This allows making half-constructed entries visible to the lockless lookup,
which now can check for either "not yet fully constructed" and "no longer valid"
state.
This will be used for .. lookup.
cache_purge locklessly checks whether the vnode at hand has any namecache
entries. This can race with a concurrent purge which managed to remove
the last entry, but may not be done touching the vnode.
Make sure we observe the relevant vnode lock as not taken before proceeding
with vgone.
Paired with the fact that doomed vnodes cannnot receive entries this restores
the invariant that there are no namecache-related writing users past cache_purge
in vgone.
Reported by: pho
This significantly speeds up path lookup, Cascade Lake doing access(2) on ufs
on /usr/obj/usr/src/amd64.amd64/sys/GENERIC/vnode_if.c, ops/s:
before: 2535298
after: 2797621
Over +10%.
The reversed order of computation here does not seem to matter for hash
distribution.
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D25921
This makes the realpath syscall operational with the new lookup. Note that the
walk to obtain the full path name still takes locks.
Tested by: pho
Differential Revision: https://reviews.freebsd.org/D23917
Provides full scalability as long as all visited filesystems support the
lookup and terminal vnodes are different.
Inner workings are explained in the comment above cache_fplookup.
Capabilities and fd-relative lookups are not supported and will result in
immediate fallback to regular code.
Symlinks, ".." in the path, mount points without support for lockless lookup
and mismatched counters will result in an attempt to get a reference to the
directory vnode and continue in regular lookup. If this fails, the entire
operation is aborted and regular lookup starts from scratch. However, care is
taken that data is not copied again from userspace.
Sample benchmark:
incremental -j 104 bzImage on tmpfs:
before: 142.96s user 1025.63s system 4924% cpu 23.731 total
after: 147.36s user 313.40s system 3216% cpu 14.326 total
Sample microbenchmark: access calls to separate files in /tmpfs, 104 workers, ops/s:
before: 2165816
after: 151216530
Reviewed by: kib
Tested by: pho (in a patchset)
Differential Revision: https://reviews.freebsd.org/D25578
Previously it would check 4, 3, 2, 1 lists. In practice by the time
it is getting called all lists have some elements and consequently
this does not result in new evictions.
Nonetheless, the code is clearer.
Tested by: pho
.. and stuff if into the unused target vnode field
This gets rid of concurrent nc_flag modifications racing with the
shrinker and consequently fixes a bug where such a change could have
been missed when cache_ncp_invalidate was being issued..
Reported by: zeising
Tested by: pho, zeising
Fixes: r362828 ("cache: lockless forward lookup with smr")
This eliminates the need to take bucket locks in the common case.
Concurrent lookup utilizng the same vnodes is still bottlenecked on referencing
and locking path components, this will be taken care of separately.
Reviewed by: kib
Tested by: pho
Differential Revision: https://reviews.freebsd.org/D23913
The new structure is copy-on-write. With the assumption that path lookups are
significantly more frequent than chdirs and chrooting this is a win.
This provides stable root and jail root vnodes without the need to reference
them on lookup, which in turn means less work on globally shared structures.
Note this also happens to fix a bug where jail vnode was never referenced,
meaning subsequent access on lookup could run into use-after-free.
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D23884
r357614 added CTLFLAG_NEEDGIANT to make it easier to find nodes that are
still not MPSAFE (or already are but aren’t properly marked).
Use it in preparation for a general review of all nodes.
This is non-functional change that adds annotations to SYSCTL_NODE and
SYSCTL_PROC nodes using one of the soon-to-be-required flags.
Mark all obvious cases as MPSAFE. All entries that haven't been marked
as MPSAFE before are by default marked as NEEDGIANT
Approved by: kib (mentor, blanket)
Commented by: kib, gallatin, melifaro
Differential Revision: https://reviews.freebsd.org/D23718
realpath(3) is used a lot e.g., by clang and is a major source of getcwd
and fstatat calls. This can be done more efficiently in the kernel.
This works by performing a regular lookup while saving the name and found
parent directory. If the terminal vnode is a directory we can resolve it using
usual means. Otherwise we can use the name saved by lookup and resolve the
parent.
See the review for sample syscall counts.
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D23574
O_SEARCH is defined by POSIX [0] to open a directory for searching, skipping
permissions checks on the directory itself after the initial open(). This is
close to the semantics we've historically applied for O_EXEC on a directory,
which is UB according to POSIX. Conveniently, O_SEARCH on a file is also
explicitly undefined behavior according to POSIX, so O_EXEC would be a fine
choice. The spec goes on to state that O_SEARCH and O_EXEC need not be
distinct values, but they're not defined to be the same value.
This was pointed out as an incompatibility with other systems that had made
its way into libarchive, which had assumed that O_EXEC was an alias for
O_SEARCH.
This defines compatibility O_SEARCH/FSEARCH (equivalent to O_EXEC and FEXEC
respectively) and expands our UB for O_EXEC on a directory. O_EXEC on a
directory is checked in vn_open_vnode already, so for completeness we add a
NOEXECCHECK when O_SEARCH has been specified on the top-level fd and do not
re-check that when descending in namei.
[0] https://pubs.opengroup.org/onlinepubs/9699919799/
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D23247
Filesystems which want to use it in limited capacity can employ the
VOP_UNLOCK_FLAGS macro.
Reviewed by: kib (previous version)
Differential Revision: https://reviews.freebsd.org/D21427
The current vnode layout is not smp-friendly by having frequently read data
avoidably sharing cachelines with very frequently modified fields. In
particular v_iflag inspected for VI_DOOMED can be found in the same line with
v_usecount. Instead make it available in the same cacheline as the v_op, v_data
and v_type which all get read all the time.
v_type is avoidably 4 bytes while the necessary data will easily fit in 1.
Shrinking it frees up 3 bytes, 2 of which get used here to introduce a new
flag field with a new value: VIRF_DOOMED.
Reviewed by: kib, jeff
Differential Revision: https://reviews.freebsd.org/D22715
. entries are never created and .. can reuse existing entries,
meaning the early count bump is both spurious and leading to
overcounting in certain cases.
The current mechanism is bogus in several ways:
- the limit is a percentage of total entries added, which means negative
entries get evicted all the time even if there are plenty of resources
- evicting code is almost not concurrent, which makes it unable to
remove entries fast enough when doing something as simple as -j 104
buildworld
- there is no support for performing mass removal if necessary
Vast majority of negative entries never get any hits. Only evicting
them when the filesystem demands it results in a significant growth of
the namecache with almost no improvement in the hit ratio.
Sample result about afer 90 minutes of poudriere -j 104:
current no evict % of the original
numneg 219737 2013157 916
numneghits 266711906 263544562 98 [1]
[1] this may look funny but there is a certain dose of variation to the
build
The number was chosen as something which mostly eliminates spurious
evictions during lighter workloads but still keeps the total at bay.
Sponsored by: The FreeBSD Foundation
Continue protecting demotion from the hotlist and selection of the
target list with the ncneg_shrink_lock lock, but drop it before
relocking to zap the node.
While here count how many times we skipped shrinking due to the lock
being already taken.
Sponsored by: The FreeBSD Foundation
