linux-kernel - Re: [PATCH v3 6/6] gfs2: Replace kmap_atomic() by kmap_local_page() in gfs2_write_buf_to

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Date:   Sat, 01 Jul 2023 15:54:06 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Bob Peterson <rpeterso@...hat.com>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        cluster-devel@...hat.com, linux-kernel@...r.kernel.org,
        Deepak R Varma <drv@...lo.com>
Cc:     Ira Weiny <ira.weiny@...el.com>,
        Sumitra Sharma <sumitraartsy@...il.com>,
        Deepak R Varma <drv@...lo.com>
Subject: Re: [PATCH v3 6/6] gfs2: Replace kmap_atomic() by kmap_local_page() in
 gfs2_write_buf_to_page

On giovedì 29 giugno 2023 23:52:27 CEST Deepak R Varma wrote:
> kmap_atomic() is deprecated in favor of kmap_local_{folio,page}().

Deepak,

Again please refer to documentation and/or Ira's deprecation patch. The 
reasons why are in one of my previous messages.

> Therefore, replace kmap_atomic() with kmap_local_page() in
> gfs2_write_buf_to_page().
> 
> kmap_atomic() disables page-faults and preemption (the latter only for
> !PREEMPT_RT kernels), However, the code within the mapping/un-mapping in
> gfs2_write_buf_to_page() does not depend on the above-mentioned side
> effects.
> 
> Therefore, a mere replacement of the old API with the new one is all that
> is required (i.e., there is no need to explicitly add any calls to
> pagefault_disable() and/or preempt_disable()).
>
> Suggested-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
> Signed-off-by: Deepak R Varma <drv@...lo.com>
> ---
> Changes in v3:
>    - Patch included in patch set
> 
> Changes in v2:
>    - None
> 
> 
>  fs/gfs2/quota.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c
> index 386ca770ce2e..e5767133aeea 100644
> --- a/fs/gfs2/quota.c
> +++ b/fs/gfs2/quota.c
> @@ -764,10 +764,10 @@ static int gfs2_write_buf_to_page(struct gfs2_inode 
*ip,
> unsigned long index, }
> 
>  	/* Write to the page, now that we have setup the buffer(s) */
> -	kaddr = kmap_atomic(page);
> +	kaddr = kmap_local_page(page);
>
Well, if this page could come from HIGHMEM, how about memcpy_to_page()? 
Otherwise, (if it cannot come from HIGHMEM) we don't need to kmap*() it. 

Can you please take a look at the allocation's flags?

Thanks,

Fabio
>
>  	memcpy(kaddr + off, buf, bytes);
>  	flush_dcache_page(page);
> -	kunmap_atomic(kaddr);
> +	kunmap_local(kaddr);
>  	unlock_page(page);
>  	put_page(page);
> 
> --
> 2.34.1