linux-kernel - Re: [PATCHv4 15/39] thp, mm: trigger bug in replace_page_cache

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Date:	Tue, 28 May 2013 15:53:28 +0300 (EEST)
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Dave Hansen <dave@...1.net>
Cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Hugh Dickins <hughd@...gle.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Hillf Danton <dhillf@...il.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 15/39] thp, mm: trigger bug in replace_page_cache_page()
 on THP

Dave Hansen wrote:
> On 05/11/2013 06:23 PM, Kirill A. Shutemov wrote:
> > From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> > 
> > replace_page_cache_page() is only used by FUSE. It's unlikely that we
> > will support THP in FUSE page cache any soon.
> > 
> > Let's pospone implemetation of THP handling in replace_page_cache_page()
> > until any will use it.
> ...
> > diff --git a/mm/filemap.c b/mm/filemap.c
> > index 657ce82..3a03426 100644
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -428,6 +428,8 @@ int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
> >  {
> >  	int error;
> >  
> > +	VM_BUG_ON(PageTransHuge(old));
> > +	VM_BUG_ON(PageTransHuge(new));
> >  	VM_BUG_ON(!PageLocked(old));
> >  	VM_BUG_ON(!PageLocked(new));
> >  	VM_BUG_ON(new->mapping);
> 
> The code calling replace_page_cache_page() has a bunch of fallback and
> error returning code.  It seems a little bit silly to bring the whole
> machine down when you could just WARN_ONCE() and return an error code
> like fuse already does:

What about:

	if (WARN_ONCE(PageTransHuge(old) || PageTransHuge(new),
		     "%s: unexpected huge page\n", __func__))
		return -EINVAL;

?

-- 
 Kirill A. Shutemov
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