git: kernel - Refactor cache_vref() using counter trick
dillon at crater.dragonflybsd.org
Tue Mar 3 19:39:36 PST 2020
Author: Matthew Dillon <dillon at apollo.backplane.com>
Date: Tue Mar 3 19:35:59 2020 -0800
kernel - Refactor cache_vref() using counter trick
* Refactor cache_vref() such that it is able to validate that a vnode
(whos ref count might be 0) is not in VRECLAIM, without acquiring the
vnode lock. This is the normal case.
If cache_vref() is unable to do this, it backs down to the old method
which was to get a vnode lock, validate that the vnode is not in
VRECLAIM, then release the lock.
* NOTE: In DragonFlyBSD, holding a vref on a vnode (vref, NOT vhold) will
prevent the vnode from transitioning to VRECLAIM.
* Use the new feature for nlookup's naccess() tests and for the *stat*()
series of system calls.
This significantly increases performance. However, we are not entirely
cache-contention free as both the namecache entry and the vnode are still
referenced, requiring atomic adds.
Summary of changes:
sys/kern/vfs_cache.c | 38 ++++++++++++++++++++++++++++++++++++--
sys/kern/vfs_lock.c | 7 +++++++
sys/kern/vfs_nlookup.c | 4 ++--
sys/kern/vfs_syscalls.c | 15 ++++++++++++++-
sys/sys/vnode.h | 1 +
5 files changed, 60 insertions(+), 5 deletions(-)
DragonFly BSD source repository
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