From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 772A2C43381 for ; Wed, 27 Feb 2019 19:42:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2DCE62186A for ; Wed, 27 Feb 2019 19:42:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="CyGRAurS" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730136AbfB0Tmp (ORCPT ); Wed, 27 Feb 2019 14:42:45 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:49664 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727240AbfB0Tmp (ORCPT ); Wed, 27 Feb 2019 14:42:45 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=WOc30ZfcIOdbeK1wHHws4Nf+FbdsM2peacdGwXkl0uw=; b=CyGRAurSMclDoLdadl8spglRM +r1d0W8wn8NPupF8/wT/y0WhAXY6Aw1MV5WZ2GN6duM4tqBVgWiynCGl3AuYNlrrCNnD1K0wK2qsv +VXRa4VjxUISsnLVXPaOxwizsvuSRFR+qP+2YTSOB/ATcr/EX3a1WjkKNEHo02acZGUMw//jZaqDk WsvVMbaVA76PaYvYdwYgG2I1HsPkVZNCaOTdZG/BvygxfI21J0ABRUe07sSdt3dzEBSYaAuV1vo/+ WTBm3qN9OvPi6s+sMHJ5Yq2WCOq14lnVvqxdwpGVnjJOSgJ0xCHdayPpdH/IxPdpIVUmOIXaXlsAC X6Yulj45g==; Received: from hch by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1gz56H-0002Os-7n; Wed, 27 Feb 2019 19:42:41 +0000 Date: Wed, 27 Feb 2019 11:42:41 -0800 From: Christoph Hellwig To: Jens Axboe Cc: Ming Lei , Ming Lei , Eric Biggers , "open list:AIO" , linux-block , linux-api@vger.kernel.org, Christoph Hellwig , Jeff Moyer , Avi Kivity , jannh@google.com, Al Viro Subject: Re: [PATCH 11/19] block: implement bio helper to add iter bvec pages to bio Message-ID: <20190227194241.GA3860@infradead.org> References: <20190227022144.GE16802@ming.t460p> <20190227023719.GF16802@ming.t460p> <9ce37f86-dd8b-ef51-7507-d457585a892a@kernel.dk> <20190227030944.GG16802@ming.t460p> <7a1f4293-8f88-81e0-9464-cc27e39184cb@kernel.dk> <20190227034409.GH16802@ming.t460p> <2a48c5da-7eea-13a1-9939-9e182e11dc9b@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.2 (2017-12-15) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Tue, Feb 26, 2019 at 09:06:23PM -0700, Jens Axboe wrote: > On 2/26/19 9:05 PM, Jens Axboe wrote: > > On 2/26/19 8:44 PM, Ming Lei wrote: > >> On Tue, Feb 26, 2019 at 08:37:05PM -0700, Jens Axboe wrote: > >>> On 2/26/19 8:09 PM, Ming Lei wrote: > >>>> On Tue, Feb 26, 2019 at 07:43:32PM -0700, Jens Axboe wrote: > >>>>> On 2/26/19 7:37 PM, Ming Lei wrote: > >>>>>> On Tue, Feb 26, 2019 at 07:28:54PM -0700, Jens Axboe wrote: > >>>>>>> On 2/26/19 7:21 PM, Ming Lei wrote: > >>>>>>>> On Tue, Feb 26, 2019 at 06:57:16PM -0700, Jens Axboe wrote: > >>>>>>>>> On 2/26/19 6:53 PM, Ming Lei wrote: > >>>>>>>>>> On Tue, Feb 26, 2019 at 06:47:54PM -0700, Jens Axboe wrote: > >>>>>>>>>>> On 2/26/19 6:21 PM, Ming Lei wrote: > >>>>>>>>>>>> On Tue, Feb 26, 2019 at 11:56 PM Jens Axboe wrote: > >>>>>>>>>>>>> > >>>>>>>>>>>>> On 2/25/19 9:34 PM, Jens Axboe wrote: > >>>>>>>>>>>>>> On 2/25/19 8:46 PM, Eric Biggers wrote: > >>>>>>>>>>>>>>> Hi Jens, > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> On Thu, Feb 21, 2019 at 10:45:27AM -0700, Jens Axboe wrote: > >>>>>>>>>>>>>>>> On 2/20/19 3:58 PM, Ming Lei wrote: > >>>>>>>>>>>>>>>>> On Mon, Feb 11, 2019 at 12:00:41PM -0700, Jens Axboe wrote: > >>>>>>>>>>>>>>>>>> For an ITER_BVEC, we can just iterate the iov and add the pages > >>>>>>>>>>>>>>>>>> to the bio directly. This requires that the caller doesn't releases > >>>>>>>>>>>>>>>>>> the pages on IO completion, we add a BIO_NO_PAGE_REF flag for that. > >>>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>>> The current two callers of bio_iov_iter_get_pages() are updated to > >>>>>>>>>>>>>>>>>> check if they need to release pages on completion. This makes them > >>>>>>>>>>>>>>>>>> work with bvecs that contain kernel mapped pages already. > >>>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>>> Reviewed-by: Hannes Reinecke > >>>>>>>>>>>>>>>>>> Reviewed-by: Christoph Hellwig > >>>>>>>>>>>>>>>>>> Signed-off-by: Jens Axboe > >>>>>>>>>>>>>>>>>> --- > >>>>>>>>>>>>>>>>>> block/bio.c | 59 ++++++++++++++++++++++++++++++++------- > >>>>>>>>>>>>>>>>>> fs/block_dev.c | 5 ++-- > >>>>>>>>>>>>>>>>>> fs/iomap.c | 5 ++-- > >>>>>>>>>>>>>>>>>> include/linux/blk_types.h | 1 + > >>>>>>>>>>>>>>>>>> 4 files changed, 56 insertions(+), 14 deletions(-) > >>>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>>> diff --git a/block/bio.c b/block/bio.c > >>>>>>>>>>>>>>>>>> index 4db1008309ed..330df572cfb8 100644 > >>>>>>>>>>>>>>>>>> --- a/block/bio.c > >>>>>>>>>>>>>>>>>> +++ b/block/bio.c > >>>>>>>>>>>>>>>>>> @@ -828,6 +828,23 @@ int bio_add_page(struct bio *bio, struct page *page, > >>>>>>>>>>>>>>>>>> } > >>>>>>>>>>>>>>>>>> EXPORT_SYMBOL(bio_add_page); > >>>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>>> +static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter) > >>>>>>>>>>>>>>>>>> +{ > >>>>>>>>>>>>>>>>>> + const struct bio_vec *bv = iter->bvec; > >>>>>>>>>>>>>>>>>> + unsigned int len; > >>>>>>>>>>>>>>>>>> + size_t size; > >>>>>>>>>>>>>>>>>> + > >>>>>>>>>>>>>>>>>> + len = min_t(size_t, bv->bv_len, iter->count); > >>>>>>>>>>>>>>>>>> + size = bio_add_page(bio, bv->bv_page, len, > >>>>>>>>>>>>>>>>>> + bv->bv_offset + iter->iov_offset); > >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> iter->iov_offset needs to be subtracted from 'len', looks > >>>>>>>>>>>>>>>>> the following delta change[1] is required, otherwise memory corruption > >>>>>>>>>>>>>>>>> can be observed when running xfstests over loop/dio. > >>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>> Thanks, I folded this in. > >>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>> -- > >>>>>>>>>>>>>>>> Jens Axboe > >>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> syzkaller started hitting a crash on linux-next starting with this commit, and > >>>>>>>>>>>>>>> it still occurs even with your latest version that has Ming's fix folded in. > >>>>>>>>>>>>>>> Specifically, commit a566653ab5ab80a from your io_uring branch with commit date > >>>>>>>>>>>>>>> Sun Feb 24 08:20:53 2019 -0700. > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> Reproducer: > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> #define _GNU_SOURCE > >>>>>>>>>>>>>>> #include > >>>>>>>>>>>>>>> #include > >>>>>>>>>>>>>>> #include > >>>>>>>>>>>>>>> #include > >>>>>>>>>>>>>>> #include > >>>>>>>>>>>>>>> #include > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> int main(void) > >>>>>>>>>>>>>>> { > >>>>>>>>>>>>>>> int memfd, loopfd; > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> memfd = syscall(__NR_memfd_create, "foo", 0); > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> pwrite(memfd, "\xa8", 1, 4096); > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> loopfd = open("/dev/loop0", O_RDWR|O_DIRECT); > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> ioctl(loopfd, LOOP_SET_FD, memfd); > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> sendfile(loopfd, loopfd, NULL, 1000000); > >>>>>>>>>>>>>>> } > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> Crash: > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> page:ffffea0001a6aab8 count:0 mapcount:0 mapping:0000000000000000 index:0x0 > >>>>>>>>>>>>>>> flags: 0x100000000000000() > >>>>>>>>>>>>>>> raw: 0100000000000000 ffffea0001ad2c50 ffff88807fca49d0 0000000000000000 > >>>>>>>>>>>>>>> raw: 0000000000000000 0000000000000000 00000000ffffffff > >>>>>>>>>>>>>>> page dumped because: VM_BUG_ON_PAGE(page_ref_count(page) == 0) > >>>>>>>>>>>>>> > >>>>>>>>>>>>>> I see what this is, I'll cut a fix for this tomorrow. > >>>>>>>>>>>>> > >>>>>>>>>>>>> Folded in a fix for this, it's in my current io_uring branch and my for-next > >>>>>>>>>>>>> branch. > >>>>>>>>>>>> > >>>>>>>>>>>> Hi Jens, > >>>>>>>>>>>> > >>>>>>>>>>>> I saw the following change is added: > >>>>>>>>>>>> > >>>>>>>>>>>> + if (size == len) { > >>>>>>>>>>>> + /* > >>>>>>>>>>>> + * For the normal O_DIRECT case, we could skip grabbing this > >>>>>>>>>>>> + * reference and then not have to put them again when IO > >>>>>>>>>>>> + * completes. But this breaks some in-kernel users, like > >>>>>>>>>>>> + * splicing to/from a loop device, where we release the pipe > >>>>>>>>>>>> + * pages unconditionally. If we can fix that case, we can > >>>>>>>>>>>> + * get