linux-kernel - Re: [PATCH 3/6] direct-io: add support for write stream IDs

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Date:	Fri, 10 Apr 2015 17:06:55 -0700
From:	Ming Lin <mlin@...nel.org>
To:	Ming Lin <mlin@...nel.org>
Cc:	Jens Axboe <axboe@...nel.dk>, Dave Chinner <david@...morbit.com>,
	Jens Axboe <axboe@...com>, lkml <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org, ming.l@....samsung.com
Subject: Re: [PATCH 3/6] direct-io: add support for write stream IDs

On Fri, Apr 10, 2015 at 4:50 PM, Ming Lin <mlin@...nel.org> wrote:
> On Wed, Mar 25, 2015 at 7:26 AM, Jens Axboe <axboe@...nel.dk> wrote:
>> On 03/24/2015 08:43 PM, Dave Chinner wrote:
>>>
>>> On Tue, Mar 24, 2015 at 09:27:00AM -0600, Jens Axboe wrote:
>>>>
>>>> Get the streamid from the file, if any, and set it on the bio.
>>>>
>>>> Signed-off-by: Jens Axboe <axboe@...com>
>>>> ---
>>>>   fs/direct-io.c | 4 ++++
>>>>   1 file changed, 4 insertions(+)
>>>>
>>>> diff --git a/fs/direct-io.c b/fs/direct-io.c
>>>> index e181b6b2e297..5d2750346451 100644
>>>> --- a/fs/direct-io.c
>>>> +++ b/fs/direct-io.c
>>>> @@ -77,6 +77,7 @@ struct dio_submit {
>>>>         int reap_counter;               /* rate limit reaping */
>>>>         sector_t final_block_in_request;/* doesn't change */
>>>>         int boundary;                   /* prev block is at a boundary */
>>>> +       int streamid;                   /* Write stream ID */
>>>>         get_block_t *get_block;         /* block mapping function */
>>>>         dio_submit_t *submit_io;        /* IO submition function */
>>>>
>>>> @@ -372,6 +373,8 @@ dio_bio_alloc(struct dio *dio, struct dio_submit
>>>> *sdio,
>>>>
>>>>         sdio->bio = bio;
>>>>         sdio->logical_offset_in_bio = sdio->cur_page_fs_offset;
>>>> +
>>>> +       bio_set_streamid(bio, sdio->streamid);
>>>>   }
>>>>
>>>>   /*
>>>> @@ -1205,6 +1208,7 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb,
>>>> struct inode *inode,
>>>>         sdio.blkbits = blkbits;
>>>>         sdio.blkfactor = i_blkbits - blkbits;
>>>>         sdio.block_in_file = offset >> blkbits;
>>>> +       sdio.streamid = iocb->ki_filp->f_streamid;
>>>
>>>
>>> If iocb->ki_filp->f_streamid is not set, then it should fall back to
>>> whatever is set on the inode->i_streamid.
>
> Why should do the fall back?
>
>>
>>
>> Good point, agree. Will make that change.
>
> Hi Jens,
>
> That change causes problem for direct IO, for example

Actually, buffered write also has problem.

process 1:
fd = open("/mnt/foo.txt", ...);
//set stream_id 1
fadvise(fd, 1, 0, POSIX_FADV_STREAMID);
write(fd, ....);

process 1 exit, but stream_id is still saved in inode

later process 2 starts,
and when writeback it will see stream_id 1 from inode although it
didn't set stream_id at all

process 2:
fd = open("/mnt/foo.txt", ...);
write(fd, ....);

Thanks,
Ming
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