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authorZachary Amsden <zach@vmware.com>2005-09-03 15:55:04 -0700
committerLinus Torvalds <torvalds@evo.osdl.org>2005-09-05 00:05:48 -0700
commita600388d28419305aad3c4c0af52c223cf6fa0af (patch)
treec70d3d80275f189c49311183472367f45d1a1ef2 /mm
parentfa5b08d5f818063d18433194f20359ef2ae50254 (diff)
downloadlinux-sh-a600388d28419305aad3c4c0af52c223cf6fa0af.tar.gz
[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>
Diffstat (limited to 'mm')
-rw-r--r--mm/memory.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/mm/memory.c b/mm/memory.c
index b25f5e58a14c..788a62810340 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -562,7 +562,8 @@ static void zap_pte_range(struct mmu_gather *tlb, pmd_t *pmd,
page->index > details->last_index))
continue;
}
- ptent = ptep_get_and_clear(tlb->mm, addr, pte);
+ ptent = ptep_get_and_clear_full(tlb->mm, addr, pte,
+ tlb->fullmm);
tlb_remove_tlb_entry(tlb, pte, addr);
if (unlikely(!page))
continue;
@@ -590,7 +591,7 @@ static void zap_pte_range(struct mmu_gather *tlb, pmd_t *pmd,
continue;
if (!pte_file(ptent))
free_swap_and_cache(pte_to_swp_entry(ptent));
- pte_clear(tlb->mm, addr, pte);
+ pte_clear_full(tlb->mm, addr, pte, tlb->fullmm);
} while (pte++, addr += PAGE_SIZE, addr != end);
pte_unmap(pte - 1);
}