Date: Wed, 17 Aug 2022 10:36:32 GMT From: Mateusz Guzik <mjg@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: f6ffed44a8eb - main - vm: use atomic fetchadd in vm_page_sunbusy Message-ID: <202208171036.27HAaW0P001892@gitrepo.freebsd.org>
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The branch main has been updated by mjg: URL: https://cgit.FreeBSD.org/src/commit/?id=f6ffed44a8eb5d1ab89a18e60fb056aab2105be7 commit f6ffed44a8eb5d1ab89a18e60fb056aab2105be7 Author: Mateusz Guzik <mjg@FreeBSD.org> AuthorDate: 2022-08-05 14:27:55 +0000 Commit: Mateusz Guzik <mjg@FreeBSD.org> CommitDate: 2022-08-17 10:36:11 +0000 vm: use atomic fetchadd in vm_page_sunbusy This also fixes a bug where not-last unbusy failed to post a release fence. Reviewed by: markj (previous version), kib (previous version) Differential Revision: https://reviews.freebsd.org/D36084 --- sys/vm/vm_page.c | 26 ++++++-------------------- 1 file changed, 6 insertions(+), 20 deletions(-) diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c index e7500e9d3e71..defcebb286ae 100644 --- a/sys/vm/vm_page.c +++ b/sys/vm/vm_page.c @@ -973,27 +973,13 @@ vm_page_sunbusy(vm_page_t m) { u_int x; - vm_page_assert_sbusied(m); - - x = vm_page_busy_fetch(m); - for (;;) { - KASSERT(x != VPB_FREED, - ("vm_page_sunbusy: Unlocking freed page.")); - if (VPB_SHARERS(x) > 1) { - if (atomic_fcmpset_int(&m->busy_lock, &x, - x - VPB_ONE_SHARER)) - break; - continue; - } - KASSERT((x & ~VPB_BIT_WAITERS) == VPB_SHARERS_WORD(1), - ("vm_page_sunbusy: invalid lock state")); - if (!atomic_fcmpset_rel_int(&m->busy_lock, &x, VPB_UNBUSIED)) - continue; - if ((x & VPB_BIT_WAITERS) == 0) - break; + atomic_thread_fence_rel(); + x = atomic_fetchadd_int(&m->busy_lock, -VPB_ONE_SHARER); + KASSERT(x != VPB_FREED, ("page %p is freed", m)); + KASSERT(x != VPB_UNBUSIED && (x & VPB_BIT_SHARED) != 0, + ("page %p not sbusied", m)); + if (x == (VPB_SHARERS_WORD(1) | VPB_BIT_WAITERS)) wakeup(m); - break; - } } /*
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