Re: [PATCH v1] memblock: Initialized the memory of memblock.reserve to the MIGRATE_MOVABL

[Su Hua]

Hi Mike

Thanks for your advice and sorry for taking so long to reply.

I looked at the logic again. deferred_init_pages is currently used to
handle all (memory &&! reserved) area memblock，and put that memory in
buddy.
Change it to also handle reserved memory may involve more code
changes. I wonder if I can change the commit message: This patch is
mainly to
make the migration type to MIGRATE_MOVABLE when the reserve type page
is initialized, regardless of whether CONFIG_DEFERRED_STRUCT_PAGE_INIT
is set or not?

When not set CONFIG_DEFERRED_STRUCT_PAGE_INIT， initializes memblock of
reserve type to MIGRATE_MOVABLE by default at memmap_init initializes
memory.

Sincerely yours，
Su


Mike Rapoport <rppt@xxxxxxxxxx> 于2024年9月29日周日 17:18写道：
>
> On Wed, Sep 25, 2024 at 07:02:35PM +0800, suhua wrote:
> > After sparse_init function requests memory for struct page in memblock and
> > adds it to memblock.reserved, this memory area is present in both
> > memblock.memory and memblock.reserved.
> >
> > When CONFIG_DEFERRED_STRUCT_PAGE_INIT is not set. The memmap_init function
> > is called during the initialization of the free area of the zone, this
> > function calls for_each_mem_pfn_range to initialize all memblock.memory,
> > excluding memory that is also placed in memblock.reserved, such as the
> > struct page metadata that describes the page, 1TB memory is about 16GB,
> > and generally this part of reserved memory occupies more than 90% of the
> > total reserved memory of the system. So all memory in memblock.memory is
> > set to MIGRATE_MOVABLE according to the alignment of pageblock_nr_pages.
> > For example, if hugetlb_optimize_vmemmap=1, huge pages are allocated, the
> > freed pages are placed on buddy's MIGRATE_MOVABL list for use.
>
> Please make sure you spell MIGRATE_MOVABLE and MIGRATE_UNMOVABLE correctly.
>
> > When CONFIG_DEFERRED_STRUCT_PAGE_INIT=y, only the first_deferred_pfn range
> > is initialized in memmap_init. The subsequent free_low_memory_core_early
> > initializes all memblock.reserved memory but not MIGRATE_MOVABL. All
> > memblock.memory is set to MIGRATE_MOVABL when it is placed in buddy via
> > free_low_memory_core_early and deferred_init_memmap. As a result, when
> > hugetlb_optimize_vmemmap=1 and huge pages are allocated, the freed pages
> > will be placed on buddy's MIGRATE_UNMOVABL list (For example, on machines
> > with 1TB of memory, alloc 2MB huge page size of 1000GB frees up about 15GB
> > to MIGRATE_UNMOVABL). Since the huge page alloc requires a MIGRATE_MOVABL
> > page, a fallback is performed to alloc memory from MIGRATE_UNMOVABL for
> > MIGRATE_MOVABL.
> >
> > Large amount of UNMOVABL memory is not conducive to defragmentation, so
> > the reserved memory is also set to MIGRATE_MOVABLE in the
> > free_low_memory_core_early phase following the alignment of
> > pageblock_nr_pages.
> >
> > Eg：
> > echo 500000 > /proc/sys/vm/nr_hugepages
> > cat /proc/pagetypeinfo
> >
> > before：
> > Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
> > …
> > Node    0, zone   Normal, type    Unmovable     51      2      1     28     53     35     35     43     40     69   3852
> > Node    0, zone   Normal, type      Movable   6485   4610    666    202    200    185    208     87     54      2    240
> > Node    0, zone   Normal, type  Reclaimable      2      2      1     23     13      1      2      1      0      1      0
> > Node    0, zone   Normal, type   HighAtomic      0      0      0      0      0      0      0      0      0      0      0
> > Node    0, zone   Normal, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
> > Unmovable ≈ 15GB
> >
> > after：
> > Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
> > …
> > Node    0, zone   Normal, type    Unmovable      0      1      1      0      0      0      0      1      1      1      0
> > Node    0, zone   Normal, type      Movable   1563   4107   1119    189    256    368    286    132    109      4   3841
> > Node    0, zone   Normal, type  Reclaimable      2      2      1     23     13      1      2      1      0      1      0
> > Node    0, zone   Normal, type   HighAtomic      0      0      0      0      0      0      0      0      0      0      0
> > Node    0, zone   Normal, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
> >
> > Signed-off-by: suhua <suhua1@xxxxxxxxxxxx>
> > ---
> >  mm/mm_init.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/mm/mm_init.c b/mm/mm_init.c
> > index 4ba5607aaf19..e0190e3f8f26 100644
> > --- a/mm/mm_init.c
> > +++ b/mm/mm_init.c
> > @@ -722,6 +722,12 @@ static void __meminit init_reserved_page(unsigned long pfn, int nid)
> >               if (zone_spans_pfn(zone, pfn))
> >                       break;
> >       }
> > +
> > +     if (pageblock_aligned(pfn)) {
> > +             set_pageblock_migratetype(pfn_to_page(pfn), MIGRATE_MOVABLE);
> > +             cond_resched();
> > +     }
>
> If you are trying to make initialization of pageblock migrate type
> consistent with or without CONFIG_DEFERRED_STRUCT_PAGE_INIT, move setting
> of migrate type from deferred_free_pages() to deferred_init_pages().
>
> > +
> >       __init_single_page(pfn_to_page(pfn), pfn, zid, nid);
> >  }
> >  #else
> > --
> > 2.34.1
> >
>
> --
> Sincerely yours,
> Mike.