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From: Mike Kravetz <mike.kravetz@oracle.com>
To: Muchun Song <songmuchun@bytedance.com>,
	corbet@lwn.net, tglx@linutronix.de, mingo@redhat.com,
	bp@alien8.de, x86@kernel.org, hpa@zytor.com,
	dave.hansen@linux.intel.com, luto@kernel.org,
	peterz@infradead.org, viro@zeniv.linux.org.uk,
	akpm@linux-foundation.org, paulmck@kernel.org,
	mchehab+huawei@kernel.org, pawan.kumar.gupta@linux.intel.com,
	rdunlap@infradead.org, oneukum@suse.com,
	anshuman.khandual@arm.com, jroedel@suse.de,
	almasrymina@google.com, rientjes@google.com
Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org
Subject: Re: [RFC PATCH 05/24] mm/hugetlb: Introduce nr_free_vmemmap_pages in the struct hstate
Date: Wed, 30 Sep 2020 15:41:28 -0700	[thread overview]
Message-ID: <b2811679-cd90-4685-2284-64490e7dfb7e@oracle.com> (raw)
In-Reply-To: <20200915125947.26204-6-songmuchun@bytedance.com>

On 9/15/20 5:59 AM, Muchun Song wrote:
> If the size of hugetlb page is 2MB, we need 512 struct page structures
> (8 pages) to be associated with it. As far as I know, we only use the
> first 3 struct page structures and only read the compound_dtor members

Actually, the first 4 pages can be used if CONFIG_CGROUP_HUGETLB.
/*
 * Minimum page order trackable by hugetlb cgroup.
 * At least 4 pages are necessary for all the tracking information.
 * The second tail page (hpage[2]) is the fault usage cgroup.
 * The third tail page (hpage[3]) is the reservation usage cgroup.
 */
#define HUGETLB_CGROUP_MIN_ORDER        2

However, this still easily fits within the first page of struct page
structures.

> of the remaining struct page structures. For tail page, the value of
> compound_dtor is the same. So we can reuse first tail page. We map the
> virtual addresses of the remaining 6 tail pages to the first tail page,
> and then free these 6 pages. Therefore, we need to reserve at least 2
> pages as vmemmap areas.

I got confused the first time I read the above sentences.  Perhaps it
should be more explicit with something like:

For tail pages, the value of compound_dtor is the same. So we can reuse
first page of tail page structs. We map the virtual addresses of the
remaining 6 pages of tail page structs to the first tail page struct,
and then free these 6 pages. Therefore, we need to reserve at least 2
pages as vmemmap areas.

It still does not sound great, but hopefully avoids some confusion.
-- 
Mike Kravetz

> So we introduce a new nr_free_vmemmap_pages field in the hstate to
> indicate how many vmemmap pages associated with a hugetlb page that we
> can free to buddy system.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  include/linux/hugetlb.h |  3 +++
>  mm/hugetlb.c            | 35 +++++++++++++++++++++++++++++++++++
>  2 files changed, 38 insertions(+)
> 
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index d5cc5f802dd4..eed3dd3bd626 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -492,6 +492,9 @@ struct hstate {
>  	unsigned int nr_huge_pages_node[MAX_NUMNODES];
>  	unsigned int free_huge_pages_node[MAX_NUMNODES];
>  	unsigned int surplus_huge_pages_node[MAX_NUMNODES];
> +#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
> +	unsigned int nr_free_vmemmap_pages;
> +#endif
>  #ifdef CONFIG_CGROUP_HUGETLB
>  	/* cgroup control files */
>  	struct cftype cgroup_files_dfl[7];
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 81a41aa080a5..f1b2b733b49b 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1292,6 +1292,39 @@ static inline void destroy_compound_gigantic_page(struct page *page,
>  						unsigned int order) { }
>  #endif
>  
> +#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
> +#define RESERVE_VMEMMAP_NR	2U
> +
> +static inline unsigned int nr_free_vmemmap(struct hstate *h)
> +{
> +	return h->nr_free_vmemmap_pages;
> +}
> +
> +static void __init hugetlb_vmemmap_init(struct hstate *h)
> +{
> +	unsigned int order = huge_page_order(h);
> +	unsigned int vmemmap_pages;
> +
> +	vmemmap_pages = ((1 << order) * sizeof(struct page)) >> PAGE_SHIFT;
> +	/*
> +	 * The head page and the first tail page not free to buddy system,
> +	 * the others page will map to the first tail page. So there are
> +	 * (@vmemmap_pages - RESERVE_VMEMMAP_NR) pages can be freed.
> +	 */
> +	if (vmemmap_pages > RESERVE_VMEMMAP_NR)
> +		h->nr_free_vmemmap_pages = vmemmap_pages - RESERVE_VMEMMAP_NR;
> +	else
> +		h->nr_free_vmemmap_pages = 0;
> +
> +	pr_info("HugeTLB: can free %d vmemmap pages for %s\n",
> +		h->nr_free_vmemmap_pages, h->name);
> +}
> +#else
> +static inline void hugetlb_vmemmap_init(struct hstate *h)
> +{
> +}
> +#endif
> +
>  static void update_and_free_page(struct hstate *h, struct page *page)
>  {
>  	int i;
> @@ -3285,6 +3318,8 @@ void __init hugetlb_add_hstate(unsigned int order)
>  	snprintf(h->name, HSTATE_NAME_LEN, "hugepages-%lukB",
>  					huge_page_size(h)/1024);
>  
> +	hugetlb_vmemmap_init(h);
> +
>  	parsed_hstate = h;
>  }
>  
> 

