linux-kernel - Re: [PATCH 2/6] thp: optimize away unnecessary page table locking

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Message-ID: <CAJd=RBB2GMRQNUH+2z7R5Fy6OKKtid9wn2mTFORvtefo+wUaOQ@mail.gmail.com>
Date:	Sat, 14 Jan 2012 11:24:06 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Andi Kleen <andi@...stfloor.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/6] thp: optimize away unnecessary page table locking

On Fri, Jan 13, 2012 at 11:14 PM, Naoya Horiguchi
<n-horiguchi@...jp.nec.com> wrote:
> Hi Hillf,
>
> (1/13/2012 7:04), Hillf Danton wrote:
> [...]
>>> +/*
>>> + * Returns 1 if a given pmd is mapping a thp and stable (not under splitting.)
>>> + * Returns 0 otherwise. Note that if it returns 1, this routine returns without
>>> + * unlocking page table locks. So callers must unlock them.
>>> + */
>>> +int pmd_trans_huge_stable(pmd_t *pmd, struct vm_area_struct *vma)
>>> +{
>>> +       VM_BUG_ON(!rwsem_is_locked(&vma->vm_mm->mmap_sem));
>>> +
>>> +       if (!pmd_trans_huge(*pmd))
>>> +               return 0;
>>> +
>>> +       spin_lock(&vma->vm_mm->page_table_lock);
>>> +       if (likely(pmd_trans_huge(*pmd))) {
>>> +               if (pmd_trans_splitting(*pmd)) {
>>> +                       spin_unlock(&vma->vm_mm->page_table_lock);
>>> +                       wait_split_huge_page(vma->anon_vma, pmd);
>>> +                       return 0;
>>> +               } else {
>>
>>                             spin_unlock(&vma->vm_mm->page_table_lock);     yes?
>
> No. Unlocking is supposed to be done by the caller as commented.
>
Thanks for correcting /Hillf
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