linux-kernel - Re: [PATCH v2] fs/aio: Replace kmap{,_atomic}() with kmap_local

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Message-ID: <x494jsxm4am.fsf@segfault.boston.devel.redhat.com>
Date:   Wed, 11 Jan 2023 11:20:17 -0500
From:   Jeff Moyer <jmoyer@...hat.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Benjamin LaHaise <bcrl@...ck.org>, linux-aio@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Venkataramanan\, Anirudh" <anirudh.venkataramanan@...el.com>,
        Ira Weiny <ira.weiny@...el.com>
Subject: Re: [PATCH v2] fs/aio: Replace kmap{,_atomic}() with kmap_local_page()

Al Viro <viro@...iv.linux.org.uk> writes:

> On Wed, Jan 11, 2023 at 09:13:40AM -0500, Jeff Moyer wrote:
>> Hi, Al,
>> 
>> Al Viro <viro@...iv.linux.org.uk> writes:
>> 
>> > 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...
>> 
>> I'm not sure I understand what you're suggesting.
>
> 	memcpy_to_page(ctx->ring_pages[0], 0, &(struct aio_ring){
> 			.nr = nr_events, .id = ~0U, .magic = AIO_RING_MAGIC,
> 			.compat_features = AIO_RING_COMPAT_FEATURES,
> 			.in_compat_features = AIO_RING_INCOMPAT_FEATURES,
> 			.header_length = sizeof(struct aio_ring)},
> 			sizeof(struct aio_ring));
>
> instead of the lines from kmap_atomic to flush_dcache_page...

Thanks for spelling it out.  I guess it's a matter of opinion, but I
don't find that more readable.

Cheers,
Jeff