RE: [PATCH v2] X86-32: Allocate 256 bytes for pgd in PAE paging

[Yu, Fenghua]

> Sent: Thursday, December 18, 2014 9:26 AM
> To: Yu, Fenghua; Thomas Gleixner; H. Peter Anvin; Ingo Molnar; Williamson,
> Glenn P
> Cc: linux-kernel; x86
> Subject: Re: [PATCH v2] X86-32: Allocate 256 bytes for pgd in PAE paging
> 
> On 12/17/2014 01:47 PM, Fenghua Yu wrote:
> > From: Fenghua Yu <fenghua.yu@xxxxxxxxx>
> >
> > X86 32-bit machine and kernel use PAE paging, which currently wastes
> > about 4K of memory per process on Linux where we have to reserve an
> > entire page to support a single 256-byte PGD structure.  It would be a
> > very good thing if we could eliminate that wastage.
> >
> 
> 4*8 = 32 bytes, where did 256 bytes come from?

You are right. It should be 32 bytes. I will change the wording in future patch. The real calculation in code is right though.

Thanks.

-Fenghua
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