On Wed, Dec 16, 2015 at 09:20:45AM +0800, Qu Wenruo wrote: > > > Chris Mason wrote on 2015/12/15 16:59 -0500: > >On Mon, Dec 14, 2015 at 10:08:16AM +0800, Qu Wenruo wrote: > >> > >> > >>Martin Steigerwald wrote on 2015/12/13 23:35 +0100: > >>>Hi! > >>> > >>>For me it is still not production ready. > >> > >>Yes, this is the *FACT* and not everyone has a good reason to deny it. > >> > >>>Again I ran into: > >>> > >>>btrfs kworker thread uses up 100% of a Sandybridge core for minutes on > >>>random > >>>write into big file > >>>https://bugzilla.kernel.org/show_bug.cgi?id=90401 > >> > >>Not sure about guideline for other fs, but it will attract more dev's > >>attention if it can be posted to maillist. > >> > >>> > >>> > >>>No matter whether SLES 12 uses it as default for root, no matter whether > >>>Fujitsu and Facebook use it: I will not let this onto any customer machine > >>>without lots and lots of underprovisioning and rigorous free space > >>>monitoring. > >>>Actually I will renew my recommendations in my trainings to be careful with > >>>BTRFS. > >>> > >>> From my experience the monitoring would check for: > >>> > >>>merkaba:~> btrfs fi show /home > >>>Label: 'home' uuid: […] > >>> Total devices 2 FS bytes used 156.31GiB > >>> devid 1 size 170.00GiB used 164.13GiB path > >>> /dev/mapper/msata-home > >>> devid 2 size 170.00GiB used 164.13GiB path > >>> /dev/mapper/sata-home > >>> > >>>If "used" is same as "size" then make big fat alarm. It is not sufficient > >>>for > >>>it to happen. It can run for quite some time just fine without any issues, > >>>but > >>>I never have seen a kworker thread using 100% of one core for extended > >>>period > >>>of time blocking everything else on the fs without this condition being > >>>met. > >>> > >> > >>And specially advice on the device size from myself: > >>Don't use devices over 100G but less than 500G. > >>Over 100G will leads btrfs to use big chunks, where data chunks can be at > >>most 10G and metadata to be 1G. > >> > >>I have seen a lot of users with about 100~200G device, and hit unbalanced > >>chunk allocation (10G data chunk easily takes the last available space and > >>makes later metadata no where to store) > > > >Maybe we should tune things so the size of the chunk is based on the > >space remaining instead of the total space? > > Submitted such patch before. > David pointed out that such behavior will cause a lot of small fragmented > chunks at last several GB. > Which may make balance behavior not as predictable as before. > > > At least, we can just change the current 10% chunk size limit to 5% to make > such problem less easier to trigger. > It's a simple and easy solution. > > Another cause of the problem is, we understated the chunk size change for fs > at the borderline of big chunk. > > For 99G, its chunk size limit is 1G, and it needs 99 data chunks to fully > cover the fs. > But for 100G, it only needs 10 chunks to covert the fs. > And it need to be 990G to match the number again.
max_stripe_size is fixed at 1GB and the chunk size is stripe_size * data_stripes, may I know how your partition gets a 10GB chunk? Thanks, -liubo > > The sudden drop of chunk number is the root cause. > > So we'd better reconsider both the big chunk size limit and chunk size limit > to find a balanaced solution for it. > > Thanks, > Qu > > > >> > >>And unfortunately, your fs is already in the dangerous zone. > >>(And you are using RAID1, which means it's the same as one 170G btrfs with > >>SINGLE data/meta) > >> > >>> > >>>In addition to that last time I tried it aborts scrub any of my BTRFS > >>>filesstems. Reported in another thread here that got completely ignored so > >>>far. I think I could go back to 4.2 kernel to make this work. > > > >We'll pick this thread up again, the ones that get fixed the fastest are > >the ones that we can easily reproduce. The rest need a lot of think > >time. > > > >-chris > > > > > > > -- > 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
