2020-05-17 02:11:19

by John Hubbard

Subject: [PATCH] oradax: convert get_user_pages() --> pin_user_pages()

This code was using get_user_pages_fast(), in a "Case 2" scenario
(DMA/RDMA), using the categorization from [1]. That means that it's
time to convert the get_user_pages_fast() + put_page() calls to
pin_user_pages_fast() + 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: David S. Miller <[email protected]>
Cc: [email protected]
Signed-off-by: John Hubbard <[email protected]>
---
drivers/sbus/char/oradax.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/sbus/char/oradax.c b/drivers/sbus/char/oradax.c
index 8af216287a84..21b7cb6e7e70 100644
--- a/drivers/sbus/char/oradax.c
+++ b/drivers/sbus/char/oradax.c
@@ -410,9 +410,7 @@ static void dax_unlock_pages(struct dax_ctx *ctx, int ccb_index, int nelem)

if (p) {
dax_dbg("freeing page %p", p);
- if (j == OUT)
- set_page_dirty(p);
- put_page(p);
+ unpin_user_pages_dirty_lock(&p, 1, j == OUT);
ctx->pages[i][j] = NULL;
}
}
@@ -425,13 +423,13 @@ static int dax_lock_page(void *va, struct page **p)

dax_dbg("uva %p", va);

- ret = get_user_pages_fast((unsigned long)va, 1, FOLL_WRITE, p);
+ ret = pin_user_pages_fast((unsigned long)va, 1, FOLL_WRITE, p);
if (ret == 1) {
dax_dbg("locked page %p, for VA %p", *p, va);
return 0;
}

- dax_dbg("get_user_pages failed, va=%p, ret=%d", va, ret);
+ dax_dbg("pin_user_pages failed, va=%p, ret=%d", va, ret);
return -1;
}


base-commit: 3d1c1e5931ce45b3a3f309385bbc00c78e9951c6
--
2.26.2

2020-05-17 19:48:23

by David Miller

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

From: John Hubbard <[email protected]>
Date: Sat, 16 May 2020 19:08:29 -0700

> This code was using get_user_pages_fast(), in a "Case 2" scenario
> (DMA/RDMA), using the categorization from [1]. That means that it's
> time to convert the get_user_pages_fast() + put_page() calls to
> pin_user_pages_fast() + 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: David S. Miller <[email protected]>
> Cc: [email protected]
> Signed-off-by: John Hubbard <[email protected]>

Applied to sparc-next, thanks.