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

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Message-ID: <20141220194457.GA3166@x61.redhat.com>
Date:	Sat, 20 Dec 2014 17:44:58 -0200
From:	Rafael Aquini <aquini@...hat.com>
To:	Johannes Weiner <hannes@...xchg.org>
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 01:36:13PM -0500, Johannes Weiner wrote:
> 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.

I'm fine either way, it makes the change even simpler. Also, if we
decide to get rid of page_size != PAGE_SIZE condition I believe we can 
also get rid of that "huge" hint being conditionally printed out too.

-- Rafael
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