From: Andrea Arcangeli <aarcange@redhat.com>
To: Dave Hansen <dave@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Michael J Wolf <mjwolf@us.ibm.com>,
Johannes Weiner <hannes@cmpxchg.org>,
David Rientjes <rientjes@google.com>
Subject: Re: [PATCH 4/5] teach smaps_pte_range() about THP pmds
Date: Thu, 10 Feb 2011 19:08:02 +0100 [thread overview]
Message-ID: <20110210180801.GA3347@random.random> (raw)
In-Reply-To: <20110209195411.816D55A7@kernel>
On Wed, Feb 09, 2011 at 11:54:11AM -0800, Dave Hansen wrote:
> @@ -385,8 +387,16 @@ static int smaps_pte_range(pmd_t *pmd, u
> pte_t *pte;
> spinlock_t *ptl;
>
> - split_huge_page_pmd(walk->mm, pmd);
> -
> + if (pmd_trans_huge(*pmd)) {
> + if (pmd_trans_splitting(*pmd)) {
> + spin_unlock(&walk->mm->page_table_lock);
> + wait_split_huge_page(vma->anon_vma, pmd);
> + spin_lock(&walk->mm->page_table_lock);
the locking looks wrong, who is taking the &walk->mm->page_table_lock,
and isn't this going to deadlock on the pte_offset_map_lock for
NR_CPUS < 4, and where is it released? This spin_lock don't seem
necessary to me.
The right locking would be:
spin_lock(&walk->mm->page_table_lock);
if (pmd_trans_huge(*pmd)) {
if (pmd_trans_splitting(*pmd)) {
spin_unlock(&walk->mm->page_table_lock);
wait_split_huge_page(vma->anon_vma, pmd);
} else {
smaps_pte_entry(*(pte_t *)pmd, addr, HPAGE_SIZE, walk);
spin_unlock(&walk->mm->page_table_lock);
return 0;
}
I think it worked because you never run into a pmd_trans_splitting pmd
yet, and you were running smaps_pte_entry lockless which could race
against split_huge_page (but it normally doesn't).
> + } else {
> + smaps_pte_entry(*(pte_t *)pmd, addr, HPAGE_SIZE, walk);
> + return 0;
> + }
> + }
> pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> for (; addr != end; pte++, addr += PAGE_SIZE)
> smaps_pte_entry(*pte, addr, PAGE_SIZE, walk);
> _
>
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next prev parent reply other threads:[~2011-02-10 18:08 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-02-09 19:54 [PATCH 0/5] fix up /proc/$pid/smaps to not split huge pages Dave Hansen
2011-02-09 19:54 ` [PATCH 1/5] pagewalk: only split huge pages when necessary Dave Hansen
2011-02-10 11:11 ` Mel Gorman
2011-02-10 13:19 ` Andrea Arcangeli
2011-02-10 13:34 ` Mel Gorman
2011-02-09 19:54 ` [PATCH 2/5] break out smaps_pte_entry() from smaps_pte_range() Dave Hansen
2011-02-10 11:15 ` Mel Gorman
2011-02-09 19:54 ` [PATCH 3/5] pass pte size argument in to smaps_pte_entry() Dave Hansen
2011-02-10 11:16 ` Mel Gorman
2011-02-09 19:54 ` [PATCH 4/5] teach smaps_pte_range() about THP pmds Dave Hansen
2011-02-10 11:17 ` Mel Gorman
2011-02-10 18:08 ` Andrea Arcangeli [this message]
2011-02-10 19:32 ` Dave Hansen
2011-02-09 19:54 ` [PATCH 5/5] have smaps show transparent huge pages Dave Hansen
2011-02-10 11:20 ` Mel Gorman
2011-02-10 15:01 ` Dave Hansen
2011-02-10 15:09 ` Mel Gorman
2011-02-10 18:09 ` Andrea Arcangeli
2011-02-10 18:20 ` Dave Hansen
2011-02-10 18:39 ` Andrea Arcangeli
2011-02-09 21:24 ` [PATCH 0/5] fix up /proc/$pid/smaps to not split " Andrea Arcangeli
2011-02-20 21:54 ` David Rientjes
2011-02-15 16:55 ` Eric B Munson
2011-02-15 17:01 ` Andrea Arcangeli
2011-02-15 17:05 ` Dave Hansen
2011-02-15 18:00 ` Andrea Arcangeli
-- strict thread matches above, loose matches on Subject: below --
2011-02-22 1:53 Dave Hansen
2011-02-22 1:53 ` [PATCH 4/5] teach smaps_pte_range() about THP pmds Dave Hansen
2011-02-22 13:35 ` Andrea Arcangeli
2011-02-22 21:22 ` David Rientjes
2011-02-23 15:31 ` Eric B Munson
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