Perforce change 315120

Perforce change 315120

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Change 315120 by devtools@devtools_gitimport on 2011/11/10 18:21:26

	commit a600388d28419305aad3c4c0af52c223cf6fa0af
	Author: Zachary Amsden <zach@vmware.com>
	Date:   Sat Sep 3 15:55:04 2005 -0700
	
	    [PATCH] x86: ptep_clear optimization
	
	    Add a new accessor for PTEs, which passes the full hint from the mmu_gather
	    struct; this allows architectures with hardware pagetables to optimize away
	    atomic PTE operations when destroying an address space.  Removing the
	    locked operation should allow better pipelining of memory access in this
	    loop.  I measured an average savings of 30-35 cycles per zap_pte_range on
	    the first 500 destructions on Pentium-M, but I believe the optimization
	    would win more on older processors which still assert the bus lock on xchg
	    for an exclusive cacheline.
	
	    Update: I made some new measurements, and this saves exactly 26 cycles over
	    ptep_get_and_clear on Pentium M.  On P4, with a PAE kernel, this saves 180
	    cycles per ptep_get_and_clear, for a whopping 92160 cycles savings for a
	    full address space destruction.
	
	    pte_clear_full is not yet used, but is provided for future optimizations
	    (in particular, when running inside of a hypervisor that queues page table
	    updates, the full hint allows us to avoid queueing unnecessary page table
	    update for an address space in the process of being destroyed.
	
	    This is not a huge win, but it does help a bit, and sets the stage for
	    further hypervisor optimization of the mm layer on all architectures.
	
	    Signed-off-by: Zachary Amsden <zach@vmware.com>
	    Cc: Christoph Lameter <christoph@lameter.com>
	    Cc: <linux-mm@kvack.org>
	    Signed-off-by: Andrew Morton <akpm@osdl.org>
	    Signed-off-by: Linus Torvalds <torvalds@osdl.org>

Affected files ...

... //sw/components_third_party/linux/git/master/.versions.submit#1698 edit
... //sw/components_third_party/linux/git/master/component/include/asm-generic/pgtable.h#4 edit
... //sw/components_third_party/linux/git/master/component/include/asm-i386/pgtable.h#7 edit
... //sw/components_third_party/linux/git/master/component/mm/memory.c#13 edit

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