Re: [PATCH RFC PKS/PMEM 22/58] fs/f2fs: Utilize new kmap_thread()

[Eric Biggers <ebiggers@xxxxxxxxxx>]

On Fri, Oct 09, 2020 at 12:49:57PM -0700, 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: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> Cc: Chao Yu <chao@xxxxxxxxxx>
> Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> ---
>  fs/f2fs/f2fs.h | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index d9e52a7f3702..ff72a45a577e 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -2410,12 +2410,12 @@ static inline struct page *f2fs_pagecache_get_page(
>  
>  static inline void f2fs_copy_page(struct page *src, struct page *dst)
>  {
> -     char *src_kaddr = kmap(src);
> -     char *dst_kaddr = kmap(dst);
> +     char *src_kaddr = kmap_thread(src);
> +     char *dst_kaddr = kmap_thread(dst);
>  
>       memcpy(dst_kaddr, src_kaddr, PAGE_SIZE);
> -     kunmap(dst);
> -     kunmap(src);
> +     kunmap_thread(dst);
> +     kunmap_thread(src);
>  }

Wouldn't it make more sense to switch cases like this to kmap_atomic()?
The pages are only mapped to do a memcpy(), then they're immediately unmapped.

- Eric