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

[Kirill A. Shutemov]

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@xxxxxxxxxxxxxxx>
> > 
> > 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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