From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cn.fujitsu.com ([59.151.112.132]:43445 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1756762AbaJ3A6K convert rfc822-to-8bit (ORCPT ); Wed, 29 Oct 2014 20:58:10 -0400 Message-ID: <54518D1F.9040008@cn.fujitsu.com> Date: Thu, 30 Oct 2014 08:58:07 +0800 From: Qu Wenruo MIME-Version: 1.0 To: CC: Subject: Re: [PATCH] btrfs: Enhance btrfs chunk allocation algorithm to reduce ENOSPC caused by unbalanced data/metadata allocation. References: <1414031871-10859-1-git-send-email-quwenruo@cn.fujitsu.com> <20141024110624.GB32526@localhost.localdomain> <544D8F44.8050706@cn.fujitsu.com> <20141027081456.GD27271@localhost.localdomain> <544E040A.3090407@cn.fujitsu.com> <20141029142917.GA9547@localhost.localdomain> In-Reply-To: <20141029142917.GA9547@localhost.localdomain> Content-Type: text/plain; charset="utf-8"; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: -------- Original Message -------- Subject: Re: [PATCH] btrfs: Enhance btrfs chunk allocation algorithm to reduce ENOSPC caused by unbalanced data/metadata allocation. From: Liu Bo To: Qu Wenruo Date: 2014年10月29日 22:29 > On Mon, Oct 27, 2014 at 04:36:26PM +0800, Qu Wenruo wrote: >> -------- Original Message -------- >> Subject: Re: [PATCH] btrfs: Enhance btrfs chunk allocation algorithm >> to reduce ENOSPC caused by unbalanced data/metadata allocation. >> From: Liu Bo >> To: Qu Wenruo >> Date: 2014年10月27日 16:14 >>> On Mon, Oct 27, 2014 at 08:18:12AM +0800, Qu Wenruo wrote: >>>> -------- Original Message -------- >>>> Subject: Re: [PATCH] btrfs: Enhance btrfs chunk allocation algorithm >>>> to reduce ENOSPC caused by unbalanced data/metadata allocation. >>>> From: Liu Bo >>>> To: Qu Wenruo >>>> Date: 2014年10月24日 19:06 >>>>> On Thu, Oct 23, 2014 at 10:37:51AM +0800, Qu Wenruo wrote: >>>>>> When btrfs allocate a chunk, it will try to alloc up to 1G for data and >>>>>> 256M for metadata, or 10% of all the writeable space if there is enough >>>>> 10G for data, >>>>> if (type & BTRFS_BLOCK_GROUP_DATA) { >>>>> max_stripe_size = 1024 * 1024 * 1024; >>>>> max_chunk_size = 10 * max_stripe_size; >>>> Oh, sorry, 10G is right. >>>> >>>> Any other comments? >>>> >>>> Thanks, >>>> Qu >>>> >>>> >>>>> ... >>>>> >>>>> thanks, >>>>> -liubo >>>>> >>>>>> space for the stripe on device. >>>>>> >>>>>> However, when we run out of space, this allocation may cause unbalanced >>>>>> chunk allocation. >>>>>> For example, there are only 1G unallocated space, and request for >>>>>> allocate DATA chunk is sent, and all the space will be allocated as data >>>>>> chunk, making later metadata chunk alloc request unable to handle, which >>>>>> will cause ENOSPC. >>>>>> This is the one of the common complains from end users about why ENOSPC >>>>>> happens but there is still available space. >>> Okay, I don't think this is the common case, AFAIK, the most ENOSPC is caused >>> by our runtime worst case metadata reservation problem. >>> >>> btrfs has been inclined to create a fairly large metadata chunk (1G) in its >>> initial mkfs stage and 256M metadata chunk is also a very large one. >>> >>> As of your below example, yes, we don't have space for metadata >>> allocation, but do we really need to allocate a new one? >>> >>> Or am I missing something? >>> >>> thanks, >>> -liubo >> Yes that's true this is not the common cause, but at least this >> patch may make the percentage >> of 'df' command reach as close to 100% as possible before hitting >> ENOSPC under normal operations. >> (If not using balance) >> >> And some case like the following mail may be improved by the patch: >> https://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg36097.html >> >> I understand that most of the cases that a lot of free data space >> and no metadata space is caused by >> create and then delete large files, but if the last giga bytes can >> be allocated more carefully, >> at least the available bytes of 'df' command should be reduced >> before hit ENOSPC. >> >> How do you think about it? > Sorry for the late reply. > > I just notice that a recent commit has fixed this problem. > > commit 47ab2a6c689913db23ccae38349714edf8365e0a > Author: Josef Bacik > Date: Thu Sep 18 11:20:02 2014 -0400 > > Btrfs: remove empty block groups automatically > > thanks, > -liubo Oh, that's much better than my patch. So please ignore my patch. Thanks, Qu > >> Thanks, >> Qu >>>>>> This patch will try not to alloc chunk which is more than half of the >>>>>> unallocated space, making the last space more balanced at a small cost >>>>>> of more fragmented chunk at the last 1G. >>>>>> >>>>>> Some easy example: >>>>>> Preallocate 17.5G on a 20G empty btrfs fs: >>>>>> [Before] >>>>>> # btrfs fi show /mnt/test >>>>>> Label: none uuid: da8741b1-5d47-4245-9e94-bfccea34e91e >>>>>> Total devices 1 FS bytes used 17.50GiB >>>>>> devid 1 size 20.00GiB used 20.00GiB path /dev/sdb >>>>>> All space is allocated. No space later metadata space. >>>>>> >>>>>> [After] >>>>>> # btrfs fi show /mnt/test >>>>>> Label: none uuid: e6935aeb-a232-4140-84f9-80aab1f23d56 >>>>>> Total devices 1 FS bytes used 17.50GiB >>>>>> devid 1 size 20.00GiB used 19.77GiB path /dev/sdb >>>>>> About 230M is still available for later metadata allocation. >>>>>> >>>>>> Signed-off-by: Qu Wenruo >>>>>> --- >>>>>> fs/btrfs/volumes.c | 18 ++++++++++++++++++ >>>>>> 1 file changed, 18 insertions(+) >>>>>> >>>>>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c >>>>>> index d47289c..fa8de79 100644 >>>>>> --- a/fs/btrfs/volumes.c >>>>>> +++ b/fs/btrfs/volumes.c >>>>>> @@ -4240,6 +4240,7 @@ static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans, >>>>>> int ret; >>>>>> u64 max_stripe_size; >>>>>> u64 max_chunk_size; >>>>>> + u64 total_avail_space = 0; >>>>>> u64 stripe_size; >>>>>> u64 num_bytes; >>>>>> u64 raid_stripe_len = BTRFS_STRIPE_LEN; >>>>>> @@ -4352,10 +4353,27 @@ static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans, >>>>>> devices_info[ndevs].max_avail = max_avail; >>>>>> devices_info[ndevs].total_avail = total_avail; >>>>>> devices_info[ndevs].dev = device; >>>>>> + total_avail_space += total_avail; >>>>>> ++ndevs; >>>>>> } >>>>>> /* >>>>>> + * Try not to occupy more than half of the unallocated space. >>>>>> + * When run short of space and alloc all the space to >>>>>> + * data/metadata will cause ENOSPC to be triggered more easily. >>>>>> + * >>>>>> + * And since the minimum chunk size is 16M, the half-half will cause >>>>>> + * 16M allocated from 20M available space and reset 4M will not be >>>>>> + * used ever. In that case(16~32M), allocate all directly. >>>>>> + */ >>>>>> + if (total_avail_space < 32 * 1024 * 1024 && >>>>>> + total_avail_space > 16 * 1024 * 1024) >>>>>> + max_chunk_size = total_avail_space; >>>>>> + else >>>>>> + max_chunk_size = min(total_avail_space / 2, max_chunk_size); >>>>>> + max_chunk_size = min(total_avail_space / 2, max_chunk_size); >>>>>> + >>>>>> + /* >>>>>> * now sort the devices by hole size / available space >>>>>> */ >>>>>> sort(devices_info, ndevs, sizeof(struct btrfs_device_info), >>>>>> -- >>>>>> 2.1.2 >>>>>> >>>>>> -- >>>>>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in >>>>>> the body of a message to majordomo@vger.kernel.org >>>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html