On Thu, Feb 27, 2025 at 9:56 AM Frank van der Linden <fvdl@xxxxxxxxxx> wrote: > > On Thu, Feb 27, 2025 at 9:32 AM Frank van der Linden <fvdl@xxxxxxxxxx> wrote: > > > > On Thu, Feb 27, 2025 at 9:20 AM Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > > > > > > On Thu, Feb 27, 2025 at 08:47:18AM -0800, Frank van der Linden wrote: > > > > On Wed, Feb 26, 2025 at 10:09 AM Johannes Weiner <hannes@xxxxxxxxxxx> 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: > > > > > > Thanks for the quick reply! > > > > > > > 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. > > > > > > That makes sense. > > > > > > But if it's infra code for a hugetlb feature, it should either be > > > something that HUGETLB_PAGE_OPTIMIZE_VMEMMAP pulls in automatically, > > > or at least be a hugetlb-specific option that pulls it in. > > > > > > Keep in mind that not everybody enables HUGETLBFS. In fact, hugetlb is > > > default N. It's moot to ask users whether they want to enable infra > > > code for a feature they aren't using, and default to Y no less. You're > > > regressing innocent bystanders doing this. > > > > The main reason that I added a separate config was: > > > > 1) I could see other subsystems use this. > > 2) The number of section flags is limited, so I wanted to put the one > > I added inside an option instead of always using it. > > > > If especially 2) is not a concern or can be solved differently, I'll > > be happy to remove the option. I don't particularly like having it, > > but I didn't see a better way. > > > > Let me think of a way to clean this up a little, and suggestions are > > welcome, of course. > > > > - Frank > > I'll just do: > > diff --git a/fs/Kconfig b/fs/Kconfig > index 64d420e3c475..fb9831927a08 100644 > --- a/fs/Kconfig > +++ b/fs/Kconfig > @@ -286,6 +286,7 @@ config HUGETLB_PAGE_OPTIMIZE_VMEMMAP > def_bool HUGETLB_PAGE > depends on ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP > depends on SPARSEMEM_VMEMMAP > + select SPARSEMEM_VMEMMAP_PREINIT > > config HUGETLB_PMD_PAGE_TABLE_SHARING > def_bool HUGETLB_PAGE > diff --git a/mm/Kconfig b/mm/Kconfig > index f984dd928ce7..44b52f8e5296 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -496,7 +496,6 @@ config ARCH_WANT_SPARSEMEM_VMEMMAP_PREINIT > config SPARSEMEM_VMEMMAP_PREINIT > bool "Early init of sparse memory virtual memmap" > depends on SPARSEMEM_VMEMMAP && ARCH_WANT_SPARSEMEM_VMEMMAP_PREINIT > - default y > > Does that seem ok? I'll send an mm-unstable follow-up patch. > Wait, that's actually not correct. Anyway, I'll stop spamming - I'll do it along these lines but properly, and will send a follow-up patch. - Frank