  reply	other threads:[~2020-09-30 22:43 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-15 12:59 [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Muchun Song
2020-09-15 12:59 ` [RFC PATCH 01/24] mm/memory_hotplug: Move bootmem info registration API to bootmem_info.c Muchun Song
2020-09-29 22:46   ` Mike Kravetz
2020-09-15 12:59 ` [RFC PATCH 02/24] mm/memory_hotplug: Move {get,put}_page_bootmem() " Muchun Song
2020-09-29 23:30   ` Mike Kravetz
2020-09-15 12:59 ` [RFC PATCH 03/24] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
2020-09-16  2:13   ` Randy Dunlap
2020-09-29 23:41   ` Mike Kravetz
2020-09-30  2:56     ` [External] " Muchun Song
2020-09-15 12:59 ` [RFC PATCH 04/24] mm/hugetlb: Register bootmem info when CONFIG_HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
2020-09-15 12:59 ` [RFC PATCH 05/24] mm/hugetlb: Introduce nr_free_vmemmap_pages in the struct hstate Muchun Song
2020-09-30 22:41   ` Mike Kravetz [this message]
2020-10-01  2:57     ` [External] " Muchun Song
2020-09-15 12:59 ` [RFC PATCH 06/24] mm/hugetlb: Introduce pgtable allocation/freeing helpers Muchun Song
2020-09-15 12:59 ` [RFC PATCH 07/24] mm/hugetlb: Add freeing unused vmemmap pages support for x86 Muchun Song
2020-09-15 12:59 ` [RFC PATCH 08/24] mm/bootmem_info: Introduce {free,prepare}_vmemmap_page() Muchun Song
2020-09-15 12:59 ` [RFC PATCH 09/24] x86/mm: Introduce VMEMMAP_SIZE/VMEMMAP_END macro Muchun Song
2020-09-15 12:59 ` [RFC PATCH 10/24] mm/hugetlb: Free the vmemmap pages associated with each hugetlb page Muchun Song
2020-09-15 12:59 ` [RFC PATCH 11/24] mm/hugetlb: Add vmemmap_pmd_huge macro for x86 Muchun Song
2020-09-15 12:59 ` [RFC PATCH 12/24] mm/hugetlb: Defer freeing of hugetlb pages Muchun Song
2020-09-15 12:59 ` [RFC PATCH 13/24] mm/hugetlb: Allocate the vmemmap pages associated with each hugetlb page Muchun Song
2020-09-15 12:59 ` [RFC PATCH 14/24] mm/hugetlb: Introduce remap_huge_page_pmd_vmemmap helper Muchun Song
2020-09-15 12:59 ` [RFC PATCH 15/24] mm/hugetlb: Use PG_slab to indicate split pmd Muchun Song
2020-09-15 12:59 ` [RFC PATCH 16/24] mm/hugetlb: Support freeing vmemmap pages of gigantic page Muchun Song
2020-09-15 12:59 ` [RFC PATCH 17/24] mm/hugetlb: Add a BUILD_BUG_ON to check if struct page size is a power of two Muchun Song
2020-09-15 12:59 ` [RFC PATCH 18/24] mm/hugetlb: Clear PageHWPoison on the non-error memory page Muchun Song
2020-09-15 12:59 ` [RFC PATCH 19/24] mm/hugetlb: Flush work when dissolving hugetlb page Muchun Song
2020-09-15 12:59 ` [RFC PATCH 20/24] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap Muchun Song
2020-09-16  2:10   ` Randy Dunlap
2020-09-16  2:50     ` [External] " Muchun Song
2020-09-15 12:59 ` [RFC PATCH 21/24] mm/hugetlb: Merge pte to huge pmd only for gigantic page Muchun Song
2020-09-20  9:59   ` Muchun Song
2020-09-15 12:59 ` [RFC PATCH 22/24] mm/hugetlb: Implement vmemmap_pmd_mkhuge macro Muchun Song
2020-09-15 12:59 ` [RFC PATCH 23/24] mm/hugetlb: Gather discrete indexes of tail page Muchun Song
2020-09-15 12:59 ` [RFC PATCH 24/24] mm/hugetlb: Add BUILD_BUG_ON to catch invalid usage of tail struct page Muchun Song
2020-09-15 14:32 ` [RFC PATCH 00/24] mm/hugetlb: Free some vmemmap pages of hugetlb page Matthew Wilcox
2020-09-15 14:53   ` Dave Hansen
2020-09-15 15:28   ` [External] " Muchun Song
2020-09-15 15:42     ` Matthew Wilcox
2020-09-15 17:32       ` Muchun Song
2020-09-15 17:39         ` Matthew Wilcox
2020-09-15 18:03           ` Muchun Song
2020-09-15 18:15             ` Matthew Wilcox
2020-09-16  2:45               ` Muchun Song
2020-09-29 21:58 ` Mike Kravetz
2020-09-30  3:13   ` Matthew Wilcox
2020-10-07 21:12   ` Mike Kravetz
2020-10-09  4:13     ` [External] " Muchun Song

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