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

Christophe Leroy
2021-01-25T12:20:19Z

Le 25/01/2021 à 12:37, Nicholas Piggin a écrit :
> Excerpts from Christophe Leroy's message of January 25, 2021 7:14 pm:
>>
>>
>> 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.
>
> What config? I haven't seen it.
>

Several configs I believe. I saw it this morning in
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20210124082230.2118861-13-npiggin@gmail.com/

Though the reports have all disappeared now.