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

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Message-Id: <1611574637.k9njsi2um5.astroid@bobo.none>
Date:   Mon, 25 Jan 2021 21:37:52 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-mm@...ck.org
Cc:     Ding Tianhong <dingtianhong@...wei.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, Zefan Li <lizefan@...wei.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>
Subject: Re: [PATCH v10 11/12] mm/vmalloc: Hugepage vmalloc mappings

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@...il.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.

Thanks,
Nick