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Muchun Song
48070b721a
Patch series "mm: Introduce section-based vmemmap optimization for
HugeTLB", v6.
This series is split out from the earlier, larger series "mm: Generalize
HVO for HugeTLB and device DAX" [1]. While the parent series generalizes
vmemmap optimization across HugeTLB and device DAX, this subset addresses
a single, self-contained step: making the generic sparse-vmemmap code
section-based optimization aware and switching HugeTLB bootmem pages to
this path.
HugeTLB vmemmap optimization currently has its own early boot setup path.
It pre-populates optimized vmemmap mappings before the normal
sparse-vmemmap population code runs, and sparsemem carries
SPARSEMEM_VMEMMAP_PREINIT only to support that special case.
That makes the HugeTLB vmemmap optimization path harder to share with
other users of sparse-vmemmap optimization and leaves a fair amount of
HugeTLB-specific boot-time state in the generic memory initialization
flow.
This series introduces section-based vmemmap optimization support in the
sparse-vmemmap code and switches HugeTLB bootmem pages over to it.
Instead of having HugeTLB pre-populate optimized vmemmap mappings itself,
HugeTLB now records the compound page order in the corresponding memory
sections. The generic sparse-vmemmap population path can then allocate or
reuse shared tail vmemmap pages based on section metadata.
The patches are organized as follows:
- patches 1-2 prepare sparsemem and vmemmap optimization metadata
- patches 3-8 teach the common sparse-vmemmap paths to use that state
- patches 9-10 switch HugeTLB bootmem optimization to the
section-based path
- patches 11-17 clean up sparsemem and HugeTLB bootmem code that is no
longer needed after the conversion
This is intended to be the second smaller step toward the broader HVO
generalization. The device DAX conversion and the wider HVO consolidation
are left for follow-up series.
This patch (of 17):
struct mem_section is currently forced to a power-of-2 size so the
section-to-root lookup can use a mask instead of a modulo.
That requirement makes future extensions harder than necessary: adding a
small field can require configuration-dependent padding or layout checks
just to preserve the lookup scheme. Keep the lookup correct for any
struct mem_section size by using a plain modulo instead.
Do not leave the layout entirely unconstrained, though. Keep struct
mem_section double-word aligned so modest size changes, such as adding
another word-sized field on 64-bit systems, still keep a compact and
efficient layout. If future fields grow the structure beyond that sweet
spot, the lookup remains correct; only the exact layout efficiency
changes.
Link: https://lore.kernel.org/20260910063256.64386-2-songmuchun@bytedance.com
Link: https://lore.kernel.org/all/20260513130542.35604-1-songmuchun@bytedance.com/ [1]
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: David Laight <david.laight.linux@gmail.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Qi Zheng <qi.zheng@linux.dev>