On Fri, Aug 28, 2015 at 3:31 AM, Josh Durgin <jdur...@redhat.com> wrote: > On 08/27/2015 09:49 AM, Stefan Hajnoczi wrote: >> >> On Mon, Aug 25, 2014 at 03:50:02PM -0600, Chris Friesen wrote: >>> >>> The only limit I see in the whole call chain from >>> virtio_blk_handle_request() on down is the call to >>> bdrv_io_limits_intercept() in bdrv_co_do_writev(). However, that doesn't >>> provide any limit on the absolute number of inflight operations, only on >>> operations/sec. If the ceph server cluster can't keep up with the >>> aggregate >>> load, then the number of inflight operations can still grow indefinitely. >> >> >> We probably shouldn't rely on QEMU I/O throttling to keep memory usage >> reasonable. > > > Agreed. > >> Instead rbd should be adjusted to support iovecs as you suggested. That >> way no bounce buffers are needed. > > > Yeah, this is pretty simple to do. Internally librbd has iovec-equivalents. > I'm not sure this is the main source of extra memory usage > though. > > I suspect the main culprit here is rbd cache letting itself burst too > large, rather than the bounce buffers. > > Andrey, does this still occur with caching off?
No, complete cache disablement helped so far perfectly, what cannot be said for wt/wb modes. As I mentioned, the consumption curve is a reactive by its nature, so I`ll try to catch the burst under valgrind but cannot promise anything.
