[RFC PATCH 0/2] NFSD: Rate-limiting unstable WRITEs

[Chuck Lever <cel@kernel.org>]

From: Chuck Lever <chuck.lever@oracle.com>

Following up on

  https://lore.kernel.org/linux-nfs/99dd427d-a16e-4494-a4b1-ff65488181ee@oracle.com/

Client workloads that are write-intensive can sometimes trigger an
NFSD meltdown (thrashing, livelocking, or becoming unresponsive).
This can happen when clients present NFSD with more UNSTABLE WRITEs
than can fit in the server's physical memory, and the system simply
can't get those dirty pages onto persistent storage fast enough.

In those cases, it makes sense to slow those clients down until the
backlog can be cleared out. NFSD might do this by delaying the
responses to UNSTABLE WRITEs, which in turn leaves unprocessed
ingress WRITEs on the transport queue longer, and thus closes down
the ingress congestion window on the network connection. This
applies direct backpressure on the noisy clients.

NFSD might already be doing this to some extent, but it can be
argued that it is not going far enough.

These two patches fall squarely in the "crazy ideas" category, but
I hope they serve as conversation starters.

Chuck Lever (2):
  NFSD: Add aggressive write throttling control
  NFSD: Add asynchronous write throttling support

 fs/nfsd/debugfs.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++
 fs/nfsd/nfsd.h    | 10 +++++++
 fs/nfsd/vfs.c     | 34 ++++++++++++++++++++++++
 3 files changed, 111 insertions(+)

-- 
2.52.0