From: "Oscar Salvador (SUSE)" <osalvador@kernel•org>
To: Muchun Song <muchun.song@linux•dev>
Cc: "David Hildenbrand (Arm)" <david@kernel•org>,
Muchun Song <songmuchun@bytedance•com>,
Andrew Morton <akpm@linux-foundation•org>,
Catalin Marinas <catalin.marinas@arm•com>,
Will Deacon <will@kernel•org>,
Palmer Dabbelt <palmer@dabbelt•com>,
Paul Walmsley <pjw@kernel•org>,
Huacai Chen <chenhuacai@kernel•org>,
Andreas Larsson <andreas@gaisler•com>,
"David S. Miller" <davem@davemloft•net>,
linux-mm@kvack•org, linux-kernel@vger•kernel.org,
linux-arm-kernel@lists•infradead.org,
linux-riscv@lists•infradead.org, loongarch@lists•linux.dev,
sparclinux@vger•kernel.org, Alexandre Ghiti <alex@ghiti•fr>,
Albert Ou <aou@eecs•berkeley.edu>,
WANG Xuerui <kernel@xen0n•name>, Lorenzo Stoakes <ljs@kernel•org>,
"Liam R. Howlett" <liam@infradead•org>,
Vlastimil Babka <vbabka@kernel•org>,
Mike Rapoport <rppt@kernel•org>,
Suren Baghdasaryan <surenb@google•com>,
Michal Hocko <mhocko@suse•com>
Subject: Re: [PATCH v3 1/5] mm/sparse-vmemmap: provide generic vmemmap_set_pmd() and vmemmap_check_pmd()
Date: Tue, 2 Jun 2026 06:40:24 +0200 [thread overview]
Message-ID: <ah5euKU9l3pP_8Ty@localhost.localdomain> (raw)
In-Reply-To: <0D4AF42F-37C5-4A76-9703-44ACC6374C48@linux.dev>
On Mon, Jun 01, 2026 at 08:37:42PM +0800, Muchun Song wrote:
>
>
> > On Jun 1, 2026, at 20:22, David Hildenbrand (Arm) <david@kernel•org> wrote:
> >
> > On 6/1/26 10:48, Muchun Song wrote:
> >> The two weak functions are currently no-ops on every architecture,
> >> forcing each platform that needs them to duplicate the same handful
> >> of lines. Provide a generic implementation:
> >>
> >> - vmemmap_set_pmd() simply sets a huge PMD with PAGE_KERNEL protection.
> >>
> >> - vmemmap_check_pmd() verifies that the PMD is present and leaf,
> >> then calls the existing vmemmap_verify() helper.
> >>
> >> Architectures that need special handling can continue to override the
> >> weak symbols; everyone else gets the standard version for free.
> >>
> >> Signed-off-by: Muchun Song <songmuchun@bytedance•com>
> >> ---
> >> v2->v3:
> >> - Replace BUG_ON() with WARN_ON_ONCE() in vmemmap_set_pmd()
> >> ---
> >> mm/sparse-vmemmap.c | 7 ++++++-
> >> 1 file changed, 6 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> >> index 112ccf9c71ca..99e2be39671b 100644
> >> --- a/mm/sparse-vmemmap.c
> >> +++ b/mm/sparse-vmemmap.c
> >> @@ -386,12 +386,17 @@ int __meminit vmemmap_populate_hvo(unsigned long addr, unsigned long end,
> >> void __weak __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
> >> unsigned long addr, unsigned long next)
> >> {
> >> + WARN_ON_ONCE(!pmd_set_huge(pmd, virt_to_phys(p), PAGE_KERNEL));
> >
> >
> > Not sure if a VM_WARN_ON_ONCE() would be appropriate. (then, we have to move the
> > pmd_set_huge() out of the statement).
>
> I think it might be better to keep WARN_ON_ONCE here. This way, we can still
> monitor for warnings in production while keeping the code simple.
IIRC there was a discussion about this some time ago, given the fact that quite
some people out there tend to have 'panic_on_warn', but then again, if we fail to
set a PMD here it means something pretty nasty happened, so I am ok with that.
--
Oscar Salvador
SUSE Labs
next prev parent reply other threads:[~2026-06-02 4:40 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-01 8:48 [PATCH v3 0/5] mm/sparse-vmemmap: Provide generic vmemmap_set_pmd() and vmemmap_check_pmd() Muchun Song
2026-06-01 8:48 ` [PATCH v3 1/5] mm/sparse-vmemmap: provide " Muchun Song
2026-06-01 12:22 ` David Hildenbrand (Arm)
2026-06-01 12:37 ` Muchun Song
2026-06-02 4:40 ` Oscar Salvador (SUSE) [this message]
2026-06-02 4:41 ` Oscar Salvador (SUSE)
2026-06-01 8:48 ` [PATCH v3 2/5] arm64/mm: drop vmemmap_pmd helpers and use generic code Muchun Song
2026-06-01 12:23 ` David Hildenbrand (Arm)
2026-06-02 4:42 ` Oscar Salvador (SUSE)
2026-06-01 8:48 ` [PATCH v3 3/5] riscv/mm: " Muchun Song
2026-06-01 12:23 ` David Hildenbrand (Arm)
2026-06-02 4:44 ` Oscar Salvador (SUSE)
2026-06-01 8:48 ` [PATCH v3 4/5] loongarch/mm: drop vmemmap_check_pmd helper " Muchun Song
2026-06-01 12:24 ` David Hildenbrand (Arm)
2026-06-01 12:26 ` Muchun Song
2026-06-02 4:45 ` Oscar Salvador (SUSE)
2026-06-01 8:48 ` [PATCH v3 5/5] sparc/mm: " Muchun Song
2026-06-01 12:25 ` David Hildenbrand (Arm)
2026-06-02 4:46 ` Oscar Salvador (SUSE)
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