Re: [PATCH v3 2/3] mm: introduce put_user_page*(), placeholder versions

[Jan Kara]

On Fri 05-10-18 19:49:48, john.hubbard@xxxxxxxxx wrote:
> From: John Hubbard <jhubbard@xxxxxxxxxx>
> 
> Introduces put_user_page(), which simply calls put_page().
> This provides a way to update all get_user_pages*() callers,
> so that they call put_user_page(), instead of put_page().
> 
> Also introduces put_user_pages(), and a few dirty/locked variations,
> as a replacement for release_pages(), and also as a replacement
> for open-coded loops that release multiple pages.
> These may be used for subsequent performance improvements,
> via batching of pages to be released.
> 
> This prepares for eventually fixing the problem described
> in [1], and is following a plan listed in [2], [3], [4].
> 
> [1] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()"
> 
> [2] https://lkml.kernel.org/r/20180709080554.21931-1-jhubbard@xxxxxxxxxx
>     Proposed steps for fixing get_user_pages() + DMA problems.
> 
> [3]https://lkml.kernel.org/r/20180710082100.mkdwngdv5kkrcz6n@xxxxxxxxxxxxxx
>     Bounce buffers (otherwise [2] is not really viable).
> 
> [4] https://lkml.kernel.org/r/20181003162115.GG24030@xxxxxxxxxxxxxx
>     Follow-up discussions.
> 
> CC: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> CC: Michal Hocko <mhocko@xxxxxxxxxx>
> CC: Christopher Lameter <cl@xxxxxxxxx>
> CC: Jason Gunthorpe <jgg@xxxxxxxx>
> CC: Dan Williams <dan.j.williams@xxxxxxxxx>
> CC: Jan Kara <jack@xxxxxxx>
> CC: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> CC: Jerome Glisse <jglisse@xxxxxxxxxx>
> CC: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> CC: Ralph Campbell <rcampbell@xxxxxxxxxx>
> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
> ---
>  include/linux/mm.h | 48 ++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 46 insertions(+), 2 deletions(-)

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

Just one nit below:

> +/* Pages that were pinned via get_user_pages*() should be released via
> + * either put_user_page(), or one of the put_user_pages*() routines
> + * below.
> + */

Multi-line comments usually follow formatting:

/*
 * Some text here
 * and more text here...
 */

								Honza
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR