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Date: Wed, 29 Sep 2021 15:27:18 -0700
From: Mike Rapoport <rppt@kernel.org>
To: Nathan Chancellor <nathan@kernel.org>
Cc: Zhenguo Yao <yaozhenguo1@gmail.com>, mike.kravetz@oracle.com,
	mpe@ellerman.id.au, benh@kernel.crashing.org, paulus@samba.org,
	corbet@lwn.net, akpm@linux-foundation.org, yaozhenguo@jd.com,
	willy@infradead.org, linux-kernel@vger.kernel.org,
	linux-doc@vger.kernel.org, linux-mm@kvack.org, llvm@lists.linux.dev
Subject: Re: [PATCH v7] hugetlbfs: Extend the definition of hugepages
 parameter to support node allocation
Message-ID: <YVToRpjbg5mO0bru@kernel.org>
References: <20210927104149.46884-1-yaozhenguo1@gmail.com>
 <YVS9VhrAuKE2YdbF@archlinux-ax161>
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In-Reply-To: <YVS9VhrAuKE2YdbF@archlinux-ax161>

On Wed, Sep 29, 2021 at 12:24:06PM -0700, Nathan Chancellor wrote:
> On Mon, Sep 27, 2021 at 06:41:49PM +0800, Zhenguo Yao wrote:
> > We can specify the number of hugepages to allocate at boot. But the
> > hugepages is balanced in all nodes at present. In some scenarios,
> > we only need hugepages in one node. For example: DPDK needs hugepages
> > which are in the same node as NIC. if DPDK needs four hugepages of 1G
> > size in node1 and system has 16 numa nodes. We must reserve 64 hugepages
> > in kernel cmdline. But, only four hugepages are used. The others should
> > be free after boot. If the system memory is low(for example: 64G), it will
> > be an impossible task. So, Extending hugepages parameter to support
> > specifying hugepages at a specific node.
> > For example add following parameter:
> > 
> > hugepagesz=1G hugepages=0:1,1:3
> > 
> > It will allocate 1 hugepage in node0 and 3 hugepages in node1.
> > 
> > Signed-off-by: Zhenguo Yao <yaozhenguo1@gmail.com>
> 
> <snip>
> 
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index 95dc7b83381f..ca00676a1bdd 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -66,6 +66,7 @@ static struct hstate * __initdata parsed_hstate;
> >  static unsigned long __initdata default_hstate_max_huge_pages;
> >  static bool __initdata parsed_valid_hugepagesz = true;
> >  static bool __initdata parsed_default_hugepagesz;
> > +static unsigned int default_hugepages_in_node[MAX_NUMNODES] __initdata;
> >  
> >  /*
> >   * Protects updates to hugepage_freelists, hugepage_activelist, nr_huge_pages,
> > @@ -2868,33 +2869,41 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
> >  	return ERR_PTR(-ENOSPC);
> >  }
> >  
> > -int alloc_bootmem_huge_page(struct hstate *h)
> > +int alloc_bootmem_huge_page(struct hstate *h, int nid)
> >  	__attribute__ ((weak, alias("__alloc_bootmem_huge_page")));
> > -int __alloc_bootmem_huge_page(struct hstate *h)
> > +int __alloc_bootmem_huge_page(struct hstate *h, int nid)
> >  {
> >  	struct huge_bootmem_page *m;
> >  	int nr_nodes, node;
> >  
> > +	if (nid >= nr_online_nodes)
> > +		return 0;
> > +	/* do node specific alloc */
> > +	if (nid != NUMA_NO_NODE) {
> > +		m = memblock_alloc_try_nid_raw(huge_page_size(h), huge_page_size(h),
> > +				0, MEMBLOCK_ALLOC_ACCESSIBLE, nid);
> > +		if (m)
> > +			goto found;
> > +		else
> > +			return 0;
> > +	}
> > +	/* do all node balanced alloc */
> >  	for_each_node_mask_to_alloc(h, nr_nodes, node, &node_states[N_MEMORY]) {
> > -		void *addr;
> > -
> > -		addr = memblock_alloc_try_nid_raw(
> > +		m = memblock_alloc_try_nid_raw(
> >  				huge_page_size(h), huge_page_size(h),
> >  				0, MEMBLOCK_ALLOC_ACCESSIBLE, node);
> > -		if (addr) {
> > -			/*
> > -			 * Use the beginning of the huge page to store the
> > -			 * huge_bootmem_page struct (until gather_bootmem
> > -			 * puts them into the mem_map).
> > -			 */
> > -			m = addr;
> > +		/*
> > +		 * Use the beginning of the huge page to store the
> > +		 * huge_bootmem_page struct (until gather_bootmem
> > +		 * puts them into the mem_map).
> > +		 */
> > +		if (m)
> >  			goto found;
> > -		}
> > +		else
> > +			return 0;
> >  	}
> > -	return 0;
> >  
> >  found:
> > -	BUG_ON(!IS_ALIGNED(virt_to_phys(m), huge_page_size(h)));
> >  	/* Put them into a private list first because mem_map is not up yet */
> >  	INIT_LIST_HEAD(&m->list);
> >  	list_add(&m->list, &huge_boot_pages);
> 
> This hunk causes a clang warning now:
> 
> mm/hugetlb.c:2957:33: error: variable 'm' is used uninitialized whenever '&&' condition is false [-Werror,-Wsometimes-uninitialized]
>         for_each_node_mask_to_alloc(h, nr_nodes, node, &node_states[N_MEMORY]) {
>         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> mm/hugetlb.c:1254:3: note: expanded from macro 'for_each_node_mask_to_alloc'
>                 nr_nodes > 0 &&                                         \
>                 ^~~~~~~~~~~~
> mm/hugetlb.c:2974:18: note: uninitialized use occurs here
>         INIT_LIST_HEAD(&m->list);
>                         ^
> mm/hugetlb.c:2957:33: note: remove the '&&' if its condition is always true
>         for_each_node_mask_to_alloc(h, nr_nodes, node, &node_states[N_MEMORY]) {
>                                        ^
> mm/hugetlb.c:2942:29: note: initialize the variable 'm' to silence this warning
>         struct huge_bootmem_page *m;
>                                    ^
>                                     = NULL
> 1 error generated.
> 
> I am not sure if it is possible for nr_nodes to be 0 right out of the
> gate so might be a false positive?

With nr_nodes == 0 there will be no memory in the system :)

-- 
Sincerely yours,
Mike.