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

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Date:	Wed, 14 Jan 2015 12:45:38 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Dave Hansen <dave.hansen@...ux.intel.com>
Cc:	"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 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 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).
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