Re: [PATCH v2] fs/aio: Replace kmap{,_atomic}() with kmap_local_page()

From: Jeff Moyer <jmoyer@redhat.com>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>,
	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>
Subject: Re: [PATCH v2] fs/aio: Replace kmap{,_atomic}() with kmap_local_page()
Date: Wed, 11 Jan 2023 09:13:40 -0500	[thread overview]
Message-ID: <x498ri9ma5n.fsf@segfault.boston.devel.redhat.com> (raw)
In-Reply-To: <Y73+xKXDELSd14p1@ZenIV> (Al Viro's message of "Wed, 11 Jan 2023 00:11:48 +0000")

Hi, Al,

Al Viro <viro@zeniv.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.

>>  
>>  	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()?

Yes, good catch.

Cheers,
Jeff