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

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Message-ID: <a3b26f6e-6f33-a606-6d60-5671e5ee395f@csgroup.eu>
Date:   Mon, 25 Jan 2021 13:13:59 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Nicholas Piggin <npiggin@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, 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



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@...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.
> 

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.