linux-kernel - Re: [RFC v2 0/2] add THP_HUGE_ZERO_PAGE

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Message-ID: <6lhepdol4nlnht7elb7jx7ot5hhckiegyyl6zeap2hmltdwb5t@ywsaklwnakuh>
Date: Thu, 22 May 2025 14:00:14 +0200
From: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: Pankaj Raghav <p.raghav@...sung.com>, 
	Suren Baghdasaryan <surenb@...gle.com>, Vlastimil Babka <vbabka@...e.cz>, 
	Ryan Roberts <ryan.roberts@....com>, Michal Hocko <mhocko@...e.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Nico Pache <npache@...hat.com>, Dev Jain <dev.jain@....com>, 
	Baolin Wang <baolin.wang@...ux.alibaba.com>, Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>, 
	"H . Peter Anvin" <hpa@...or.com>, Zi Yan <ziy@...dia.com>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, David Hildenbrand <david@...hat.com>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	"Liam R . Howlett" <Liam.Howlett@...cle.com>, Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org, 
	linux-fsdevel@...r.kernel.org, "Darrick J . Wong" <djwong@...nel.org>, gost.dev@...sung.com, 
	hch@....de, linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	willy@...radead.org, x86@...nel.org, mcgrof@...nel.org
Subject: Re: [RFC v2 0/2] add THP_HUGE_ZERO_PAGE_ALWAYS config option

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