linux-kernel - Re: [PATCH v4 10/27] mm/sparse: allow for alternate vmemmap section init at boot

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: <CAPTztWaXZE=y4HBd7ZYW-1pTDrwxO3OBbwNJyu9vpuy22xx16A@mail.gmail.com>
Date: Thu, 27 Feb 2025 08:47:18 -0800
From: Frank van der Linden <fvdl@...gle.com>
To: Johannes Weiner <hannes@...xchg.org>
Cc: akpm@...ux-foundation.org, muchun.song@...ux.dev, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, yuzhao@...gle.com, usamaarif642@...il.com, 
	joao.m.martins@...cle.com, roman.gushchin@...ux.dev
Subject: Re: [PATCH v4 10/27] mm/sparse: allow for alternate vmemmap section
 init at boot

On Wed, Feb 26, 2025 at 10:09 AM Johannes Weiner <hannes@...xchg.org> wrote:
>
> On Tue, Feb 18, 2025 at 06:16:38PM +0000, Frank van der Linden wrote:
> > @@ -489,6 +489,14 @@ config SPARSEMEM_VMEMMAP
> >         SPARSEMEM_VMEMMAP uses a virtually mapped memmap to optimise
> >         pfn_to_page and page_to_pfn operations.  This is the most
> >         efficient option when sufficient kernel resources are available.
> > +
> > +config ARCH_WANT_SPARSEMEM_VMEMMAP_PREINIT
> > +     bool
> > +
> > +config SPARSEMEM_VMEMMAP_PREINIT
> > +     bool "Early init of sparse memory virtual memmap"
> > +     depends on SPARSEMEM_VMEMMAP && ARCH_WANT_SPARSEMEM_VMEMMAP_PREINIT
> > +     default y
>
> oldconfig just prompted me on this, but it's not clear to me what it
> does. Not even after skimming the changelog of the patch to be honest.
>
> Can you please add a help text that explains the user-visible effects
> of the toggle, as well as guidance as to who might care to change it?

Hi Johannes,

Thanks for your comment. How's this:

==
Enables subsystems to pre-initialize memmap in their own way,
allowing for memory savings during boot. The HugeTLB code uses
this to initialize memmap for bootmem allocated gigantic hugepages
in a way that is done by HUGETLB_PAGE_OPTIMIZE_VMEMMAP. This
means saving this memory right away, instead of allocating it
first and then freeing it later. Not allocating these pages
at all during boot allows for specifying a bigger number of
hugepages on the kernel commandline on larger systems.
==

- Frank