linux-kernel - Re: [PATCH v3 09/13] memcg: apply walk_page

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Message-ID: <20140630143105.GB4319@nhori.bos.redhat.com>
Date:	Mon, 30 Jun 2014 10:31:05 -0400
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave.hansen@...el.com>,
	Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org,
	Naoya Horiguchi <nao.horiguchi@...il.com>
Subject: Re: [PATCH v3 09/13] memcg: apply walk_page_vma()

On Mon, Jun 30, 2014 at 03:20:16PM +0300, Kirill A. Shutemov wrote:
> On Fri, Jun 20, 2014 at 04:11:35PM -0400, Naoya Horiguchi wrote:
> > pagewalk.c can handle vma in itself, so we don't have to pass vma via
> > walk->private. And both of mem_cgroup_count_precharge() and
> > mem_cgroup_move_charge() walk over all vmas (not interested in outside vma,)
> > so using walk_page_vma() is preferable.
> > 
> > Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> 
> My first thought was to suggest walk_page_range(0, -1, &walk) instead
> since we walk over all vmas. But walk_page_range() uses find_vma() on each
> iteration, which is expensive.
> Is there a reason why we cannot use vma->vm_next in walk_page_range()?

Right, we can use vma->vm_next. The old code uses find_vma() because
addr can jump to the next pgd boundary, but that doesn't happen with
this patch, so using vma->vm_next is fine.

Thanks,
Naoya Horiguchi
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