linux-kernel - Re: [PATCH] [BUGFIX] mm: hugepages can cause negative commitlimit

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Date:	Thu, 26 May 2011 18:07:53 -0300
From:	Rafael Aquini <aquini@...ux.com>
To:	Russ Anderson <rja@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH] [BUGFIX] mm: hugepages can cause negative commitlimit

On Fri, May 20, 2011 at 07:30:32PM -0300, Rafael Aquini wrote:
> On Fri, May 20, 2011 at 01:04:11PM -0700, Andrew Morton wrote:
> > On Thu, 19 May 2011 17:11:01 -0500
> > Russ Anderson <rja@....com> wrote:
> > 
> > > OK, I see your point.  The root problem is hugepages allocated at boot are
> > > subtracted from totalram_pages but hugepages allocated at run time are not.
> > > Correct me if I've mistate it or are other conditions.
> > > 
> > > By "allocated at run time" I mean "echo 1 > /proc/sys/vm/nr_hugepages".
> > > That allocation will not change totalram_pages but will change
> > > hugetlb_total_pages().
> > > 
> > > How best to fix this inconsistency?  Should totalram_pages include or exclude
> > > hugepages?  What are the implications?
> > 
> > The problem is that hugetlb_total_pages() is trying to account for two
> > different things, while totalram_pages accounts for only one of those
> > things, yes?
> > 
> > One fix would be to stop accounting for huge pages in totalram_pages
> > altogether.  That might break other things so careful checking would be
> > needed.
> > 
> > Or we stop accounting for the boot-time allocated huge pages in
> > hugetlb_total_pages().  Split the two things apart altogether and
> > account for boot-time allocated and runtime-allocated pages separately.  This
> > souds saner to me - it reflects what's actually happening in the kernel.
> 
> Perhaps we can just reinstate the # of pages "stealed" at early boot allocation
> later, when hugetlb_init() calls gather_bootmem_prealloc()
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 8ee3bd8..d606c9c 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1111,6 +1111,7 @@ static void __init gather_bootmem_prealloc(void)
>                 WARN_ON(page_count(page) != 1);
>                 prep_compound_huge_page(page, h->order);
>                 prep_new_huge_page(h, page, page_to_nid(page));
> +               totalram_pages += 1 << h->order;
>         }
>  }

Howdy Russ,

Were you able to confirm if that proposed change fix the issue you've reported?

Although I've tested it with usual size hugepages and it did not messed things up,
I'm not able to test it with GB hugepages, as I do not have any proc with "pdpe1gb" flag available.

Thanks in advance!
Cheers!
-- 
Rafael Aquini <aquini@...ux.com>
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