linux-kernel - RE: [PATCH 4/7] Add stream ID support for buffered mpage/__block_write_full

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Date:	Wed, 25 Mar 2015 22:42:48 +0000
From:	Ming Lin-SSI <ming.l@....samsung.com>
To:	Jens Axboe <axboe@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
CC:	"david@...morbit.com" <david@...morbit.com>
Subject: RE: [PATCH 4/7] Add stream ID support for buffered
 mpage/__block_write_full_page()

> -----Original Message-----
> From: Jens Axboe [mailto:axboe@...com]
> Sent: Wednesday, March 25, 2015 8:08 AM
> To: linux-kernel@...r.kernel.org; linux-fsdevel@...r.kernel.org
> Cc: Ming Lin-SSI; david@...morbit.com; Jens Axboe
> Subject: [PATCH 4/7] Add stream ID support for buffered
> mpage/__block_write_full_page()
> 
> Pass on the inode stream ID to the bio allocation.
> 
> Signed-off-by: Jens Axboe <axboe@...com>
> ---
>  fs/buffer.c | 4 ++--
>  fs/mpage.c  | 1 +
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 20805db2c987..0220925ff26d 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1774,7 +1774,7 @@ static int __block_write_full_page(struct inode
> *inode, struct page *page,
>  	do {
>  		struct buffer_head *next = bh->b_this_page;
>  		if (buffer_async_write(bh)) {
> -			submit_bh(write_op, bh);
> +			_submit_bh(write_op, bh,
> streamid_to_flags(inode_streamid(inode)));
>  			nr_underway++;
>  		}
>  		bh = next;
> @@ -1828,7 +1828,7 @@ recover:
>  		struct buffer_head *next = bh->b_this_page;
>  		if (buffer_async_write(bh)) {
>  			clear_buffer_dirty(bh);
> -			submit_bh(write_op, bh);
> +			_submit_bh(write_op, bh,
> streamid_to_flags(inode_streamid(inode)));
>  			nr_underway++;
>  		}
>  		bh = next;
> diff --git a/fs/mpage.c b/fs/mpage.c
> index 3e79220babac..fba13f4b981d 100644
> --- a/fs/mpage.c
> +++ b/fs/mpage.c
> @@ -605,6 +605,7 @@ alloc_new:
>  				bio_get_nr_vecs(bdev),
> GFP_NOFS|__GFP_HIGH);
>  		if (bio == NULL)
>  			goto confused;
> +		bio_set_streamid(bio, inode_streamid(inode));

This will not work when multiple processes write to the same raw disk.
Let's say 2 process concurrently pwrite to /dev/nvme0n1 with different stream_id.

Process 1:
fd = open("/dev/nvme0n1", ...);
posix_fadvise(fd, stream_id_1, 0, POSIX_FADV_STREAMID);
pwrite( fd, buf1, count1, offset1);

Process 2:
fd = open("/dev/nvme0n1", ...);
posix_fadvise(fd, stream_id_2, 0, POSIX_FADV_STREAMID);
pwrite(fd, buf2, count2, offset2);

One stream_id will overwrite the other one because "inode" is same.

Thanks,
Ming
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