Groups > linux.kernel > #1190348

Re: [PATCH] mm: Flush the TLB for a single address in a huge page

From	Dave Hansen <dave.hansen@intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] mm: Flush the TLB for a single address in a huge page
Date	2015-07-23 01:10 +0200
Message-ID	<pPbjb-5sv-5@gated-at.bofh.it> (permalink)
References	<pP60d-6bF-57@gated-at.bofh.it> <pP9U7-3iz-31@gated-at.bofh.it> <pPaZP-4QP-5@gated-at.bofh.it>
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On 07/22/2015 03:48 PM, Catalin Marinas wrote:
> You are right, on x86 the tlb_single_page_flush_ceiling seems to be
> 33, so for an HPAGE_SIZE range the code does a local_flush_tlb()
> always. I would say a single page TLB flush is more efficient than a
> whole TLB flush but I'm not familiar enough with x86.

The last time I looked, the instruction to invalidate a single page is
more expensive than the instruction to flush the entire TLB.  We also
don't bother doing ranged flushes _ever_ for hugetlbfs TLB
invalidations, but that was just because the work done around commit
e7b52ffd4 didn't see any benefit.

That said, I can't imagine this will hurt anything.  We also have TLBs
that can mix 2M and 4k pages and I don't think we did back when we put
that code in originally.

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Thread

[PATCH] mm: Flush the TLB for a single address in a huge page Catalin Marinas <catalin.marinas@arm.com> - 2015-07-22 19:30 +0200
  Re: [PATCH] mm: Flush the TLB for a single address in a huge page Catalin Marinas <catalin.marinas@arm.com> - 2015-07-23 00:50 +0200
    Re: [PATCH] mm: Flush the TLB for a single address in a huge page Dave Hansen <dave.hansen@intel.com> - 2015-07-23 01:10 +0200
      Re: [PATCH] mm: Flush the TLB for a single address in a huge page Andrea Arcangeli <aarcange@redhat.com> - 2015-07-23 16:20 +0200
        Re: [PATCH] mm: Flush the TLB for a single address in a huge page Andrea Arcangeli <aarcange@redhat.com> - 2015-07-23 19:20 +0200

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