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Message-ID: <CAAWJmAYJdEJyybVgD7erzZgvwufZ8gSmP_FCohmZLYozbhbb3g@mail.gmail.com>
Date: Thu, 18 Dec 2025 19:02:38 +0800
From: Tao pilgrim <pilgrimtao@...il.com>
To: "David Hildenbrand (Red Hat)" <david@...nel.org>
Cc: davem@...emloft.net, andreas@...sler.com, akpm@...ux-foundation.org,
lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, vbabka@...e.cz,
rppt@...nel.org, surenb@...gle.com, mhocko@...e.com, kevin.brodsky@....com,
dave.hansen@...ux.intel.com, ziy@...dia.com, chengkaitao@...inos.cn,
willy@...radead.org, zhengqi.arch@...edance.com, sparclinux@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] sparc: Use vmemmap_populate_hugepages for vmemmap_populate
On Thu, Dec 18, 2025 at 4:44 PM David Hildenbrand (Red Hat)
<david@...nel.org> wrote:
>
> On 12/17/25 13:08, chengkaitao wrote:
> > From: Chengkaitao <chengkaitao@...inos.cn>
> >
> > 1. Added the vmemmap_false_pmd function to accommodate architectures
> > that do not support basepages.
> > 2. In the SPARC architecture, reimplemented vmemmap_populate using
> > vmemmap_populate_hugepages.
> >
> > Signed-off-by: Chengkaitao <chengkaitao@...inos.cn>
> > ---
> > arch/sparc/mm/init_64.c | 56 ++++++++++++++++-------------------------
> > include/linux/mm.h | 1 +
> > mm/sparse-vmemmap.c | 7 +++++-
> > 3 files changed, 28 insertions(+), 36 deletions(-)
> >
> > diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c
> > index df9f7c444c39..a80cdfa6ba98 100644
> > --- a/arch/sparc/mm/init_64.c
> > +++ b/arch/sparc/mm/init_64.c
> > @@ -5,7 +5,7 @@
> > * Copyright (C) 1996-1999 David S. Miller (davem@...p.rutgers.edu)
> > * Copyright (C) 1997-1999 Jakub Jelinek (jj@...site.mff.cuni.cz)
> > */
> > -
> > +
> > #include <linux/extable.h>
> > #include <linux/kernel.h>
> > #include <linux/sched.h>
> > @@ -2397,11 +2397,11 @@ void __init paging_init(void)
> > * work.
> > */
> > init_mm.pgd += ((shift) / (sizeof(pgd_t)));
> > -
> > +
> > memset(swapper_pg_dir, 0, sizeof(swapper_pg_dir));
> >
> > inherit_prom_mappings();
> > -
> > +
> > /* Ok, we can use our TLB miss and window trap handlers safely. */
> > setup_tba();
> >
>
> Bunch of unrelated changes that should not go in here.
This indeed contains some unrelated code changes and removal of
extra whitespace. These could be split into a separate patch,
but the new patch might be somewhat redundant, lol. If you'd
like me to proceed this way, please reply confirming.
> > @@ -2581,8 +2581,8 @@ unsigned long _PAGE_CACHE __read_mostly;
> > EXPORT_SYMBOL(_PAGE_CACHE);
> >
> > #ifdef CONFIG_SPARSEMEM_VMEMMAP
> > -int __meminit vmemmap_populate(unsigned long vstart, unsigned long vend,
> > - int node, struct vmem_altmap *altmap)
> > +void __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
> > + unsigned long addr, unsigned long next)
> > {
> > unsigned long pte_base;
> >
> > @@ -2595,39 +2595,25 @@ int __meminit vmemmap_populate(unsigned long vstart, unsigned long vend,
> >
> > pte_base |= _PAGE_PMD_HUGE;
> >
> > - vstart = vstart & PMD_MASK;
> > - vend = ALIGN(vend, PMD_SIZE);
> > - for (; vstart < vend; vstart += PMD_SIZE) {
> > - pgd_t *pgd = vmemmap_pgd_populate(vstart, node);
> > - unsigned long pte;
> > - p4d_t *p4d;
> > - pud_t *pud;
> > - pmd_t *pmd;
> > -
> > - if (!pgd)
> > - return -ENOMEM;
> > -
> > - p4d = vmemmap_p4d_populate(pgd, vstart, node);
> > - if (!p4d)
> > - return -ENOMEM;
> > -
> > - pud = vmemmap_pud_populate(p4d, vstart, node);
> > - if (!pud)
> > - return -ENOMEM;
> > -
> > - pmd = pmd_offset(pud, vstart);
> > - pte = pmd_val(*pmd);
> > - if (!(pte & _PAGE_VALID)) {
> > - void *block = vmemmap_alloc_block(PMD_SIZE, node);
> > + pmd_val(*pmd) = pte_base | __pa(p);
> > +}
> >
> > - if (!block)
> > - return -ENOMEM;
> > +bool __meminit vmemmap_false_pmd(pmd_t *pmd, int node)
> > +{
> > + return true;
> > +}
> >
> > - pmd_val(*pmd) = pte_base | __pa(block);
> > - }
> > - }
> > +int __meminit vmemmap_check_pmd(pmd_t *pmdp, int node,
> > + unsigned long addr, unsigned long next)
> > +{
> > + vmemmap_verify((pte_t *)pmdp, node, addr, next);
> > + return 1;
> > +}
> >
> > - return 0;
> > +int __meminit vmemmap_populate(unsigned long vstart, unsigned long vend,
> > + int node, struct vmem_altmap *altmap)
> > +{
> > + return vmemmap_populate_hugepages(vstart, vend, node, altmap);
> > }
> > #endif /* CONFIG_SPARSEMEM_VMEMMAP */
> >
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index 15076261d0c2..5e005b0f947d 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -4248,6 +4248,7 @@ void *vmemmap_alloc_block_buf(unsigned long size, int node,
> > void vmemmap_verify(pte_t *, int, unsigned long, unsigned long);
> > void vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
> > unsigned long addr, unsigned long next);
> > +bool vmemmap_false_pmd(pmd_t *pmd, int node);
> > int vmemmap_check_pmd(pmd_t *pmd, int node,
> > unsigned long addr, unsigned long next);
> > int vmemmap_populate_basepages(unsigned long start, unsigned long end,
> > diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> > index 37522d6cb398..bd54b8c6f56e 100644
> > --- a/mm/sparse-vmemmap.c
> > +++ b/mm/sparse-vmemmap.c
> > @@ -407,6 +407,11 @@ void __weak __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
> > {
> > }
> >
> > +bool __weak __meminit vmemmap_false_pmd(pmd_t *pmd, int node)
> > +{
> > + return 0;
> > +}
> > +
>
> Reading that function I have absolutely no clue what this is supposed to
> do. :)
>
> Also, why are you passing pmd+node when sparc ignores them completely
> and statically returns "true" ?
The pmd+node is indeed unnecessary. My original intention was
to provide convenience for future architecture extensions, but
upon reflection, this appears to be a case of over-engineering.
> If you can tell me what the semantics of that function should be, maybe
> we can come up with a more descriptive name.
In the SPARC architecture, the original vmemmap_populate
function does not retry with vmemmap_populate_basepages
after vmemmap_alloc_block fails. I suspect SPARC doesn't
support basepages, which is why we need to modify
vmemmap_populate_hugepages to provide an interface that
skips basepages handling.
--
Yours,
Kaitao Cheng
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