linux-kernel - Re: [PATCH] proc: task_mmu: show page size in /proc/<pid>/numa

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Date:	Sat, 20 Dec 2014 13:36:13 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Rafael Aquini <aquini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	oleg@...hat.com, dave.hansen@...ux.intel.com, rientjes@...gle.com,
	linux-mm@...ck.org
Subject: Re: [PATCH] proc: task_mmu: show page size in /proc/<pid>/numa_maps

On Sat, Dec 20, 2014 at 08:54:45AM -0500, Rafael Aquini wrote:
> This patch introduces 'pagesize' line element to /proc/<pid>/numa_maps
> report file in order to help disambiguating the size of pages that are
> backing memory areas mapped by a task. When the VMA backing page size
> is observed different from kernel's default PAGE_SIZE, the new element 
> is printed out to complement report output. This is specially useful to
> help differentiating between HUGE and GIGANTIC page VMAs.
> 
> This patch is based on Dave Hansen's proposal and reviewer's follow ups 
> taken from this dicussion: https://lkml.org/lkml/2011/9/21/454
> 
> Signed-off-by: Rafael Aquini <aquini@...hat.com>
> ---
>  fs/proc/task_mmu.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 246eae8..9f2e2c8 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1479,6 +1479,7 @@ static int show_numa_map(struct seq_file *m, void *v, int is_pid)
>  	struct mm_struct *mm = vma->vm_mm;
>  	struct mm_walk walk = {};
>  	struct mempolicy *pol;
> +	unsigned long page_size;
>  	char buffer[64];
>  	int nid;
>  
> @@ -1533,6 +1534,10 @@ static int show_numa_map(struct seq_file *m, void *v, int is_pid)
>  	if (!md->pages)
>  		goto out;
>  
> +	page_size = vma_kernel_pagesize(vma);
> +	if (page_size != PAGE_SIZE)
> +		seq_printf(m, " pagesize=%lu", page_size);

It would be simpler to include this unconditionally.  Otherwise you
are forcing everybody parsing the file and trying to run calculations
of it to check for its presence, and then have them fall back and get
the value from somewhere else if not.
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