Re: [PATCH v2 4/5] mm/sparse-vmemmap: drop vmemmap_can_optimize()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] mm/vmemmap: undeclared vmemmap in section_vmemmap_optimization_disable()
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commit f0544b0eb7001e7264ebe693d049cf0cf0631ccd
Author: Muchun Song <muchun.song@linux.dev>

mm/sparse-vmemmap: drop vmemmap_can_optimize()

This commit removes the DAX-specific vmemmap_can_optimize() helper and relies
on section_vmemmap_optimizable() and section_vmemmap_optimization_disable()
to decide whether a section uses vmemmap optimization.

> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index a060a71504015..2fa5ce73b382a 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -38,7 +38,6 @@
>  #include <linux/bitops.h>
>  #include <linux/iommu-debug-pagealloc.h>
>  #include <linux/kcsan-checks.h>
> -#include <linux/vmemmap-optimization.h>

[Severity: Low]
Does this cause a build regression on LoongArch 64-bit configurations with
CONFIG_VMEMMAP_OPTIMIZATION enabled (such as loongson64_defconfig), or when
linux/vmemmap-optimization.h is included before asm/pgtable.h defines
vmemmap?

In arch/loongarch/include/asm/pgtable.h, asm/page.h (which pulls in
include/asm-generic/memory_model.h) is included first, defining:

    #define __page_to_pfn(page)	(unsigned long)((page) - vmemmap)

Later in arch/loongarch/include/asm/pgtable.h, linux/vmemmap-optimization.h
is included so MAX_FOLIO_VMEMMAP_ALIGN is available before defining vmemmap:

    #include <linux/mm_types.h>
    #include <linux/mmzone.h>
    #include <linux/vmemmap-optimization.h>
    ...
    #define VMEMMAP_ALIGN	max(PMD_SIZE, MAX_FOLIO_VMEMMAP_ALIGN)
    #define vmemmap		((struct page *)(ALIGN(VMALLOC_END, VMEMMAP_ALIGN)))

Because section_vmemmap_optimization_disable() in
include/linux/vmemmap-optimization.h is a static inline function that calls
page_to_pfn():

    static inline void section_vmemmap_optimization_disable(unsigned long start,
            unsigned long end)
    {
        unsigned long pfn = page_to_pfn((struct page *)start);

the preprocessor expands page_to_pfn() at the point where
linux/vmemmap-optimization.h is included, before the vmemmap macro is
defined, leaving an undeclared vmemmap identifier in the function body.

Additionally, removing the linux/vmemmap-optimization.h include from
include/linux/mm.h (where it was placed after linux/pgtable.h) means any
translation unit that includes linux/vmemmap-optimization.h before
asm/pgtable.h on architectures where vmemmap is defined in asm/pgtable.h will
hit the same undeclared vmemmap error.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261105061217.13302-1-songmuchun@bytedance.com?part=4