From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Sasha Levin <sasha.levin@oracle.com>,
Hugh Dickins <hughd@google.com>, Dave Jones <davej@redhat.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Linux Kernel <linux-kernel@vger.kernel.org>,
Rik van Riel <riel@redhat.com>, Ingo Molnar <mingo@redhat.com>,
Michel Lespinasse <walken@google.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Mel Gorman <mgorman@suse.de>
Subject: Re: pipe/page fault oddness.
Date: Thu, 2 Oct 2014 17:25:03 +0300 [thread overview]
Message-ID: <20141002142503.GA13203@node.dhcp.inet.fi> (raw)
In-Reply-To: <CA+55aFy7Y+pmhyEHTJg=K8gLKzLHxzz6j9FBJMt7_Fazfong6g@mail.gmail.com>
On Wed, Oct 01, 2014 at 03:42:53PM -0700, Linus Torvalds wrote:
> On Wed, Oct 1, 2014 at 3:08 PM, Sasha Levin <sasha.levin@oracle.com> wrote:
> >
> > I've tried this patch on the same configuration that was triggering
> > the VM_BUG_ON that Hugh mentioned previously. Surprisingly enough it
> > ran fine for ~20 minutes before exploding with:
>
> Well, that's somewhat encouraging. I didn't expect it to be perfect.
>
> That said, "ran fine" isn't necessarily the same thing as "worked".
> Who knows how buggy it was without showing overt symptoms until the
> BUG_ON() triggered. But hey, I'll be optimistic.
>
> > [ 2781.566206] kernel BUG at mm/huge_memory.c:1293!
>
> So that's
>
> BUG_ON(is_huge_zero_page(page));
>
> and the reason is trivial: the old code used to have a magical special
> case for the zero-page hugepage (see change_huge_pmd()) and I got rid
> of that (because now it's just about setting protections, and the
> zero-page hugepage is in no way special.
>
> So I think the solution is equally trivial: just accept that the
> zero-page can happen, and ignore it (just un-numa it).
>
> Appended is a incremental diff on top of the previous one. Even less
> tested than the last case, but I think you get the idea if it doesn't
> work as-is.
>
> Linus
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 14de54af6c38..fc33952d59c4 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1290,7 +1290,9 @@ int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
> }
>
> page = pmd_page(pmd);
> - BUG_ON(is_huge_zero_page(page));
> + if (is_huge_zero_page(page))
> + goto huge_zero_page;
> +
> page_nid = page_to_nid(page);
> last_cpupid = page_cpupid_last(page);
> count_vm_numa_event(NUMA_HINT_FAULTS);
> @@ -1381,6 +1383,11 @@ out:
> task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR, flags);
>
> return 0;
> +huge_zero_page:
> + pmd = pmd_modify(pmd, vma->vm_page_prot);
> + set_pmd_at(mm, haddr, pmdp, pmd);
> + update_mmu_cache_pmd(vma, addr, pmdp);
> + goto out_unlock;
I don't see what prevents the code to make zero page writable here.
We need at least pmd = pmd_wrprotect(pmd) before set_pmd_at();
--
Kirill A. Shutemov
next prev parent reply other threads:[~2014-10-02 14:25 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-30 3:33 pipe/page fault oddness Dave Jones
2014-09-30 4:27 ` Linus Torvalds
2014-09-30 4:33 ` Dave Jones
[not found] ` <CA+55aFwxdOBKHwwp7Zq1k19mHCyHYmYqigCVt59AtB-P7Zva1w@mail.gmail.com>
2014-09-30 15:52 ` Linus Torvalds
2014-09-30 16:03 ` Rik van Riel
2014-09-30 16:07 ` Dave Jones
2014-09-30 16:26 ` Linus Torvalds
2014-09-30 16:05 ` Dave Jones
2014-09-30 16:10 ` Linus Torvalds
2014-09-30 16:22 ` Dave Jones
2014-09-30 16:40 ` Dave Jones
2014-09-30 16:46 ` Linus Torvalds
2014-09-30 18:20 ` Dave Jones
2014-09-30 18:58 ` Linus Torvalds
2014-10-01 8:19 ` Hugh Dickins
2014-10-01 16:01 ` Linus Torvalds
2014-10-01 16:18 ` Linus Torvalds
2014-10-01 17:29 ` Rik van Riel
2014-10-02 8:28 ` Peter Zijlstra
2014-10-01 20:20 ` Linus Torvalds
2014-10-01 21:09 ` Rik van Riel
2014-10-01 22:08 ` Sasha Levin
2014-10-01 22:28 ` Chuck Ebbert
2014-10-02 3:32 ` Sasha Levin
2014-10-02 8:03 ` Chuck Ebbert
2014-10-02 14:49 ` Sasha Levin
2014-10-01 22:42 ` Linus Torvalds
2014-10-02 14:25 ` Kirill A. Shutemov [this message]
2014-10-02 16:01 ` Linus Torvalds
2014-10-02 16:35 ` Kirill A. Shutemov
2014-10-02 15:04 ` Sasha Levin
2014-10-02 16:10 ` Linus Torvalds
2014-10-03 5:00 ` Sasha Levin
2014-10-03 15:43 ` Linus Torvalds
2014-10-03 15:58 ` Dave Jones
2014-10-03 16:02 ` Sasha Levin
2014-10-02 12:45 ` Mel Gorman
2014-10-06 19:18 ` Aneesh Kumar K.V
2014-10-07 12:45 ` Linus Torvalds
2014-10-08 10:37 ` Aneesh Kumar K.V
2014-10-02 8:47 ` Hugh Dickins
2014-10-02 15:57 ` Linus Torvalds
2014-09-30 4:35 ` Al Viro
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