Re: [PATCH RFC PKS/PMEM 33/58] fs/cramfs: Utilize new kmap_thread()

[Dan Williams <dan.j.williams@xxxxxxxxx>]

On Fri, Oct 9, 2020 at 12:52 PM <ira.weiny@xxxxxxxxx> wrote:
>
> From: Ira Weiny <ira.weiny@xxxxxxxxx>
>
> The kmap() calls in this FS are localized to a single thread.  To avoid
> the over head of global PKRS updates use the new kmap_thread() call.
>
> Cc: Nicolas Pitre <nico@xxxxxxxxxxx>
> Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> ---
>  fs/cramfs/inode.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c
> index 912308600d39..003c014a42ed 100644
> --- a/fs/cramfs/inode.c
> +++ b/fs/cramfs/inode.c
> @@ -247,8 +247,8 @@ static void *cramfs_blkdev_read(struct super_block *sb, 
> unsigned int offset,
>                 struct page *page = pages[i];
>
>                 if (page) {
> -                       memcpy(data, kmap(page), PAGE_SIZE);
> -                       kunmap(page);
> +                       memcpy(data, kmap_thread(page), PAGE_SIZE);
> +                       kunmap_thread(page);

Why does this need a sleepable kmap? This looks like a textbook
kmap_atomic() use case.