From: Johannes Weiner <hannes@cmpxchg.org>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [rfc 5/5] mincore: transparent huge page support
Date: Thu, 25 Mar 2010 02:23:16 +0100 [thread overview]
Message-ID: <20100325012316.GB27304@cmpxchg.org> (raw)
In-Reply-To: <20100324224858.GP10659@random.random>
On Wed, Mar 24, 2010 at 11:48:58PM +0100, Andrea Arcangeli wrote:
> On Tue, Mar 23, 2010 at 03:35:02PM +0100, Johannes Weiner wrote:
> > +static int mincore_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
> > + unsigned long addr, unsigned long end,
> > + unsigned char *vec)
> > +{
> > + int huge = 0;
> > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > + spin_lock(&vma->vm_mm->page_table_lock);
> > + if (likely(pmd_trans_huge(*pmd))) {
> > + huge = !pmd_trans_splitting(*pmd);
>
> Under mmap_sem (read or write) a hugepage can't materialize under
> us. So here the pmd_trans_huge can be lockless and run _before_ taking
> the page_table_lock. That's the invariant I used to keep identical
> performance for all fast paths.
Wait, there _is_ an unlocked fast-path pmd_trans_huge()
in mincore_pmd_range(), maybe you missed it?
This function is never called if the pmd is not huge.
So the above is the _second check_ under lock to get a stable
read on the entry that could be splitting or already have been
split while we checked locklessly.
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next prev parent reply other threads:[~2010-03-25 1:23 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-23 14:34 mincore and transparent huge pages Johannes Weiner
2010-03-23 14:34 ` [patch 1/5] mincore: cleanups Johannes Weiner
2010-03-23 14:34 ` [patch 2/5] mincore: break do_mincore() into logical pieces Johannes Weiner
2010-03-23 14:35 ` [patch 3/5] mincore: pass ranges as start,end address pairs Johannes Weiner
2010-03-23 14:35 ` [patch 4/5] mincore: do nested page table walks Johannes Weiner
2010-03-23 14:35 ` [rfc 5/5] mincore: transparent huge page support Johannes Weiner
2010-03-24 22:48 ` Andrea Arcangeli
2010-03-25 0:07 ` Johannes Weiner
2010-03-25 0:42 ` Andrea Arcangeli
2010-03-25 1:23 ` Johannes Weiner [this message]
2010-03-24 22:32 ` mincore and transparent huge pages Andrea Arcangeli
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