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Olivier Certner 7a9ea03e4b
vfs: vn_alloc(): Stop always calling vn_alloc_hard() and direct reclaiming 
Commit ab05a1cf32 intended to revert commit 8733bc277a
("vfs: don't provoke recycling non-free vnodes without a good reason"),
but due to intervening changes in commit 054f45e026 ("vfs: further
speed up continuous free vnode recycle"), it also had to revert part of
it.  In particular, while removing the whole 'if (vn_alloc_cyclecount !=
0)' block, it inadvertantly removed the code block resetting
'vn_alloc_cyclecount' to 0 and skipping direct vnode reclamation (done
further below through vnlru_free_locked_direct()), which had been
outside the 'if' before the intervening commit.

Removing this block instead of reinstating it in practice causes
'vn_alloc_cyclecount' to (almost) never be 0, making vn_alloc() always
call vn_alloc_hard(), which takes the 'vnode_list_mtx' mutex.  In other
words, this disables the fast path.  [The reverted commit, which
introduced the 'if (vn_alloc_cyclecount != 0)' guarding this block,
actually never executed it because it also had the bug that
'vn_alloc_cyclecount' would always stay at 0, hiding its usefulness.]

Additionally, not skipping direct vnode reclamation even when there are
less vnodes than 'kern.maxvnodes' not only causes unnecessary contention
but also plain livelocks as vnlru_free_locked_direct() does not itself
check whether there are actually "free" (not referenced) vnodes to be
deallocated, and will blindly browse all the vnode list until it finds
one (which it may not, or only a few ones at the end).  As the fast path
was disabled, all threads in the system would soon be competing for the
vnode list lock, outpacing the vnlru process that could never actually
recycle vnodes in a more agressive manner (i.e., even if they have
a non-zero hold count).  And we could more easily get into this
situation, as each vnode allocation was reducing the count of "free"
vnodes, even if entirely new vnodes could be allocated instead.  This
part was mitigated by the vnlru process (before the tipping point
described above), which explains why the mechanism would not always
livelock.

Not skipping direct vnode reclamation was arguably a bug introduced by
the intervening commit (054f45e026), but was mitigated by
vn_alloc_hard() not being called in the fast path.  The revert commit,
by disabling the fast path, made it significantly annoying (to the point
of getting a few livelocks a week in some of my workloads).

Restore the reset of 'vn_alloc_cyclecount' to 0 and skip direct
reclamation when the current number of vnodes is below the
'kern.maxvnodes' limit, indicating we can start allocating a new 'struct
vnode' right away.  While here, fix the comparison with the limit when
'bumped' is true.

Reviewed by:    kib (older version), avg
Tested by:      avg, olce
Fixes:          ab05a1cf32 (revert of "vfs: don't provoke recycling non-free vnodes without a good reason")
Fixes:          054f45e026 ("vfs: further speed up continuous free vnode recycle")
MFC after:      5 days
Sponsored by:   The FreeBSD Foundation
Differential Revision:  https://reviews.freebsd.org/D50338

(cherry picked from commit d90c9c24e2)
(cherry picked from commit ce6b7a5919da518715d6163baa42035d6d2c1bd0)

