Re: [External] Re: [RFC 2/4] mm/memblock: Add hugepage_size member to struct memblock_region

From: Usama Arif
Date: Wed Jul 26 2023 - 11:02:28 EST



On 26/07/2023 12:01, Mike Rapoport wrote:
On Mon, Jul 24, 2023 at 02:46:42PM +0100, Usama Arif wrote:
This propagates the hugepage size from the memblock APIs
(memblock_alloc_try_nid_raw and memblock_alloc_range_nid)
so that it can be stored in struct memblock region. This does not
introduce any functional change and hugepage_size is not used in
this commit. It is just a setup for the next commit where huge_pagesize
is used to skip initialization of struct pages that will be freed later
when HVO is enabled.

Signed-off-by: Usama Arif <usama.arif@xxxxxxxxxxxxx>
---
arch/arm64/mm/kasan_init.c | 2 +-
arch/powerpc/platforms/pasemi/iommu.c | 2 +-
arch/powerpc/platforms/pseries/setup.c | 4 +-
arch/powerpc/sysdev/dart_iommu.c | 2 +-
include/linux/memblock.h | 8 ++-
mm/cma.c | 4 +-
mm/hugetlb.c | 6 +-
mm/memblock.c | 60 ++++++++++++--------
mm/mm_init.c | 2 +-
mm/sparse-vmemmap.c | 2 +-
tools/testing/memblock/tests/alloc_nid_api.c | 2 +-
11 files changed, 56 insertions(+), 38 deletions(-)


[ snip ]

diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index f71ff9f0ec81..bb8019540d73 100644
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -63,6 +63,7 @@ struct memblock_region {
#ifdef CONFIG_NUMA
int nid;
#endif
+ phys_addr_t hugepage_size;
};
/**
@@ -400,7 +401,8 @@ phys_addr_t memblock_phys_alloc_range(phys_addr_t size, phys_addr_t align,
phys_addr_t start, phys_addr_t end);
phys_addr_t memblock_alloc_range_nid(phys_addr_t size,
phys_addr_t align, phys_addr_t start,
- phys_addr_t end, int nid, bool exact_nid);
+ phys_addr_t end, int nid, bool exact_nid,
+ phys_addr_t hugepage_size);

Rather than adding yet another parameter to memblock_phys_alloc_range() we
can have an API that sets a flag on the reserved regions.
With this the hugetlb reservation code can set a flag when HVO is
enabled and memmap_init_reserved_pages() will skip regions with this flag
set.


Hi,

Thanks for the review.

I think you meant memblock_alloc_range_nid/memblock_alloc_try_nid_raw and not memblock_phys_alloc_range?

My initial approach was to use flags, but I think it looks worse than what I have done in this RFC (I have pushed the flags prototype at https://github.com/uarif1/linux/commits/flags_skip_prep_init_gigantic_HVO, top 4 commits for reference (the main difference is patch 2 and 4 from RFC)). The major points are (the bigger issue is in patch 4):

- (RFC vs flags patch 2 comparison) In the RFC, hugepage_size is propagated from memblock_alloc_try_nid_raw through function calls. When using flags, the "no_init" boolean is propogated from memblock_alloc_try_nid_raw through function calls until the region flags are available in memblock_add_range and the new MEMBLOCK_NOINIT flag is set. I think its a bit more tricky to introduce a new function to set the flag in the region AFTER the call to memblock_alloc_try_nid_raw has finished as the memblock_region can not be found.
So something (hugepage_size/flag information) still has to be propagated through function calls and a new argument needs to be added.

- (RFC vs flags patch 4 comparison) We can't skip initialization of the whole region, only the tail pages. We still need to initialize the HUGETLB_VMEMMAP_RESERVE_SIZE (PAGE_SIZE) struct pages for each gigantic page.
In the RFC, hugepage_size from patch 2 was used in the for loop in memmap_init_reserved_pages in patch 4 to reserve HUGETLB_VMEMMAP_RESERVE_SIZE struct pages for every hugepage_size. This looks very simple and not hacky.
If we use a flag, there are 2 ways to initialize the HUGETLB_VMEMMAP_RESERVE_SIZE struct pages per hugepage:

1. (implemented in github link patch 4) memmap_init_reserved_pages skips the region for initialization as you suggested, and then we initialize HUGETLB_VMEMMAP_RESERVE_SIZE struct pages per hugepage somewhere later (I did it in gather_bootmem_prealloc). When calling reserve_bootmem_region in gather_bootmem_prealloc, we need to skip early_page_uninitialised and this makes it look a bit hacky.

2. We initialize the HUGETLB_VMEMMAP_RESERVE_SIZE struct pages per hugepage in memmap_init_reserved_pages itself. As we have used a flag and havent passed hugepage_size, we need to get the gigantic page size somehow. There doesnt seem to be a nice way to determine the gigantic page size in that function which is architecture dependent. I think gigantic page size can be given by PAGE_SIZE << (PUD_SHIFT - PAGE_SHIFT), but not sure if this is ok for all architectures? If we can use PAGE_SIZE << (PUD_SHIFT - PAGE_SHIFT) it will look much better than point 1.

Both the RFC patches and the github flags implementation work, but I think RFC patches look much cleaner. If there is a strong preference for the the github patches I can send it to mailing list?

Thanks,
Usama


phys_addr_t memblock_phys_alloc_try_nid(phys_addr_t size, phys_addr_t align, int nid);
static __always_inline phys_addr_t memblock_phys_alloc(phys_addr_t size,
@@ -415,7 +417,7 @@ void *memblock_alloc_exact_nid_raw(phys_addr_t size, phys_addr_t align,
int nid);
void *memblock_alloc_try_nid_raw(phys_addr_t size, phys_addr_t align,
phys_addr_t min_addr, phys_addr_t max_addr,
- int nid);
+ int nid, phys_addr_t hugepage_size);
void *memblock_alloc_try_nid(phys_addr_t size, phys_addr_t align,
phys_addr_t min_addr, phys_addr_t max_addr,
int nid);
@@ -431,7 +433,7 @@ static inline void *memblock_alloc_raw(phys_addr_t size,
{
return memblock_alloc_try_nid_raw(size, align, MEMBLOCK_LOW_LIMIT,
MEMBLOCK_ALLOC_ACCESSIBLE,
- NUMA_NO_NODE);
+ NUMA_NO_NODE, 0);
}
static inline void *memblock_alloc_from(phys_addr_t size,