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 <bo.li....@oracle.com> > To: Qu Wenruo <quwen...@cn.fujitsu.com> > 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 <bo.li....@oracle.com> > >>To: Qu Wenruo <quwen...@cn.fujitsu.com> > >>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 <jba...@fb.com> Date: Thu Sep 18 11:20:02 2014 -0400 Btrfs: remove empty block groups automatically thanks, -liubo > > 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 <quwen...@cn.fujitsu.com> > >>>>--- > >>>> 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 majord...@vger.kernel.org > >>>>More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html