Re: [PATCH v5 09/11] thp: lazy huge zero page allocation

Kirill A. Shutemov
2012-11-15T09:41:19Z

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On Wed, Nov 14, 2012 at 03:37:09PM -0800, David Rientjes wrote:
> On Wed, 7 Nov 2012, Kirill A. Shutemov wrote:
>
> > From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> >
> > Instead of allocating huge zero page on hugepage_init() we can postpone it
> > until first huge zero page map. It saves memory if THP is not in use.
> >
>
> Is it worth the branch on every non-write pagefault after that? The
> unlikely() is not going to help on x86. If thp is enabled in your
> .config (which isn't the default), then I think it's better to just
> allocate the zero huge page once and avoid any branches after that to
> lazily allocate it. (Or do it only when thp is set to "madvise" or
> "always" if booting with transparent_hugepage=never.)

I can rewrite the check to static_key if you want. Would it be better?

--
Kirill A. Shutemov

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