From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Moyer Subject: Re: [PATCH][RFC] A readahead complete notify approach to implement buffer aio Date: Thu, 03 Nov 2011 14:01:55 -0400 Message-ID: References: <1320138024-10837-1-git-send-email-gaoyang.zyh@taobao.com> <4EB2D8CF.2080108@coly.li> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Cc: Zhu Yanhai , linux-kernel@vger.kernel.org, bcrl@kvack.org, viro@zeniv.linux.org.uk, linux-aio@kvack.org, linux-fsdevel@vger.kernel.org, jaxboe@fusionio.com, Zhu Yanhai To: i@coly.li Return-path: In-Reply-To: <4EB2D8CF.2080108@coly.li> (Coly Li's message of "Fri, 04 Nov 2011 02:09:19 +0800") Sender: owner-linux-aio@kvack.org List-Id: linux-fsdevel.vger.kernel.org Coly Li writes: > On 2011=E5=B9=B411=E6=9C=8801=E6=97=A5 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 we= re reclaimed >> between io_submit() and io_getevents(). >>=20 >> I have tested this patch for a while, for the small size random io reque= st, its >> performance is more or less the same with the traditional aio, for the b= ig io request, >> the overhead of one extra memory copy arises. >>=20 >> I think so far it has at least below obvious drawbacks, >>=20 >> * mpage_readpage() is a really narrow interface, I have no way to pass d= own >> the new control struct baiocb, so I just put it into struct task_struct = and >> refer it by current() as a workaround. >>=20 >> * the do_baio_read() routine is heavily similar with do_generic_file_rea= d(), but >> the latter is really hard to modify. I think we may stuff these code dow= n into the >> readahead path to reduce code reduplication. >>=20 >> Hopefully the explanations are clear enough and don't muddy the water an= y worse. >> I figure the code does need some better comments, and any suggestion are= welcome. >>=20 >> Signed-off-by: Zhu Yanhai >>=20 >> --- >> 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(-) >>=20 > > 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. Cheers, Jeff -- To unsubscribe, send a message with 'unsubscribe linux-aio' in the body to majordomo@kvack.org. For more info on Linux AIO, see: http://www.kvack.org/aio/ Don't email: aart@kvack.org