linux-kernel - Re: [PATCHv7 01/19] mm/sparsemem: Allocate mem_section at runtime for SPARSEMEM

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Date:   Thu, 28 Sep 2017 12:08:50 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Borislav Petkov <bp@...e.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv7 01/19] mm/sparsemem: Allocate mem_section at runtime
 for SPARSEMEM_EXTREME

On Thu, Sep 28, 2017 at 10:07:11AM +0200, Ingo Molnar wrote:
> 
> * Kirill A. Shutemov <kirill.shutemov@...ux.intel.com> wrote:
> 
> > Size of mem_section array depends on size of physical address space.
> > 
> > In preparation for boot-time switching between paging modes on x86-64
> > we need to make allocation of mem_section dynamic.
> > 
> > The patch allocates the array on the first call to
> > sparse_memory_present_with_active_regions().
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> 
> What is the size of the allocations here, in bytes, for the two main variants?

For 4-level paging it's 32k. For 5-level paging it's 2M.

-- 
 Kirill A. Shutemov