Re: [PATCH v2] orangefs: convert get_user_pages() --> pin_user_pages()

[John Hubbard]

On 2020-05-22 20:59, John Hubbard wrote:

This code was using get_user_pages*(), in a "Case 1" scenario
(Direct IO), 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.

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/

Cc: Mike Marshall <hub...@omnibond.com>
Cc: Martin Brandenburg <mar...@omnibond.com>
Cc: de...@lists.orangefs.org
Cc: linux-fsde...@vger.kernel.org
Signed-off-by: John Hubbard <jhubb...@nvidia.com>
---

Hi,

Note that I have only compile-tested this patch, although that does
also include cross-compiling for a few other arches.

An update on the run-time testing: Just now, I got basic orangefs tests
running in xfstests, with this patch applied, and it all looks normal.

thanks,
--
John Hubbard
NVIDIA

Changes since v1 [3]: correct the commit description, so that
it refers to "Case 1" instead of "Case 2".


[3] https://lore.kernel.org/r/20200518060139.2828423-1-jhubb...@nvidia.com

thanks,
John Hubbard
NVIDIA

  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;
        }