Date: Sat, 23 Jul 2016 21:56:52 +0000 (UTC) From: Alan Cox <alc@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-11@freebsd.org Subject: svn commit: r303251 - stable/11/sys/vm Message-ID: <201607232156.u6NLuq6I039346@repo.freebsd.org>
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Author: alc Date: Sat Jul 23 21:56:52 2016 New Revision: 303251 URL: https://svnweb.freebsd.org/changeset/base/303251 Log: MFC r303101 Add a comment describing the 'fast path' that was introduced in r270011. Approved by: re (gjb) Modified: stable/11/sys/vm/vm_fault.c Directory Properties: stable/11/ (props changed) Modified: stable/11/sys/vm/vm_fault.c ============================================================================== --- stable/11/sys/vm/vm_fault.c Sat Jul 23 21:22:26 2016 (r303250) +++ stable/11/sys/vm/vm_fault.c Sat Jul 23 21:56:52 2016 (r303251) @@ -354,6 +354,15 @@ RetryFault:; KASSERT((fault_flags & VM_FAULT_WIRE) == 0, ("!wired && VM_FAULT_WIRE")); + /* + * Try to avoid lock contention on the top-level object through + * special-case handling of some types of page faults, specifically, + * those that are both (1) mapping an existing page from the top- + * level object and (2) not having to mark that object as containing + * dirty pages. Under these conditions, a read lock on the top-level + * object suffices, allowing multiple page faults of a similar type to + * run in parallel on the same top-level object. + */ if (fs.vp == NULL /* avoid locked vnode leak */ && (fault_flags & (VM_FAULT_WIRE | VM_FAULT_DIRTY)) == 0 && /* avoid calling vm_object_set_writeable_dirty() */
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