Re: [RFC v2 0/2] add THP_HUGE_ZERO_PAGE_ALWAYS config option

["Pankaj Raghav (Samsung)" <kernel@xxxxxxxxxxxxxxxx>]

Hi Mike,

> > Add a config option THP_HUGE_ZERO_PAGE_ALWAYS that will always allocate
> > the huge_zero_folio, and it will never be freed. This makes using the
> > huge_zero_folio without having to pass any mm struct and a call to put_folio
> > in the destructor.
> 
> I don't think this config option should be tied to THP. It's perfectly
> sensible to have a configuration with HUGETLB and without THP.
>  

Hmm, that makes sense. You mean something like this (untested):

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 2e1527580746..d447a9b9eb7d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -151,8 +151,8 @@ config X86
        select ARCH_WANT_OPTIMIZE_DAX_VMEMMAP   if X86_64
        select ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP       if X86_64
        select ARCH_WANT_HUGETLB_VMEMMAP_PREINIT if X86_64
+       select ARCH_WANTS_HUGE_ZERO_PAGE_ALWAYS if X86_64
        select ARCH_WANTS_THP_SWAP              if X86_64
-       select ARCH_WANTS_THP_ZERO_PAGE_ALWAYS  if X86_64
        select ARCH_HAS_PARANOID_L1D_FLUSH
        select BUILDTIME_TABLE_SORT
        select CLKEVT_I8253
diff --git a/mm/Kconfig b/mm/Kconfig
index a2994e7d55ba..83a5b95a2286 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -823,9 +823,19 @@ config ARCH_WANT_GENERAL_HUGETLB
 config ARCH_WANTS_THP_SWAP
        def_bool n
 
-config ARCH_WANTS_THP_ZERO_PAGE_ALWAYS
+config ARCH_WANTS_HUGE_ZERO_PAGE_ALWAYS
        def_bool n
 
+config HUGE_ZERO_PAGE_ALWAYS
+       def_bool y
+       depends on HUGETLB_PAGE && ARCH_WANTS_HUGE_ZERO_PAGE_ALWAYS
+       help
+         Typically huge_zero_folio, which is a huge page of zeroes, is allocated
+         on demand and deallocated when not in use. This option will always
+         allocate huge_zero_folio for zeroing and it is never deallocated.
+         Not suitable for memory constrained systems.
+
+
 config MM_ID
        def_bool n
 
@@ -898,15 +908,6 @@ config READ_ONLY_THP_FOR_FS
          support of file THPs will be developed in the next few release
          cycles.
 
-config THP_ZERO_PAGE_ALWAYS
-       def_bool y
-       depends on TRANSPARENT_HUGEPAGE && ARCH_WANTS_THP_ZERO_PAGE_ALWAYS
-       help
-         Typically huge_zero_folio, which is a THP of zeroes, is allocated
-         on demand and deallocated when not in use. This option will always
-         allocate huge_zero_folio for zeroing and it is never deallocated.
-         Not suitable for memory constrained systems.
-
 config NO_PAGE_MAPCOUNT
        bool "No per-page mapcount (EXPERIMENTAL)"
        help

--
Pankaj