linux-kernel - Re: [PATCH 8/8] Add VM counters for transparent hugepages

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Message-ID: <20110224231449.GE23252@random.random>
Date:	Fri, 25 Feb 2011 00:14:49 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	Andi Kleen <andi@...stfloor.org>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 8/8] Add VM counters for transparent hugepages

On Thu, Feb 24, 2011 at 02:43:04PM -0800, Dave Hansen wrote:
> On Tue, 2011-02-22 at 17:52 -0800, Andi Kleen wrote:
> > @@ -2286,6 +2290,9 @@ void __split_huge_page_pmd(struct mm_struct *mm, pmd_t *pmd)
> >  		spin_unlock(&mm->page_table_lock);
> >  		return;
> >  	}
> > +
> > +	count_vm_event(THP_SPLIT);
> > +
> >  	page = pmd_page(*pmd);
> >  	VM_BUG_ON(!page_count(page));
> >  	get_page(page);
> 
> Hey Andi,
> 
> Your split counter tracks the split_huge_page_pmd() calls, but misses
> plain split_huge_page() calls.  Did you do this on purpose?  Could we
> move the counter in to the low-level split function like below?

Agreed, I already noticed and posted this same change in Message-ID:
20110224041851.GF31195

> diff -puN mm/huge_memory.c~move-THP_SPLIT mm/huge_memory.c
> --- linux-2.6.git/mm/huge_memory.c~move-THP_SPLIT	2011-02-24 14:37:32.825288409 -0800
> +++ linux-2.6.git-dave/mm/huge_memory.c	2011-02-24 14:39:01.767939971 -0800
> @@ -1342,6 +1342,8 @@ static void __split_huge_page(struct pag
>  	BUG_ON(!PageHead(page));
>  	BUG_ON(PageTail(page));
>  
> +	count_vm_event(THP_SPLIT);
> +
>  	mapcount = 0;
>  	list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
>  		struct vm_area_struct *vma = avc->vma;

I've a micropreference in having it in split_huge_page succeeding path
after __split_huge_page returns, as the __ function is where the
brainer code is and statcode to me is annoying to read mixed in the
more complex code. Not that it makes any practical difference though.
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