rid of the get here and the need to call > >>>>>>>>>>>> + * bio_release_pages() at IO completion time. > >>>>>>>>>>>> + */ > >>>>>>>>>>>> + get_page(bv->bv_page); > >>>>>>>>>>>> > >>>>>>>>>>>> Now the 'bv' may point to more than one page, so the following one may be > >>>>>>>>>>>> needed: > >>>>>>>>>>>> > >>>>>>>>>>>> int i; > >>>>>>>>>>>> struct bvec_iter_all iter_all; > >>>>>>>>>>>> struct bio_vec *tmp; > >>>>>>>>>>>> > >>>>>>>>>>>> mp_bvec_for_each_segment(tmp, bv, i, iter_all) > >>>>>>>>>>>> get_page(tmp->bv_page); > >>>>>>>>>>> > >>>>>>>>>>> I guess that would be the safest, even if we don't currently have more > >>>>>>>>>>> than one page in there. I'll fix it up. > >>>>>>>>>> > >>>>>>>>>> It is easy to see multipage bvec from loop, :-) > >>>>>>>>> > >>>>>>>>> Speaking of this, I took a quick look at why we've now regressed a lot > >>>>>>>>> on IOPS perf with the multipage work. It looks like it's all related to > >>>>>>>>> the (much) fatter setup around iteration, which is related to this very > >>>>>>>>> topic too. > >>>>>>>>> > >>>>>>>>> Basically setup of things like bio_for_each_bvec() and indexing through > >>>>>>>>> nth_page() is MUCH slower than before. > >>>>>>>> > >>>>>>>> But bio_for_each_bvec() needn't nth_page(), and only bio_for_each_segment() > >>>>>>>> needs that. However, bio_for_each_segment() isn't called from > >>>>>>>> blk_queue_split() and blk_rq_map_sg(). > >>>>>>>> > >>>>>>>> One issue is that bio_for_each_bvec() still advances by page size > >>>>>>>> instead of bvec->len, I guess that is the problem, will cook a patch > >>>>>>>> for your test. > >>>>>>> > >>>>>>> Probably won't make a difference for my test case... > >>>>>>> > >>>>>>>>> We need to do something about this, it's like tossing out months of > >>>>>>>>> optimizations. > >>>>>>>> > >>>>>>>> Some following optimization can be done, such as removing > >>>>>>>> biovec_phys_mergeable() from blk_bio_segment_split(). > >>>>>>> > >>>>>>> I think we really need a fast path for <= PAGE_SIZE IOs, to the extent > >>>>>>> that it is possible. But iteration startup cost is a problem in a lot of > >>>>>>> spots, and a split fast path will only help a bit for that specific > >>>>>>> case. > >>>>>>> > >>>>>>> 5% regressions is HUGE. I know I've mentioned this before, I just want > >>>>>>> to really stress how big of a deal that is. It's enough to make me > >>>>>>> consider just reverting it again, which sucks, but I don't feel great > >>>>>>> shipping something that is known that much slower. > >>>>>>> > >>>>>>> Suggestions? > >>>>>> > >>>>>> You mentioned nth_page() costs much in bio_for_each_bvec(), but which > >>>>>> shouldn't call into nth_page(). I will look into it first. > >>>>> > >>>>> I'll check on the test box tomorrow, I lost connectivity before. I'll > >>>>> double check in the morning. > >>>>> > >>>>> I'd focus on the blk_rq_map_sg() path, since that's the biggest cycle > >>>>> consumer. > >>>> > >>>> Hi Jens, > >>>> > >>>> Could you test the following patch which may improve on the 4k randio > >>>> test case? > >>> > >>> A bit, it's up 1% with this patch. I'm going to try without the > >>> get_page/put_page that we had earlier, to see where we are in regards to > >>> the old baseline. > >> > >> OK, today I will test io_uring over null_blk on one real machine and see > >> if something can be improved. > > > > For reference, I'm running the default t/io_uring from fio, which is > > QD=128, fixed files/buffers, and polled. Running it on two devices to > > max out the CPU core: > > > > sudo taskset -c 0 t/io_uring /dev/nvme1n1 /dev/nvme5n1 > > Forgot to mention, this is loading nvme with 12 poll queues, which is of > course important to get good performance on this test case. Btw, is your nvme device SGL capable? There is some low hanging fruit in that IFF a device has SGL support we can basically dumb down blk_mq_map_sg to never split in this case ever because we don't have any segment size limits. PRPs only unforturtunately are a little dumb and could lead to all kinds of whacky splitting.