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
