linux-kernel - Re: [PATCH 1/2] mm: rename mm->nr_ptes to mm->nr

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Date:	Wed, 14 Jan 2015 16:33:58 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Dave Hansen <dave.hansen@...ux.intel.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
	Pavel Emelyanov <xemul@...nvz.org>,
	linux-kernel@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 1/2] mm: rename mm->nr_ptes to mm->nr_pgtables

On Wed, Jan 14, 2015 at 12:45:38PM +0300, Cyrill Gorcunov wrote:
> On Tue, Jan 13, 2015 at 01:49:10PM -0800, Dave Hansen wrote:
> > On 01/13/2015 01:43 PM, Cyrill Gorcunov wrote:
> > > On Tue, Jan 13, 2015 at 09:14:15PM +0200, Kirill A. Shutemov wrote:
> > >> We're going to account pmd page tables too. Let's rename mm->nr_pgtables
> > >> to something more generic.
> > >>
> > >> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > >> --- a/fs/proc/task_mmu.c
> > >> +++ b/fs/proc/task_mmu.c
> > >> @@ -64,7 +64,7 @@ void task_mem(struct seq_file *m, struct mm_struct *mm)
> > >>  		data << (PAGE_SHIFT-10),
> > >>  		mm->stack_vm << (PAGE_SHIFT-10), text, lib,
> > >>  		(PTRS_PER_PTE * sizeof(pte_t) *
> > >> -		 atomic_long_read(&mm->nr_ptes)) >> 10,
> > >> +		 atomic_long_read(&mm->nr_pgtables)) >> 10,
> > > 
> > > This implies that (PTRS_PER_PTE * sizeof(pte_t)) = (PTRS_PER_PMD * sizeof(pmd_t))
> > > which might be true for all archs, right?

I doubt it. And even if it's true now, nobody can guarantee that this will
be true for all future configurations.

> > I wonder if powerpc is OK on this front today.  This diagram:
> > 
> > 	http://linux-mm.org/PageTableStructure
> > 
> > says that they use a 128-byte "pte" table when mapping 16M pages.  I
> > wonder if they bump mm->nr_ptes for these.
> 
> It looks like this doesn't matter. The statistics here prints the size
> of summary memory occupied for pte_t entries, here PTRS_PER_PTE * sizeof(pte_t)
> is only valid for, once we start accounting pmd into same counter it implies
> that PTRS_PER_PTE == PTRS_PER_PMD, which is not true for all archs
> (if I understand the idea of accounting here right).

Yeah. good catch. Thank you.

I'll respin with separate counter for pmd tables. It seems the best
option.

-- 
 Kirill A. Shutemov
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