RE: [PATCH v10 11/12] mm/vmalloc: Hugepage vmalloc mappings

Nicholas Piggin
2021-01-26T09:51:34Z

Excerpts from David Laight's message of January 25, 2021 10:24 pm:
> From: Christophe Leroy
>> Sent: 25 January 2021 09:15
>>
>> Le 24/01/2021 à 09:22, Nicholas Piggin a écrit :
>> > Support huge page vmalloc mappings. Config option HAVE_ARCH_HUGE_VMALLOC
>> > enables support on architectures that define HAVE_ARCH_HUGE_VMAP and
>> > supports PMD sized vmap mappings.
>> >
>> > vmalloc will attempt to allocate PMD-sized pages if allocating PMD size
>> > or larger, and fall back to small pages if that was unsuccessful.
>> >
>> > Architectures must ensure that any arch specific vmalloc allocations
>> > that require PAGE_SIZE mappings (e.g., module allocations vs strict
>> > module rwx) use the VM_NOHUGE flag to inhibit larger mappings.
>> >
>> > When hugepage vmalloc mappings are enabled in the next patch, this
>> > reduces TLB misses by nearly 30x on a `git diff` workload on a 2-node
>> > POWER9 (59,800 -> 2,100) and reduces CPU cycles by 0.54%.
>> >
>> > This can result in more internal fragmentation and memory overhead for a
>> > given allocation, an option nohugevmalloc is added to disable at boot.
>> >
>> > Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
>> > ---
>> > arch/Kconfig | 10 +++
>> > include/linux/vmalloc.h | 18 ++++
>> > mm/page_alloc.c | 5 +-
>> > mm/vmalloc.c | 192 ++++++++++++++++++++++++++++++----------
>> > 4 files changed, 177 insertions(+), 48 deletions(-)
>> >
>>
>> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
>> > index 0377e1d059e5..eef61e0f5170 100644
>> > --- a/mm/vmalloc.c
>> > +++ b/mm/vmalloc.c
>>
>> > @@ -2691,15 +2746,18 @@ EXPORT_SYMBOL_GPL(vmap_pfn);
>> > #endif /* CONFIG_VMAP_PFN */
>> >
>> > static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
>> > - pgprot_t prot, int node)
>> > + pgprot_t prot, unsigned int page_shift,
>> > + int node)
>> > {
>> > const gfp_t nested_gfp = (gfp_mask & GFP_RECLAIM_MASK) | __GFP_ZERO;
>> > - unsigned int nr_pages = get_vm_area_size(area) >> PAGE_SHIFT;
>> > - unsigned long array_size;
>> > - unsigned int i;
>> > + unsigned int page_order = page_shift - PAGE_SHIFT;
>> > + unsigned long addr = (unsigned long)area->addr;
>> > + unsigned long size = get_vm_area_size(area);
>> > + unsigned int nr_small_pages = size >> PAGE_SHIFT;
>> > struct page **pages;
>> > + unsigned int i;
>> >
>> > - array_size = (unsigned long)nr_pages * sizeof(struct page *);
>> > + array_size = (unsigned long)nr_small_pages * sizeof(struct page *);
>>
>> array_size() is a function in include/linux/overflow.h
>>
>> For some reason, it breaks the build with your series.
>
> I can't see the replacement definition for array_size.
> The old local variable is deleted.

Yeah I saw that after taking another look. Must have sent in a bad diff.
The v11 fixed that and a couple of other compile issues.

Thanks,
Nick