linux-kernel - Re: [PATCH] hugetlb: /proc/meminfo shows data for all sizes of hugepages

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Date:	Tue, 8 Mar 2011 08:14:49 +0900
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Petr Holasek <pholasek@...hat.com>,
	linux-kernel@...r.kernel.org, emunson@...bm.net, anton@...hat.com,
	Andi Kleen <ak@...ux.intel.com>, Mel Gorman <mel@....ul.ie>,
	Wu Fengguang <fengguang.wu@...el.com>, linux-mm@...ck.org
Subject: Re: [PATCH] hugetlb: /proc/meminfo shows data for all sizes of
 hugepages

On Mon, Mar 07, 2011 at 02:51:49PM -0800, Andrew Morton wrote:
> On Mon, 07 Mar 2011 11:46:54 -0800
> Dave Hansen <dave@...ux.vnet.ibm.com> wrote:
>
> > On Mon, 2011-03-07 at 14:05 +0100, Petr Holasek wrote:
> > > +       for_each_hstate(h)
> > > +               seq_printf(m,
> > > +                               "HugePages_Total:   %5lu\n"
> > > +                               "HugePages_Free:    %5lu\n"
> > > +                               "HugePages_Rsvd:    %5lu\n"
> > > +                               "HugePages_Surp:    %5lu\n"
> > > +                               "Hugepagesize:   %8lu kB\n",
> > > +                               h->nr_huge_pages,
> > > +                               h->free_huge_pages,
> > > +                               h->resv_huge_pages,
> > > +                               h->surplus_huge_pages,
> > > +                               1UL << (huge_page_order(h) + PAGE_SHIFT - 10));
> > >  }
> >
> > It sounds like now we'll get a meminfo that looks like:
> >
> > ...
> > AnonHugePages:    491520 kB
> > HugePages_Total:       5
> > HugePages_Free:        2
> > HugePages_Rsvd:        3
> > HugePages_Surp:        1
> > Hugepagesize:       2048 kB
> > HugePages_Total:       2
> > HugePages_Free:        1
> > HugePages_Rsvd:        1
> > HugePages_Surp:        1
> > Hugepagesize:    1048576 kB
> > DirectMap4k:       12160 kB
> > DirectMap2M:     2082816 kB
> > DirectMap1G:     2097152 kB
> >
> > At best, that's a bit confusing.  There aren't any other entries in
> > meminfo that occur more than once.  Plus, this information is available
> > in the sysfs interface.  Why isn't that sufficient?
> >
> > Could we do something where we keep the default hpage_size looking like
> > it does now, but append the size explicitly for the new entries?
> >
> > HugePages_Total(1G):       2
> > HugePages_Free(1G):        1
> > HugePages_Rsvd(1G):        1
> > HugePages_Surp(1G):        1
> >
>
> Let's not change the existing interface, please.
>
> Adding new fields: OK.
> Changing the way in whcih existing fields are calculated: OKish.
> Renaming existing fields: not OK.

How about lining up multiple values in each field like this?

  HugePages_Total:       5 2
  HugePages_Free:        2 1
  HugePages_Rsvd:        3 1
  HugePages_Surp:        1 1
  Hugepagesize:       2048 1048576 kB
  ...

This doesn't change the field names and the impact for user space
is still small?

Thanks,
Naoya
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