linux-kernel - Re: [PATCH v2 2/4] fd/direct-io: introduce should

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Date:	Sun, 25 Jan 2015 05:34:33 -0800
From:	Christoph Hellwig <hch@...radead.org>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	linux-kernel@...r.kernel.org,
	Dave Kleikamp <dave.kleikamp@...cle.com>,
	Jens Axboe <axboe@...nel.dk>, Zach Brown <zab@...bo.net>,
	Christoph Hellwig <hch@...radead.org>,
	Maxim Patlasov <mpatlasov@...allels.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Omar Sandoval <osandov@...ndov.com>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] fd/direct-io: introduce should_dirty for kernel
 aio

On Tue, Jan 13, 2015 at 11:44:46PM +0800, Ming Lei wrote:
>  
> -	if (dio->is_async && dio->rw == READ)
> +	if (dio->is_async && dio->rw == READ && dio->should_dirty)
>  		bio_set_pages_dirty(bio);
>  
>  	if (sdio->submit_io)
> @@ -463,13 +464,14 @@ static int dio_bio_complete(struct dio *dio, struct bio *bio)
>  	if (!uptodate)
>  		dio->io_error = -EIO;
>  
> -	if (dio->is_async && dio->rw == READ) {
> +	if (dio->is_async && dio->rw == READ && dio->should_dirty) {

I'd rather have a ->should_dirrty flag that means we need to call
bio_check_pages_dirty, And set that either if we have a kernel
iovec/bvec or dio->is_async && dio->rw == READ.

But why would we even set this if writing from an iovec?

>  		bio_check_pages_dirty(bio);	/* transfers ownership */
>  	} else {
>  		bio_for_each_segment_all(bvec, bio, i) {
>  			struct page *page = bvec->bv_page;
>  
> -			if (dio->rw == READ && !PageCompound(page))
> +			if (dio->rw == READ && !PageCompound(page) &&
> +					dio->should_dirty)
>  				set_page_dirty_lock(page);

And this unk could also use some explanation.

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