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From: Christoph Hellwig <hch@infradead.org>
To: Jens Axboe <axboe@kernel.dk>
Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	hch@infradead.org, akpm@linux-foundation.org
Subject: Re: [PATCH 3/3] iomap: use filemap_range_needs_writeback() for O_DIRECT reads
Date: Tue, 9 Feb 2021 07:51:19 +0000	[thread overview]
Message-ID: <20210209075119.GC1696555@infradead.org> (raw)
In-Reply-To: <20210209023008.76263-4-axboe@kernel.dk>

On Mon, Feb 08, 2021 at 07:30:08PM -0700, Jens Axboe wrote:
> +		if (iocb->ki_flags & IOCB_NOWAIT) {
> +			if (filemap_range_needs_writeback(mapping, pos, end)) {
> +				ret = -EAGAIN;
> +				goto out_free_dio;
> +			}
> +			flags |= IOMAP_NOWAIT;
> +		}
>  		if (iter_is_iovec(iter))
>  			dio->flags |= IOMAP_DIO_DIRTY;
>  	} else {
> +		if (iocb->ki_flags & IOCB_NOWAIT) {
> +			if (filemap_range_has_page(mapping, pos, end)) {
> +				ret = -EAGAIN;
> +				goto out_free_dio;
> +			}
> +			flags |= IOMAP_NOWAIT;
> +		}
> +
>  		flags |= IOMAP_WRITE;
>  		dio->flags |= IOMAP_DIO_WRITE;
>  
> @@ -478,14 +493,6 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
>  			dio->flags |= IOMAP_DIO_WRITE_FUA;
>  	}
>  
> -	if (iocb->ki_flags & IOCB_NOWAIT) {
> -		if (filemap_range_has_page(mapping, pos, end)) {
> -			ret = -EAGAIN;
> -			goto out_free_dio;
> -		}
> -		flags |= IOMAP_NOWAIT;
> -	}

looking at this I really hate the scheme with the potential racyness
and duplicated page looksups.

Why can't we pass a nonblock flag to filemap_write_and_wait_range
and invalidate_inode_pages2_range that makes them return -EAGAIN
when they would block to clean this whole mess up?

  reply	other threads:[~2021-02-09  7:52 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-09  2:30 [PATCHSET v2 0/3] Improve IOCB_NOWAIT " Jens Axboe
2021-02-09  2:30 ` [PATCH 1/3] mm: provide filemap_range_needs_writeback() helper Jens Axboe
2021-02-09  7:47   ` Christoph Hellwig
2021-02-09 14:30     ` Jens Axboe
2021-02-09  2:30 ` [PATCH 2/3] mm: use filemap_range_needs_writeback() for O_DIRECT reads Jens Axboe
2021-02-09  7:48   ` Christoph Hellwig
2021-02-09 14:27     ` Jens Axboe
2021-02-09  2:30 ` [PATCH 3/3] iomap: " Jens Axboe
2021-02-09  7:51   ` Christoph Hellwig [this message]
2021-02-09 14:29     ` Jens Axboe
2021-02-09 19:55 ` [PATCHSET v2 0/3] Improve IOCB_NOWAIT " Andrew Morton
2021-02-09 20:11   ` Jens Axboe
2021-02-10  8:07     ` Sedat Dilek
2021-02-10  8:07       ` Sedat Dilek
2021-02-10 14:47       ` Jens Axboe
2021-02-24 16:44 [PATCHSET v3 " Jens Axboe
2021-02-24 16:44 ` [PATCH 3/3] iomap: use filemap_range_needs_writeback() for " Jens Axboe
2021-02-24 17:25   ` Jan Kara

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