On Wed, Dec 16, 2015 at 10:19:00AM +0800, Qu Wenruo wrote: > > > Liu Bo wrote on 2015/12/15 17:53 -0800: > >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? > > Oh, it seems that I remembered the wrong size. > After checking the code, yes you're right. > A stripe won't be larger than 1G, so my assumption above is totally wrong. > > And the problem is not in the 10% limit. > > Please forget it.
No problem, glad to see people talking about the space issue again. Thanks, -liubo > > Thanks, > Qu > > > > > > >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
