At Mon, 1 Oct 2012 13:53:55 +0100, Chris Webb wrote: > > MORITA Kazutaka <morita.kazut...@lab.ntt.co.jp> writes: > > > Chris Webb wrote: > > > > > > I remember that loopback iscsi and nbd are very prone to deadlock under > > > memory pressure, because more dirty pages need to be created to be able to > > > progress with writing out the existing ones. Presumably a kernel sheepdog > > > driver would suffer from the same problem, and it would be very hard to > > > enable sheepdog hosts to mount filesystems on a cluster of which they're a > > > part? > > > > Probably, the answer is yes... I thought that it would be nice to > > access a sheepdog gateway on localhost with an iSCSI protocol, but it > > would lead to the deadlock problem. > [...] > > Seems that Ceph suffers from the same problem: > > http://tracker.newdream.net/issues/3076 > > I wonder whether memory cgroups will eventually provide a mechanism that can > help here. Perhaps a restricted container on the host could safely access > the sheepdog-backed block device because it is constrained by memcg to never > be able to dirty enough pages that the host is unable to make progress. > Private filesystem namespaces could be used to explicitly ensure the mount > isn't accidentally touched outside the memcg restriction.
So sheeps can allocate memory without flushing pagecache of sheepdog VDIs? Sounds like a reasonable way to cope with this problem. Thanks, Kazutaka -- sheepdog mailing list sheepdog@lists.wpkg.org http://lists.wpkg.org/mailman/listinfo/sheepdog
