On 10/24/22 1:05 PM, Stefan Roesch wrote: > At meta network block devices (nbd) are used to implement remote block > storage. In testing and during production it has been observed that > these network block devices can consume a huge portion of the dirty > writeback cache and writeback can take a considerable time. > > To be able to give stricter limits, I'm proposing the following changes: > > 1) introduce strictlimit knob > > Currently the max_ratio knob exists to limit the dirty_memory. However > this knob only applies once (dirty_ratio + dirty_background_ratio) / 2 > has been reached. > With the BDI_CAP_STRICTLIMIT flag, the max_ratio can be applied without > reaching that limit. This change exposes that knob. > > This knob can also be useful for NFS, fuse filesystems and USB devices. > > 2) Use part of 1000 internal calculation > > The max_ratio is based on percentage. With the current machine sizes > percentage values can be very high (1% of a 256GB main memory is already > 2.5GB). This change uses part of 1000 instead of percentages for the > internal calculations. > > 3) Introduce two new sysfs knobs: min_bytes and max_bytes. > > Currently all calculations are based on ratio, but for a user it often > more convenient to specify a limit in bytes. The new knobs will not > store bytes values, instead they will translate the byte value to a > corresponding ratio. As the internal values are now part of 1000, the > ratio is closer to the specified value. However the value should be more > seen as an approximation as it can fluctuate over time. Anyone have any concerns or input on this series? Would be nice to get it moving forward, as we do have a need for it at Meta. Outside of that, would be applicable for end-user use cases as well on the distro side. -- Jens Axboe
