Please note I have not tested this version yet: I'm just putting it out for review. Mike On 01/02/2018 11:00 AM, Michael Lyle wrote: > This fixes bcache writeback target calculation, for defects relating to > large cache sets and calculation errors when there are multiple backing > devices. > > Bcache needs to scale the dirty data in the cache over the multiple > backing disks in order to calculate writeback rates for each. > The previous code did this by multiplying the target number of dirty > sectors by the backing device size, and expected it to fit into a > uint64_t; this blows up on relatively small backing devices. > > The new approach figures out the bdev's share in 16384ths of the overall > cached data. This is chosen to cope well when bdevs drastically vary in > size and to ensure that bcache can cross the petabyte boundary for each > backing device. > > Per review, we ensure that every device gets at least 1/16384th of the > writeback share. This also differs from v1 of the patchset in scaling > the error, which corrects previous problems with writeback rate > calculation across multiple devices. > > Reported-by: Jack Douglas <jack@xxxxxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Michael Lyle <mlyle@xxxxxxxx>