Approved by:    re (cperciva)
2025-05-21 12:07:15 +02:00
.cirrus-ci Cirrus-CI: add some timing info on pkg install failure 2021-08-04 15:02:00 -04:00
.github CODEOWNERS: Add nuageinit 2024-09-03 09:05:24 +02:00
bin ps.1: Remove ambiguity in description of option '-J' 2025-05-13 14:41:32 +02:00
cddl libdtrace: Fix an off-by-one in CPU ID handling 2025-04-02 15:14:37 +00:00
contrib MFV: xz 5.8.1. 2025-05-08 09:24:51 -07:00
crypto OpenSSH: Fix logic error in DisableForwarding option 2025-04-14 15:24:47 -04:00
etc tee: add some basic tests 2025-04-25 22:19:48 -05:00
gnu Remove $FreeBSD$: one-line sh pattern 2023-08-16 11:55:03 -06:00
include Add POSIX psiginfo(3) call 2025-04-24 03:27:57 +03:00
kerberos5 kerberos5: Mitigate the possibility of using an old libcrypto 2024-01-22 07:49:05 -08:00
lib MFV: xz 5.8.1. 2025-05-08 09:24:51 -07:00
libexec rc/tests: Fix process flags checks using ps(1) 2025-05-13 14:41:32 +02:00
release EC2: Remove old broken_txfifo workaround 2025-05-15 15:22:44 -07:00
rescue zfs: merge openzfs/zfs@32949f256 (zfs-2.2-release) into stable/14 2023-09-03 09:15:24 +02:00
sbin mount.8: Add a single example for single user mode 2025-04-28 02:01:12 -04:00
secure openssh: Request the OpenSSL 1.1 API 2025-04-03 04:33:21 +00:00
share iwlwifi.4: Update modes for recent 802.11ac 2025-05-19 19:28:40 +00:00
stand loader: provide error message in command_errmsg instead of printing 2025-04-27 21:43:31 -06:00
sys vfs: vn_alloc(): Stop always calling vn_alloc_hard() and direct reclaiming 2025-05-21 12:07:15 +02:00
targets rtlbtfw: Firmware loader for Realtek 87XX/88XX bluetooth USB adaptors 2024-12-22 06:34:35 +03:00
tests queue(3): Add simple tests for some macros for all list/tailq types 2025-05-01 21:48:48 +02:00
tools stress2: exlock2.sh: Fix impact of previous '-U' removal 2025-05-13 14:41:33 +02:00
usr.bin MFV: xz 5.8.1. 2025-05-08 09:24:51 -07:00
usr.sbin bsdinstall: Use a login shell for final configuration. 2025-05-14 20:08:15 +02:00
.arcconfig arcanist: use FreeBSD/git project repository instead of FreeBSD/svn 2022-08-23 14:16:41 +00:00
.arclint arc lint: ignore /tests/ in chmod 2017-12-19 03:38:06 +00:00
.cirrus.yml .cirrus-ci: Update the non-manual GCC build job to GCC 14 2025-04-29 16:43:03 -04:00
.clang-format clang-format: Minor tweaks 2024-05-20 09:42:32 -04:00
.git-blame-ignore-revs .git-blame-ignore-revs: queue(3): Single space after all #define 2025-05-01 21:48:36 +02:00
.gitattributes Add a basic clang-format configuration file 2019-06-07 15:23:52 +00:00
.gitignore .gitignore: Ignore LSP generated .cache 2023-03-07 10:04:18 -05:00
CONTRIBUTING.md CONTRIBUTING.md: fix typo from commmit to commit 2024-03-22 09:30:30 -04:00
COPYRIGHT Happy New Year 2023! 2023-01-01 13:44:43 +08:00
LOCKS Remove $FreeBSD$: one-line bare tag 2023-08-16 11:55:20 -06:00
MAINTAINERS Remove $FreeBSD$: one-line bare tag 2023-08-16 11:55:20 -06:00
Makefile universe: Update the default GCC toolchain to GCC 14 2025-04-29 16:43:10 -04:00
Makefile.inc1 Fix build with WITH_CLANG_BOOTSTRAP and WITHOUT_CLANG 2025-04-23 21:36:00 +02:00
Makefile.libcompat build{libcompat}: Pass UNIVERSE_TOOLCHAIN_PATH to the _lc_build-tools submake 2023-08-21 21:00:45 -07:00
Makefile.sys.inc Remove $FreeBSD$: one-line sh pattern 2023-08-16 11:55:03 -06:00
ObsoleteFiles.inc ObsoleteFiles: Remove mount_fusefs.8 entry 2025-04-21 23:17:52 -04:00
README.md README.md: link to the list of supported platforms 2022-11-01 12:20:55 -03:00
RELNOTES RELNOTES: ps(1): Document change in behavior for '-a'/'-A' 2025-05-13 14:41:26 +02:00
UPDATING ng_ubt: add UPDATING note about firmware downloading on Realtek adaptors 2025-04-30 10:32:23 +03:00

README.md

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