Re: [PATCH] orangefs: convert get_user_pages() --> pin_user_pages()

[John Hubbard]

On 2020-05-17 23:01, John Hubbard wrote:

This code was using get_user_pages*(), in a "Case 2" scenario
(DMA/RDMA), using the categorization from [1]. That means that it's
time to convert the get_user_pages*() + put_page() calls to
pin_user_pages*() + unpin_user_pages() calls.

Oops, actually, maybe that description is wrong. This is probably
closer to "Case 1: Direct IO"...right? I don't see an O_DIRECT
anywhere, but there is an ioctl to do ORANGEFS_DEV_MAP, which seems
like effectively it's doing Direct IO.

(I got lulled into commit log complacency, due to sending quite a few
non-filesystem patches that were Case 2.)


thanks,
--
John Hubbard
NVIDIA

There is some helpful background in [2]: basically, this is a small
part of fixing a long-standing disconnect between pinning pages, and
file systems' use of those pages.

[1] Documentation/core-api/pin_user_pages.rst

[2] "Explicit pinning of user-space pages":
     https://lwn.net/Articles/807108/

Signed-off-by: John Hubbard <jhubb...@nvidia.com>
---

  fs/orangefs/orangefs-bufmap.c | 9 +++------
  1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/fs/orangefs/orangefs-bufmap.c b/fs/orangefs/orangefs-bufmap.c
index 2bb916d68576..538e839590ef 100644
--- a/fs/orangefs/orangefs-bufmap.c
+++ b/fs/orangefs/orangefs-bufmap.c
@@ -168,10 +168,7 @@ static DEFINE_SPINLOCK(orangefs_bufmap_lock);
  static void
  orangefs_bufmap_unmap(struct orangefs_bufmap *bufmap)
  {
-       int i;
-
-       for (i = 0; i < bufmap->page_count; i++)
-               put_page(bufmap->page_array[i]);
+       unpin_user_pages(bufmap->page_array, bufmap->page_count);
  }

static void

@@ -268,7 +265,7 @@ orangefs_bufmap_map(struct orangefs_bufmap *bufmap,
        int offset = 0, ret, i;

/* map the pages */

-       ret = get_user_pages_fast((unsigned long)user_desc->ptr,
+       ret = pin_user_pages_fast((unsigned long)user_desc->ptr,
                             bufmap->page_count, FOLL_WRITE, 
bufmap->page_array);

if (ret < 0)

@@ -280,7 +277,7 @@ orangefs_bufmap_map(struct orangefs_bufmap *bufmap,

for (i = 0; i < ret; i++) {

                        SetPageError(bufmap->page_array[i]);
-                       put_page(bufmap->page_array[i]);
+                       unpin_user_page(bufmap->page_array[i]);
                }
                return -ENOMEM;
        }