On Tue, Aug 28, 2012 at 12:07 PM, Alan Cox <[email protected]> wrote: > On 08/27/2012 17:23, Gezeala M. Bacuño II wrote: >> >> On Thu, Aug 23, 2012 at 12:02 PM, Alan Cox<[email protected]> wrote: >>> >>> On 08/22/2012 12:09, Gezeala M. Bacuño II wrote: >>>> >>>> On Tue, Aug 21, 2012 at 4:24 PM, Alan Cox<[email protected]> wrote: >>>>> >>>>> On 8/20/2012 8:26 PM, Gezeala M. Bacuño II wrote: >>>>>> >>>>>> On Mon, Aug 20, 2012 at 9:07 AM, Gezeala M. Bacuño >>>>>> II<[email protected]> >>>>>> wrote: >>>>>>> >>>>>>> On Mon, Aug 20, 2012 at 8:22 AM, Alan Cox<[email protected]> wrote: >>>>>>>> >>>>>>>> On 08/18/2012 19:57, Gezeala M. Bacuño II wrote: >>>>>>>>> >>>>>>>>> On Sat, Aug 18, 2012 at 12:14 PM, Alan Cox<[email protected]> wrote: >>>>>>>>>> >>>>>>>>>> On 08/17/2012 17:08, Gezeala M. Bacuño II wrote: >>>>>>>>>>> >>>>>>>>>>> On Fri, Aug 17, 2012 at 1:58 PM, Alan Cox<[email protected]> >>>>>>>>>>> wrote: >>>>>>>>>>>> >>>>>>>>>>>> vm.kmem_size controls the maximum size of the kernel's heap, >>>>>>>>>>>> i.e., >>>>>>>>>>>> the >>>>>>>>>>>> region where the kernel's slab and malloc()-like memory >>>>>>>>>>>> allocators >>>>>>>>>>>> obtain >>>>>>>>>>>> their memory. While this heap may occupy the largest portion of >>>>>>>>>>>> the >>>>>>>>>>>> kernel's virtual address space, it cannot occupy the entirety of >>>>>>>>>>>> the >>>>>>>>>>>> address >>>>>>>>>>>> space. There are other things that must be given space within >>>>>>>>>>>> the >>>>>>>>>>>> kernel's >>>>>>>>>>>> address space, for example, the file system buffer map. >>>>>>>>>>>> >>>>>>>>>>>> ZFS does not, however, use the regular file system buffer cache. >>>>>>>>>>>> The >>>>>>>>>>>> ARC >>>>>>>>>>>> takes its place, and the ARC abuses the kernel's heap like >>>>>>>>>>>> nothing >>>>>>>>>>>> else. >>>>>>>>>>>> So, if you are running a machine that only makes trivial use of >>>>>>>>>>>> a >>>>>>>>>>>> non-ZFS >>>>>>>>>>>> file system, like you boot from UFS, but store all of your data >>>>>>>>>>>> in >>>>>>>>>>>> ZFS, >>>>>>>>>>>> then >>>>>>>>>>>> you can dramatically reduce the size of the buffer map via boot >>>>>>>>>>>> loader >>>>>>>>>>>> tuneables and proportionately increase vm.kmem_size. >>>>>>>>>>>> >>>>>>>>>>>> Any further increases in the kernel virtual address space size >>>>>>>>>>>> will, >>>>>>>>>>>> however, require code changes. Small changes, but changes >>>>>>>>>>>> nonetheless. >>>>>>>>>>>> >>>>>>>>>>>> Alan >>>>>>>>>>>> >>>>>>> <<snip>> >>>>>>>>>> >>>>>>>>>> Your objective should be to reduce the value of "sysctl >>>>>>>>>> vfs.maxbufspace". >>>>>>>>>> You can do this by setting the loader.conf tuneable >>>>>>>>>> "kern.maxbcache" >>>>>>>>>> to >>>>>>>>>> the >>>>>>>>>> desired value. >>>>>>>>>> >>>>>>>>>> What does your machine currently report for "sysctl >>>>>>>>>> vfs.maxbufspace"? >>>>>>>>>> >>>>>>>>> Here you go: >>>>>>>>> vfs.maxbufspace: 54967025664 >>>>>>>>> kern.maxbcache: 0 >>>>>>>> >>>>>>>> >>>>>>>> Try setting kern.maxbcache to two billion and adding 50 billion to >>>>>>>> the >>>>>>>> setting of vm.kmem_size{,_max}. >>>>>>>> >>>>>> 2 : 50 ==>> is this the ratio for further tuning >>>>>> kern.maxbcache:vm.kmem_size? Is kern.maxbcache also in bytes? >>>>>> >>>>> No, this is not a ratio. Yes, kern.maxbcache is in bytes. Basically, >>>>> for >>>>> every byte that you subtract from vfs.maxbufspace, through setting >>>>> kern.maxbcache, you can add a byte to vm.kmem_size{,_max}. >>>>> >>>>> Alan >>>>> >>>> Great! Thanks. Are there other sysctls aside from vfs.bufspace that I >>>> should monitor for vfs.maxbufspace usage? I just want to make sure >>>> that vfs.maxbufspace is sufficient for our needs. >>> >>> >>> You might keep an eye on "sysctl vfs.bufdefragcnt". If it starts rapidly >>> increasing, you may want to increase vfs.maxbufspace. >>> >>> Alan >>> >> We seem to max out vfs.bufspace in<24hrs uptime. It has been steady >> at 1999273984 while vfs.bufdefragcnt stays at 0 - which I presume is >> good. Nevertheless, I will increase kern.maxbcache to 6GB and adjust >> vm.kmem_size{,_max}, vfs.zfs.arc_max accordingly. On another machine >> with vfs.maxbufspace auto-tuned to 7738671104 (~7.2GB), vfs.bufspace >> is now at 5278597120 (uptime 129 days). > > > The buffer map is a kind of cache. Like any cache, most of the time it will > be full. Don't worry. > > Moreover, even when the buffer map is full, the UFS file system is caching > additional file data in physical memory pages that simply aren't mapped for > instantaneous access. Essentially, limiting the size of the buffer map is > only limiting the amount of modified file data that hasn't been written back > to disk, not the total amount of cached data. > > As long as you're making trivial use of UFS file systems, there really isn't > a reason to increase the buffer map size. > > Alan > >
I see. Makes sense now. Thanks! I forgot to mention that we do have smbfs mounts mounted from another server, are writes/modifications on files on these mounts also cached in the buffer map? All non-ZFS file systems right? Input/Output files are read from or written to these mounts. _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-performance To unsubscribe, send any mail to "[email protected]"
