Messages in this thread | | | Date | Fri, 17 Apr 2015 09:17:09 -0600 | From | Jens Axboe <> | Subject | Re: [PATCH 3/6] direct-io: add support for write stream IDs |
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On 04/10/2015 05:50 PM, Ming Lin wrote: > On Wed, Mar 25, 2015 at 7:26 AM, Jens Axboe <axboe@kernel.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@fb.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?
Because the assumption is that, in general, the specific file is a good indication of the data lifetime, if someone has already set that. It's a better guess than writing without any stream attached.
> That change causes problem for direct IO, for example > > process 1: > fd = open("/dev/nvme0n1", O_DIRECT...); > //set stream_id 1 > fadvise(fd, 1, 0, POSIX_FADV_STREAMID); > pwrite(fd, ....); > > process 2: > fd = open("/dev/nvme0n1", O_DIRECT...); > //should be legacy stream_id 0 > pwrite(fd, ....); > > But now process 2 also see stream_id 1, which is wrong.
I guess for that case, it is a problem. Basically the fallback breaks down for full block devices, or huge files that are used as a general backing store (like a vm image, for instance). Hmm, not sure what the right solution would be here, or if there really is one. It's probably best NOT to do the fallback after all.
-- Jens Axboe
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