On Fri, 2011-11-04 at 02:01 +0800, Jeff Moyer wrote: > Coly Li <i@xxxxxxx> writes: > > > On 2011年11月01日 17:00, Zhu Yanhai Wrote: > >> The current libaio/aio has to be Direct-IO, otherwise it falls back into sync IO. > >> However, the aio core has already been asychronous naturally. This patch adds a complete > >> notify mechanism to implement buffer aio, the main idea is to readahead()-like in > >> io_submit(), counts the non-uptodated pages assocaiated with each iocb, then put each ref > >> in the bio complete path just before unlock_page(), and hook them on to the aio ring buffer > >> finally when the ref drops to zero. In io_getevents(), we call vfs_read() as a safe net > >> since there is still little possibility that the pages had brought in were reclaimed > >> between io_submit() and io_getevents(). > >> > >> I have tested this patch for a while, for the small size random io request, its > >> performance is more or less the same with the traditional aio, for the big io request, > >> the overhead of one extra memory copy arises. > >> > >> I think so far it has at least below obvious drawbacks, > >> > >> * mpage_readpage() is a really narrow interface, I have no way to pass down > >> the new control struct baiocb, so I just put it into struct task_struct and > >> refer it by current() as a workaround. > >> > >> * the do_baio_read() routine is heavily similar with do_generic_file_read(), but > >> the latter is really hard to modify. I think we may stuff these code down into the > >> readahead path to reduce code reduplication. > >> > >> Hopefully the explanations are clear enough and don't muddy the water any worse. > >> I figure the code does need some better comments, and any suggestion are welcome. > >> > >> Signed-off-by: Zhu Yanhai <gaoyang.zyh@xxxxxxxxxx> > >> > >> --- > >> fs/aio.c | 319 ++++++++++++++++++++++++++++++++++++++++++- > >> fs/buffer.c | 26 ++++- > >> fs/mpage.c | 28 ++++- > >> include/linux/aio.h | 9 ++ > >> include/linux/aio_abi.h | 1 + > >> include/linux/blk_types.h | 2 + > >> include/linux/buffer_head.h | 3 + > >> include/linux/page-flags.h | 2 + > >> include/linux/sched.h | 1 + > >> 9 files changed, 386 insertions(+), 5 deletions(-) > >> > > > > Hmm, I don't see the usage from user space. Is it possible to post a demo code in user space, so people are able to > > understand how to use/test your patch. > > He added a new IOCB_CMD_blah for buffered aio reads. That is, > unfortunately, a really poor way to go about doing things. Please take > a look at the work Jens did on implementing buffered aio. It can be > found in his linux-block git tree. Interesting, I thought Jens's work is to make io_submit not blocking. That's good to know it supports async buffer io too. Last time I look at the code, it appears there still are threads to do the aio retry, so what's the difference just letting user space thread do a sync buffer io? -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
