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SubjectRe: [patch 1/5] avoid tlb gather restarts.
On Tue, 3 Jul 2007, Martin Schwidefsky wrote:
> From: Martin Schwidefsky <schwidefsky@de.ibm.com>
>
> If need_resched() is false in the inner loop of unmap_vmas it is
> unnecessary to do a full blown tlb_finish_mmu / tlb_gather_mmu for
> each ZAP_BLOCK_SIZE ptes. Do a tlb_flush_mmu() instead. That gives
> architectures with a non-generic tlb flush implementation room for
> optimization. The tlb_flush_mmu primitive is a available with the
> generic tlb flush code, the ia64_tlb_flush_mm needs to be renamed
> and a dummy function is added to arm and arm26.
>
> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

Acked-by: Hugh Dickins <hugh@veritas.com>

(Looking at it, I see that we could argue that there ought to be a
need_resched() etc. check after your tlb_flush_mmu() in unmap_vmas,
in case it's spent a long while in there on some arches; but I don't
think we have the ZAP_BLOCK_SIZE tuned with any great precision, and
you'd at worst be doubling the latency there, so let's not worry
about it. I write this merely in order to reserve myself an
"I told you so" if anyone ever notices increased latency ;)

> ---
>
> include/asm-arm/tlb.h | 5 +++++
> include/asm-arm26/tlb.h | 5 +++++
> include/asm-ia64/tlb.h | 6 +++---
> mm/memory.c | 16 ++++++----------
> 4 files changed, 19 insertions(+), 13 deletions(-)
>
> diff -urpN linux-2.6/include/asm-arm/tlb.h linux-2.6-patched/include/asm-arm/tlb.h
> --- linux-2.6/include/asm-arm/tlb.h 2006-11-08 10:45:43.000000000 +0100
> +++ linux-2.6-patched/include/asm-arm/tlb.h 2007-07-03 12:56:46.000000000 +0200
> @@ -52,6 +52,11 @@ tlb_gather_mmu(struct mm_struct *mm, uns
> }
>
> static inline void
> +tlb_flush_mmu(struct mmu_gather *tlb, unsigned long start, unsigned long end)
> +{
> +}
> +
> +static inline void
> tlb_finish_mmu(struct mmu_gather *tlb, unsigned long start, unsigned long end)
> {
> if (tlb->fullmm)
> diff -urpN linux-2.6/include/asm-arm26/tlb.h linux-2.6-patched/include/asm-arm26/tlb.h
> --- linux-2.6/include/asm-arm26/tlb.h 2006-11-08 10:45:43.000000000 +0100
> +++ linux-2.6-patched/include/asm-arm26/tlb.h 2007-07-03 12:56:46.000000000 +0200
> @@ -29,6 +29,11 @@ tlb_gather_mmu(struct mm_struct *mm, uns
> }
>
> static inline void
> +tlb_flush_mmu(struct mmu_gather *tlb, unsigned long start, unsigned long end)
> +{
> +}
> +
> +static inline void
> tlb_finish_mmu(struct mmu_gather *tlb, unsigned long start, unsigned long end)
> {
> if (tlb->need_flush)
> diff -urpN linux-2.6/include/asm-ia64/tlb.h linux-2.6-patched/include/asm-ia64/tlb.h
> --- linux-2.6/include/asm-ia64/tlb.h 2006-11-08 10:45:45.000000000 +0100
> +++ linux-2.6-patched/include/asm-ia64/tlb.h 2007-07-03 12:56:46.000000000 +0200
> @@ -72,7 +72,7 @@ DECLARE_PER_CPU(struct mmu_gather, mmu_g
> * freed pages that where gathered up to this point.
> */
> static inline void
> -ia64_tlb_flush_mmu (struct mmu_gather *tlb, unsigned long start, unsigned long end)
> +tlb_flush_mmu (struct mmu_gather *tlb, unsigned long start, unsigned long end)
> {
> unsigned int nr;
>
> @@ -160,7 +160,7 @@ tlb_finish_mmu (struct mmu_gather *tlb,
> * Note: tlb->nr may be 0 at this point, so we can't rely on tlb->start_addr and
> * tlb->end_addr.
> */
> - ia64_tlb_flush_mmu(tlb, start, end);
> + tlb_flush_mmu(tlb, start, end);
>
> /* keep the page table cache within bounds */
> check_pgt_cache();
> @@ -184,7 +184,7 @@ tlb_remove_page (struct mmu_gather *tlb,
> }
> tlb->pages[tlb->nr++] = page;
> if (tlb->nr >= FREE_PTE_NR)
> - ia64_tlb_flush_mmu(tlb, tlb->start_addr, tlb->end_addr);
> + tlb_flush_mmu(tlb, tlb->start_addr, tlb->end_addr);
> }
>
> /*
> diff -urpN linux-2.6/mm/memory.c linux-2.6-patched/mm/memory.c
> --- linux-2.6/mm/memory.c 2007-06-18 09:43:22.000000000 +0200
> +++ linux-2.6-patched/mm/memory.c 2007-07-03 12:56:46.000000000 +0200
> @@ -853,18 +853,15 @@ unsigned long unmap_vmas(struct mmu_gath
> break;
> }
>
> - tlb_finish_mmu(*tlbp, tlb_start, start);
> -
> if (need_resched() ||
> (i_mmap_lock && need_lockbreak(i_mmap_lock))) {
> - if (i_mmap_lock) {
> - *tlbp = NULL;
> + if (i_mmap_lock)
> goto out;
> - }
> + tlb_finish_mmu(*tlbp, tlb_start, start);
> cond_resched();
> - }
> -
> - *tlbp = tlb_gather_mmu(vma->vm_mm, fullmm);
> + *tlbp = tlb_gather_mmu(vma->vm_mm, fullmm);
> + } else
> + tlb_flush_mmu(*tlbp, tlb_start, start);
> tlb_start_valid = 0;
> zap_work = ZAP_BLOCK_SIZE;
> }
> @@ -892,8 +889,7 @@ unsigned long zap_page_range(struct vm_a
> tlb = tlb_gather_mmu(mm, 0);
> update_hiwater_rss(mm);
> end = unmap_vmas(&tlb, vma, address, end, &nr_accounted, details);
> - if (tlb)
> - tlb_finish_mmu(tlb, address, end);
> + tlb_finish_mmu(tlb, address, end);
> return end;
> }
>
-
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