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Date:   Mon, 11 Jan 2021 10:52:05 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Pavel Begunkov <asml.silence@...il.com>
Cc:     linux-block@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        Jonathan Corbet <corbet@....net>, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org, target-devel@...r.kernel.org,
        linux-scsi@...r.kernel.org, linux-doc@...r.kernel.org,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v3 3/7] block/psi: remove PSI annotations from direct IO

On Sat, Jan 09, 2021 at 04:02:59PM +0000, Pavel Begunkov wrote:
> Direct IO does not operate on the current working set of pages managed
> by the kernel, so it should not be accounted as memory stall to PSI
> infrastructure.
> 
> The block layer and iomap direct IO use bio_iov_iter_get_pages()
> to build bios, and they are the only users of it, so to avoid PSI
> tracking for them clear out BIO_WORKINGSET flag. Do same for
> dio_bio_submit() because fs/direct_io constructs bios by hand directly
> calling bio_add_page().
> 
> Reported-by: Christoph Hellwig <hch@...radead.org>
> Suggested-by: Christoph Hellwig <hch@...radead.org>
> Suggested-by: Johannes Weiner <hannes@...xchg.org>
> Reviewed-by: Christoph Hellwig <hch@....de>
> Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
> ---
>  block/bio.c    | 6 ++++++
>  fs/direct-io.c | 2 ++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/block/bio.c b/block/bio.c
> index 1f2cc1fbe283..9f26984af643 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1099,6 +1099,9 @@ static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter)
>   * fit into the bio, or are requested in @iter, whatever is smaller. If
>   * MM encounters an error pinning the requested pages, it stops. Error
>   * is returned only if 0 pages could be pinned.
> + *
> + * It's intended for direct IO, so doesn't do PSI tracking, the caller is
> + * responsible for setting BIO_WORKINGSET if necessary.
>   */
>  int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
>  {
> @@ -1123,6 +1126,9 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
>  
>  	if (is_bvec)
>  		bio_set_flag(bio, BIO_NO_PAGE_REF);
> +
> +	/* don't account direct I/O as memory stall */
> +	bio_clear_flag(bio, BIO_WORKINGSET);
>  	return bio->bi_vcnt ? 0 : ret;
>  }
>  EXPORT_SYMBOL_GPL(bio_iov_iter_get_pages);
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index d53fa92a1ab6..0e689233f2c7 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -426,6 +426,8 @@ static inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
>  	unsigned long flags;
>  
>  	bio->bi_private = dio;
> +	/* don't account direct I/O as memory stall */
> +	bio_clear_flag(bio, BIO_WORKINGSET);
>  
>  	spin_lock_irqsave(&dio->bio_lock, flags);
>  	dio->refcount++;
> -- 
> 2.24.0
> 

Reviewed-by: Ming Lei <ming.lei@...hat.com>

-- 
Ming

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