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

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Message-ID: <00000141a7d2aa7b-e59f292a-746c-4f55-aa51-9fa060a7fbeb-000000@email.amazonses.com>
Date:	Fri, 11 Oct 2013 14:01:43 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
cc:	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

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.

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