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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20170928093955.lhwzkdqsshrhobnl@gmail.com>
Date:   Thu, 28 Sep 2017 11:39:55 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
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


* Kirill A. Shutemov <kirill@...temov.name> wrote:

> 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.

Ok, please put this information into the changelog, because it's relevant: we 
don't want to waste 2MB of RAM on the majority of systems that boot a distro 
kernel with 5-level paging enabled.

Thanks,

	Ingo