()!

For quick reference, it looks like this:
 
diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
index 357aa7bef6c0..4d29d54ec93f 100644
--- a/mm/process_vm_access.c
+++ b/mm/process_vm_access.c
@@ -96,7 +96,7 @@ static int process_vm_rw_single_vec(unsigned long addr,
                flags |= FOLL_WRITE;
 
        while (!rc && nr_pages && iov_iter_count(iter)) {
-               int pages = min(nr_pages, max_pages_per_loop);
+               int pinned_pages = min(nr_pages, max_pages_per_loop);
                int locked = 1;
                size_t bytes;
 
@@ -106,14 +106,15 @@ static int process_vm_rw_single_vec(unsigned long addr,
                 * current/current->mm
                 */
                down_read(&mm->mmap_sem);
-               pages = get_user_pages_remote(task, mm, pa, pages, flags,
-                                             process_pages, NULL, &locked);
+               pinned_pages = get_user_pages_remote(task, mm, pa, pinned_pages,
+                                                    flags, process_pages, NULL,
+                                                    &locked);
                if (locked)
                        up_read(&mm->mmap_sem);
-               if (pages <= 0)
+               if (pinned_pages <= 0)
                        return -EFAULT;
 
-               bytes = pages * PAGE_SIZE - start_offset;
+               bytes = pinned_pages * PAGE_SIZE - start_offset;
                if (bytes > len)
                        bytes = len;
 
@@ -122,10 +123,9 @@ static int process_vm_rw_single_vec(unsigned long addr,
                                         vm_write);
                len -= bytes;
                start_offset = 0;
-               nr_pages -= pages;
-               pa += pages * PAGE_SIZE;
-               while (pages)
-                       put_page(process_pages[--pages]);
+               nr_pages -= pinned_pages;
+               pa += pinned_pages * PAGE_SIZE;
+               put_user_pages(process_pages, pinned_pages);
        }
 
        return rc;


[1] https://lore.kernel.org/r/1565379497-29266-2-git-send-email-linux.bhar@gmail.com

thanks,
-- 
John Hubbard
NVIDIA