Re: [PATCH 03/12] mm: page_alloc: move set_zone_contiguous() into mm_init.c

[Kefeng Wang]

On 2023/5/8 15:12, Huang, Ying wrote:
> Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> writes:
>
> > set_zone_contiguous() is only used in mm init/hotplug, and
> > clear_zone_contiguous() only used in hotplug, move them from
> > page_alloc.c to the more appropriate file.
> >
> > Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> > ---
> >   include/linux/memory_hotplug.h |  3 --
> >   mm/internal.h                  |  7 +++
> >   mm/mm_init.c                   | 74 +++++++++++++++++++++++++++++++
> >   mm/page_alloc.c                | 79 ----------------------------------
> >   4 files changed, 81 insertions(+), 82 deletions(-)
...
> >   
> > +/*
> > + * Check that the whole (or subset of) a pageblock given by the interval of
> > + * [start_pfn, end_pfn) is valid and within the same zone, before scanning it
> > + * with the migration of free compaction scanner.
> > + *
> > + * Return struct page pointer of start_pfn, or NULL if checks were not passed.
> > + *
> > + * It's possible on some configurations to have a setup like node0 node1 node0
> > + * i.e. it's possible that all pages within a zones range of pages do not
> > + * belong to a single zone. We assume that a border between node0 and node1
> > + * can occur within a single pageblock, but not a node0 node1 node0
> > + * interleaving within a single pageblock. It is therefore sufficient to check
> > + * the first and last page of a pageblock and avoid checking each individual
> > + * page in a pageblock.
> > + *
> > + * Note: the function may return non-NULL struct page even for a page block
> > + * which contains a memory hole (i.e. there is no physical memory for a subset
> > + * of the pfn range). For example, if the pageblock order is MAX_ORDER, which
> > + * will fall into 2 sub-sections, and the end pfn of the pageblock may be hole
> > + * even though the start pfn is online and valid. This should be safe most of
> > + * the time because struct pages are still initialized via init_unavailable_range()
> > + * and pfn walkers shouldn't touch any physical memory range for which they do
> > + * not recognize any specific metadata in struct pages.
> > + */
> > +struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
> > +				     unsigned long end_pfn, struct zone *zone)
>
> __pageblock_pfn_to_page() is also called by compaction code too (e.g.,
> isolate_freepages_range() -> pageblock_pfn_to_page() ->
> __pageblock_pfn_to_page()).
>
> So, it is used not only by initialization and hotplug?

I should drop the move of this function, thanks for your reminder.

> Best Regards,
> Huang, Ying