Re: mm: VM_BUG_ON_PAGE(PageTail(page)) in mbind

From	Andrew Morton <akpm@linux-foundation.org>
Newsgroups	linux.kernel
Subject	Re: mm: VM_BUG_ON_PAGE(PageTail(page)) in mbind
Date	2016-01-26 21:50 +0100
Message-ID	<qViIN-1ad-1@gated-at.bofh.it> (permalink)
References	<qVbo0-4eF-33@gated-at.bofh.it> <qVipt-Vs-25@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Tue, 26 Jan 2016 22:28:29 +0200 "Kirill A. Shutemov" <kirill@shutemov.name> wrote:

> The patch below fixes the issue for me, but this bug makes me wounder how
> many bugs like this we have in kernel... :-/
> 
> Looks like we are too permissive about which VMA is migratable:
> vma_migratable() filters out VMA by VM_IO and VM_PFNMAP.
> I think VM_DONTEXPAND also correlate with VMA which cannot be migrated.
> 
> $ git grep VM_DONTEXPAND drivers | grep -v '\(VM_IO\|VM_PFNMAN\)' | wc -l 
> 33
> 
> Hm.. :-|
> 
> It worth looking on them closely... And I wouldn't be surprised if some
> VMAs without all of these flags are not migratable too.
> 
> Sigh.. Any thoughts?

Sigh indeed.  I think that both VM_DONTEXPAND and VM_DONTDUMP are
pretty good signs that mbind() should not be mucking with this vma.  If
such a policy sometimes results in mbind failing to set a policy then
that's not a huge loss - something runs a bit slower maybe.

I mean, we only really expect mbind() to operate against regular old
anon/pagecache memory, yes?

Thread

mm: VM_BUG_ON_PAGE(PageTail(page)) in mbind Dmitry Vyukov <dvyukov@google.com> - 2016-01-26 14:00 +0100
  Re: mm: VM_BUG_ON_PAGE(PageTail(page)) in mbind "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-01-26 21:30 +0100
    Re: mm: VM_BUG_ON_PAGE(PageTail(page)) in mbind Andrew Morton <akpm@linux-foundation.org> - 2016-01-26 21:50 +0100
      Re: mm: VM_BUG_ON_PAGE(PageTail(page)) in mbind "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-01-26 22:10 +0100
    Re: mm: VM_BUG_ON_PAGE(PageTail(page)) in mbind Andrew Morton <akpm@linux-foundation.org> - 2016-01-26 21:50 +0100
      Re: mm: VM_BUG_ON_PAGE(PageTail(page)) in mbind "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-01-26 22:10 +0100
    Re: mm: VM_BUG_ON_PAGE(PageTail(page)) in mbind Vlastimil Babka <vbabka@suse.cz> - 2016-01-26 22:40 +0100

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