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Date:   Wed, 11 Jan 2023 00:11:48 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
Cc:     Benjamin LaHaise <bcrl@kvack.org>, linux-aio@kvack.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        "Venkataramanan, Anirudh" <anirudh.venkataramanan@intel.com>,
        Ira Weiny <ira.weiny@intel.com>, Jeff Moyer <jmoyer@redhat.com>
Subject: Re: [PATCH v2] fs/aio: Replace kmap{,_atomic}() with
 kmap_local_page()
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References: <20230109175629.9482-1-fmdefrancesco@gmail.com>
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On Mon, Jan 09, 2023 at 06:56:29PM +0100, Fabio M. De Francesco wrote:

> -	ring = kmap_atomic(ctx->ring_pages[0]);
> +	ring = kmap_local_page(ctx->ring_pages[0]);
>  	ring->nr = nr_events;	/* user copy */
>  	ring->id = ~0U;
>  	ring->head = ring->tail = 0;
> @@ -575,7 +575,7 @@ static int aio_setup_ring(struct kioctx *ctx, unsigned int nr_events)
>  	ring->compat_features = AIO_RING_COMPAT_FEATURES;
>  	ring->incompat_features = AIO_RING_INCOMPAT_FEATURES;
>  	ring->header_length = sizeof(struct aio_ring);
> -	kunmap_atomic(ring);
> +	kunmap_local(ring);
>  	flush_dcache_page(ctx->ring_pages[0]);

I wonder if it would be more readable as memcpy_to_page(), actually...
>  
>  	return 0;
> @@ -678,9 +678,9 @@ static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm)
>  					 * we are protected from page migration
>  					 * changes ring_pages by ->ring_lock.
>  					 */
> -					ring = kmap_atomic(ctx->ring_pages[0]);
> +					ring = kmap_local_page(ctx->ring_pages[0]);
>  					ring->id = ctx->id;
> -					kunmap_atomic(ring);
> +					kunmap_local(ring);

Incidentally, does it need flush_dcache_page()?