Date: Wed, 20 Jul 2016 17:20:22 +0000 (UTC) From: Alan Cox <alc@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r303101 - head/sys/vm Message-ID: <201607201720.u6KHKMOZ018495@repo.freebsd.org>
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Author: alc Date: Wed Jul 20 17:20:22 2016 New Revision: 303101 URL: https://svnweb.freebsd.org/changeset/base/303101 Log: Add a comment describing the 'fast path' that was introduced in r270011. Reviewed by: kib MFC after: 3 days Sponsored by: EMC / Isilon Storage Division Modified: head/sys/vm/vm_fault.c Modified: head/sys/vm/vm_fault.c ============================================================================== --- head/sys/vm/vm_fault.c Wed Jul 20 17:19:47 2016 (r303100) +++ head/sys/vm/vm_fault.c Wed Jul 20 17:20:22 2016 (r303101) @@ -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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