From: Will Deacon <will.deacon@arm.com>
To: Ralf Baechle <ralf@linux-mips.org>
Cc: Catalin Marinas <Catalin.Marinas@arm.com>,
Andrew Morton <akpm@linux-foundation.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"mhocko@suse.cz" <mhocko@suse.cz>,
Steve Capper <Steve.Capper@arm.com>
Subject: Re: [PATCH 2/3] mm: thp: Fix the update_mmu_cache() last argument passing in mm/huge_memory.c
Date: Thu, 20 Sep 2012 13:44:01 +0100 [thread overview]
Message-ID: <20120920124401.GF4654@mudshark.cambridge.arm.com> (raw)
In-Reply-To: <20120919155346.GB32398@linux-mips.org>
Hi Ralf,
On Wed, Sep 19, 2012 at 04:53:46PM +0100, Ralf Baechle wrote:
> On Wed, Sep 19, 2012 at 10:12:28AM +0100, Catalin Marinas wrote:
>
> > >> 5) void update_mmu_cache(struct vm_area_struct *vma,
> > >> unsigned long address, pte_t *ptep)
> > >
> > > Yes please.
> >
> > Should we just use a generic (void *) for the last argument or force a
> > cast in mm/huge_memory.c?
> >
> > Ralf's point is that transparent huge page code calls update_mmu_cache
> > with a (pmd_t *) as the last argument. This could make sense for THP
> > as it assumes that huge pages can only be created at the pmd level.
> > But that's unlike mm/hugetlb.c which casts huge page types to pte_t,
> > even though on ARM they are implemented at the pmd level.
> >
> > On ARM (with VIPT caches) update_mmu_cache() is empty like on x86,
> > though a static inline rather than macro.
>
> It's even worse - mm/huge_memory.c is passing a pmd_t, not a pointer so
> changing the type of update_mmu_cache's 3rd argument alone won't cut it.
>
> This went unnoticed so far because all existing architectures supporting
> transparent huge pages implement update_mmu_cache() as do { } while (0).
>
> MIPS uses update_mmu_cache() as the hook to deal with cache aliases and
> pre-faulting a TLB entry. But aliases don't affect small pages and having
> a separate variant of update_mmu_cache for huge pages will allow some other
> optimizations. That's minor but it's the argument types that really need
> to be fixed and because MIPS also implements huge pages at PMD level I'd
> be happy if we settle on pte_t * for mm/huge_memory.c.
Just to clarify: do you want a cast from pmd_t * to pte_t * or instead copy
the hugetlb code and pass ptes around instead of pmds? The latter is pretty
invasive...
Will
next prev parent reply other threads:[~2012-09-20 12:44 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-11 16:47 [PATCH 0/3] Minor changes to common hugetlb code for ARM Will Deacon
2012-09-11 16:47 ` [PATCH 1/3] mm: thp: Fix the pmd_clear() arguments in pmdp_get_and_clear() Will Deacon
2012-09-11 17:12 ` Kirill A. Shutemov
2012-09-12 15:30 ` Michal Hocko
2012-09-11 16:47 ` [PATCH 2/3] mm: thp: Fix the update_mmu_cache() last argument passing in mm/huge_memory.c Will Deacon
2012-09-11 17:38 ` Kirill A. Shutemov
2012-09-12 15:40 ` Michal Hocko
2012-09-12 15:51 ` Catalin Marinas
2012-09-15 13:38 ` Ralf Baechle
2012-09-18 19:33 ` Andrew Morton
2012-09-19 9:12 ` Catalin Marinas
2012-09-19 15:53 ` Ralf Baechle
2012-09-20 12:44 ` Will Deacon [this message]
2012-09-20 19:32 ` David Miller
2012-09-11 16:47 ` [PATCH 3/3] mm: Introduce HAVE_ARCH_TRANSPARENT_HUGEPAGE Will Deacon
2012-09-11 17:41 ` Kirill A. Shutemov
2012-09-12 15:32 ` Michal Hocko
2012-09-12 18:06 ` Chris Metcalf
2012-09-12 18:10 ` Will Deacon
2012-09-13 19:05 ` Andrew Morton
2012-09-13 21:26 ` Will Deacon
2012-09-13 21:27 ` Stephen Rothwell
2012-09-13 21:40 ` Andrew Morton
2012-09-12 15:27 ` [PATCH 0/3] Minor changes to common hugetlb code for ARM Michal Hocko
2012-09-12 15:55 ` Will Deacon
2012-09-13 12:22 ` Michal Hocko
2012-09-13 0:12 ` Andrea Arcangeli
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