linux-kernel - Re: [PATCH 34/34] mm: dynamically allocate page->ptl if it cannot be embedded to struct page

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Date:	Mon, 14 Oct 2013 12:04:37 +0300 (EEST)
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH 34/34] mm: dynamically allocate page->ptl if it cannot be
 embedded to struct page

Christoph Lameter wrote:
> On Thu, 10 Oct 2013, Kirill A. Shutemov wrote:
> 
> > Christoph Lameter wrote:
> > > On Thu, 10 Oct 2013, Kirill A. Shutemov wrote:
> > >
> > > > +static inline bool ptlock_alloc(struct page *page)
> > > > +{
> > > > +	if (sizeof(spinlock_t) > sizeof(page->ptl))
> > > > +		return __ptlock_alloc(page);
> > > > +	return true;
> > > > +}
> > >
> > > Could you make the check a CONFIG option? CONFIG_PTLOCK_DOES_NOT_FIT_IN_PAGE_STRUCT or
> > > so?
> >
> > No. We will have to track what affects sizeof(spinlock_t) manually.
> > Not a fun and error prune.
> 
> You can generate a config option depending on the size of the object via
> Kbuild. Kbuild will determine the setting before building the kernel as a
> whole by runing some small C program.

I don't think it's any better than what we have there now.

-- 
 Kirill A. Shutemov
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