linux-ext4 - Re: [PATCH RFC PKS/PMEM 22/58] fs/f2fs: Utilize new kmap

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Date:   Fri, 9 Oct 2020 14:34:34 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     ira.weiny@...el.com
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Subject: Re: [PATCH RFC PKS/PMEM 22/58] fs/f2fs: Utilize new kmap_thread()

On Fri, Oct 09, 2020 at 12:49:57PM -0700, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> 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@...nel.org>
> Cc: Chao Yu <chao@...nel.org>
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> ---
>  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