[PATCH v4 0/7] Intruduce nfsrahead

[Thiago Becker <tbecker@redhat.com>]

Recent changes in the linux kernel caused NFS readahead to default to
128 from the previous default of 15 * rsize. This causes performance
penalties to some read-heavy workloads, which can be fixed by
tuning the readahead for that given mount.

Specifically, the read troughput on a sec=krb5p mount drops by 50-75%
when comparing the default readahead with a readahead of 15360.

Previous discussions:
https://lore.kernel.org/linux-nfs/20210803130717.2890565-1-trbecker@gmail.com/
I attempted to add a non-kernel option to mount.nfs, and it was
rejected.

https://lore.kernel.org/linux-nfs/20210811171402.947156-1-trbecker@gmail.com/
Attempted to add a mount option to the kernel, rejected as well.

I had started a separate tool to set the readahead of BDIs, but the
scope is specifically for NFS, so I would like to get the community
feeling for having this in nfs-utils.

This patch series introduces nfs-readahead-udev, a utility to
automatically set NFS readahead when NFS is mounted. The utility is
triggered by udev when a new BDI is added, returns to udev the value of
the readahead that should be used.

The tool currently supports setting read ahead per mountpoint, nfs major
version, or by a global default value.

v2:
    - explain the motivation

v3:
    - adopt already available facilities
    - nfsrahead is now configured in nfs.conf

v4:
    - retry getting the device if it fails
    - assorted fixes and improvements

Thiago Becker (7):
  Create nfsrahead
  nfsrahead: configure udev
  nfsrahead: only set readahead for nfs devices.
  nfsrahead: add logging
  nfsrahead: get the information from the config file.
  nfsrahead: User documentation
  nfsrahead: retry getting the device if it fails.

 .gitignore                      |   2 +
 configure.ac                    |   1 +
 systemd/nfs.conf.man            |  11 ++
 tools/Makefile.am               |   2 +-
 tools/nfsrahead/99-nfs.rules.in |   1 +
 tools/nfsrahead/Makefile.am     |  16 +++
 tools/nfsrahead/main.c          | 183 ++++++++++++++++++++++++++++++++
 tools/nfsrahead/nfsrahead.man   |  72 +++++++++++++
 8 files changed, 287 insertions(+), 1 deletion(-)
 create mode 100644 tools/nfsrahead/99-nfs.rules.in
 create mode 100644 tools/nfsrahead/Makefile.am
 create mode 100644 tools/nfsrahead/main.c
 create mode 100644 tools/nfsrahead/nfsrahead.man

-- 
2.35.1