linux-kernel - Re: [PATCH 2/4] mremap: don't do mm_populate(new

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Date:	Thu, 2 Jul 2015 00:41:54 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Hugh Dickins <hughd@...gle.com>,
	Jeff Moyer <jmoyer@...hat.com>,
	Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] mremap: don't do mm_populate(new_addr) on failure

On 07/01, David Rientjes wrote:
>
> On Sat, 20 Jun 2015, Oleg Nesterov wrote:
>
> > move_vma() sets *locked even if move_page_tables() or ->mremap()
> > fails, change sys_mremap() to check "ret & ~PAGE_MASK".
> >
> > I think we should simply remove the VM_LOCKED code in move_vma(),
> > that is why this patch doesn't change move_vma(). But this needs
> > more cleanups.
> >
> > Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> > ---
> >  mm/mremap.c |    4 +++-
> >  1 files changed, 3 insertions(+), 1 deletions(-)
> >
> > diff --git a/mm/mremap.c b/mm/mremap.c
> > index a6306bc..492721c 100644
> > --- a/mm/mremap.c
> > +++ b/mm/mremap.c
> > @@ -574,8 +574,10 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
> >  		ret = move_vma(vma, addr, old_len, new_len, new_addr, &locked);
> >  	}
> >  out:
> > -	if (ret & ~PAGE_MASK)
> > +	if (ret & ~PAGE_MASK) {
> >  		vm_unacct_memory(charged);
> > +		locked = 0;
> > +	}
> >  	up_write(&current->mm->mmap_sem);
> >  	if (locked && new_len > old_len)
> >  		mm_populate(new_addr + old_len, new_len - old_len);
>
> Acked-by: David Rientjes <rientjes@...gle.com>

Thanks! I am resending this series with your acks applies.

Plus another patche which was already acked but ignored anyway ;)

> Might be cleaner to rename this to "populate" in sys_mremap() and set it
> to false in the previous old_len >= new_len conditional and remove the
> check here for new_len > old_len.

Oh, this needs much more cleanups. Imo the whole VM_LOCKED logic in these
paths is ugly and confusing. move_vma() shouldn't look at VM_LOCKED at all,
mremap_to() should not duplicate the vma_to_resize/move_vma code, etc.

Oleg.

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