Re: [PATCH v7 1/6] fs: direct-io: don't dirtying pages for ITER_BVEC/ITER_KVEC direct read

[Dave Kleikamp <dave.kleikamp@oracle.com>]

On 07/16/2015 10:37 AM, Ming Lei wrote:
> When direct read IO is submitted from kernel, it is often
> unnecessary to dirty pages, for example of loop, dirtying pages
> have been considered in the upper filesystem(over loop) side
> already, and they don't need to be dirtied again.
> 
> So this patch doesn't dirtying pages for ITER_BVEC/ITER_KVEC
> direct read, and loop should be the 1st case to use ITER_BVEC/ITER_KVEC
> for direct read I/O.
> 
> The patch is based on previous Dave's patch.
> 
> Cc: Dave Kleikamp <dave.kleikamp@oracle.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Ming Lei <ming.lei@canonical.com>

Reviewed-by: Dave Kleikamp <dave.kleikamp@oracle.com>

> ---
>  fs/direct-io.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 745d234..07e4b28 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -120,6 +120,7 @@ struct dio {
>  	int page_errors;		/* errno from get_user_pages() */
>  	int is_async;			/* is IO async ? */
>  	bool defer_completion;		/* defer AIO completion to workqueue? */
> +	bool should_dirty;		/* if pages should be dirtied */
>  	int io_error;			/* IO error in completion path */
>  	unsigned long refcount;		/* direct_io_worker() and bios */
>  	struct bio *bio_list;		/* singly linked via bi_private */
> @@ -393,7 +394,7 @@ static inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
>  	dio->refcount++;
>  	spin_unlock_irqrestore(&dio->bio_lock, flags);
>  
> -	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)
> @@ -464,13 +465,14 @@ 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) {
>  		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);
>  			page_cache_release(page);
>  		}
> @@ -1217,6 +1219,7 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
>  	spin_lock_init(&dio->bio_lock);
>  	dio->refcount = 1;
>  
> +	dio->should_dirty = (iter->type == ITER_IOVEC);
>  	sdio.iter = iter;
>  	sdio.final_block_in_request =
>  		(offset + iov_iter_count(iter)) >> blkbits;
>