Re: [PATCH V3] powerpc/mm: Fix Multi hit ERAT cause by recent THP update

From	Balbir Singh <bsingharora@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH V3] powerpc/mm: Fix Multi hit ERAT cause by recent THP update
Date	2016-02-16 06:30 +0100
Message-ID	<r2Gn0-3iF-1@gated-at.bofh.it> (permalink)
References	<r05hT-58m-1@gated-at.bofh.it> <r2hoC-34W-7@gated-at.bofh.it> <r2j74-4hS-5@gated-at.bofh.it> <r2jJL-4NE-3@gated-at.bofh.it> <r2pct-6M-13@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On Mon, 2016-02-15 at 16:31 +0530, Aneesh Kumar K.V wrote:
> Balbir Singh <bsingharora@gmail.com> writes:
> 
> > > Now we can't depend for mm_cpumask, a parallel find_linux_pte_hugepte
> > > can happen outside that. Now i had a variant for kick_all_cpus_sync that
> > > ignored idle cpus. But then that needs more verification.
> > > 
> > > http://article.gmane.org/gmane.linux.ports.ppc.embedded/81105
> > Can be racy as a CPU moves from non-idle to idle
> > 
> > In
> > 
> > > +     pmd_hugepage_update(vma->vm_mm, address, pmdp, ~0UL, 0);
> > > +     /*
> > > +      * This ensures that generic code that rely on IRQ disabling
> > > +      * to prevent a parallel THP split work as expected.
> > > +      */
> > > +     kick_all_cpus_sync();
> > 
> > pmdp_invalidate()->pmd_hugepage_update() can still run in parallel with 
> > find_linux_pte_or_hugepte() and race.. Am I missing something?
> > 
> 
> Yes. But then we make sure that the pte_t returned by
> find_linux_pte_or_hugepte doesn't change to a regular pmd entry by using
> that kick. Now callers of find_lnux_pte_or_hugepte will check for
> _PAGE_PRESENT. So if it called before
> pmd_hugepage_update(_PAGE_PRESENT), we wait for the caller to finish the
> usage (via kick()). Or they bail out after finding _PAGE_PRESENT cleared.

Makes sense, but I would still check the assumption about checking for
_PAGE_PRESENT

Balbir Singh

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

Re: [PATCH V3] powerpc/mm: Fix Multi hit ERAT cause by recent THP  update Balbir Singh <bsingharora@gmail.com> - 2016-02-15 03:50 +0100
  Re: [PATCH V3] powerpc/mm: Fix Multi hit ERAT cause by recent THP update "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> - 2016-02-15 05:40 +0100
    Re: [PATCH V3] powerpc/mm: Fix Multi hit ERAT cause by recent THP  update Balbir Singh <bsingharora@gmail.com> - 2016-02-15 06:20 +0100
      Re: [PATCH V3] powerpc/mm: Fix Multi hit ERAT cause by recent THP update "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> - 2016-02-15 12:10 +0100
        Re: [PATCH V3] powerpc/mm: Fix Multi hit ERAT cause by recent THP  update Balbir Singh <bsingharora@gmail.com> - 2016-02-16 06:30 +0100

csiph-web