From: Hugh Dickins <hughd@google.com>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org
Subject: Re: [PATCH mmotm] thp: transparent hugepage core fixlet
Date: Mon, 10 Jan 2011 18:29:29 -0800 [thread overview]
Message-ID: <AANLkTin=gzZuDBMdGmR5ZY_9f6kggvt0KJA3XK33-z+2@mail.gmail.com> (raw)
In-Reply-To: <20110111015742.GL9506@random.random>
On Mon, Jan 10, 2011 at 5:57 PM, Andrea Arcangeli <aarcange@redhat.com> wrote:
> On Mon, Jan 10, 2011 at 04:55:53PM -0800, Hugh Dickins wrote:
>> If you configure THP in addition to HUGETLB_PAGE on x86_32 without PAE,
>> the p?d-folding works out that munlock_vma_pages_range() can crash to
>> follow_page()'s pud_huge() BUG_ON(flags & FOLL_GET): it needs the same
>> VM_HUGETLB check already there on the pmd_huge() line. Conveniently,
>> openSUSE provides a "blogd" which tests this out at startup!
>
> How is THP related to this? pud_trans_huge doesn't exist, if pud_huge
> is true, vma is already guaranteed to belong to hugetlbfs without
> requiring the additional check.
THP puts in pmds that are huge. In this configuration the "folding" is
such that the puds are the pmds. So the pud_huge test passes and
the BUG_ON hits. I hope I've explained that correctly, agreed that
it's confusing!
>
> I added the check to pmd_huge already, there it is needed, but for
> pud_huge it isn't as far as I can tell.
Crashing on that BUG_ON suggests otherwise ;)
Hugh
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next prev parent reply other threads:[~2011-01-11 2:29 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-11 0:55 Hugh Dickins
2011-01-11 1:57 ` Andrea Arcangeli
2011-01-11 2:29 ` Hugh Dickins [this message]
2011-01-11 14:04 ` Andrea Arcangeli
2011-01-11 16:31 ` Andrea Arcangeli
2011-01-11 22:59 ` Hugh Dickins
2011-01-12 2:02 ` Andrea Arcangeli
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