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, willy@infradead.org,
osalvador@suse.de, mhocko@suse.com
Cc: duanxiongchun@bytedance.com, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v3 05/21] mm/hugetlb: Introduce pgtable allocation/freeing helpers
Date: Tue, 10 Nov 2020 16:47:03 -0800 [thread overview]
Message-ID: <9dc62874-379f-b126-94a7-5bd477529407@oracle.com> (raw)
In-Reply-To: <20201108141113.65450-6-songmuchun@bytedance.com>
On 11/8/20 6:10 AM, Muchun Song wrote:
> On x86_64, vmemmap is always PMD mapped if the machine has hugepages
> support and if we have 2MB contiguos pages and PMD aligned. If we want
> to free the unused vmemmap pages, we have to split the huge pmd firstly.
> So we should pre-allocate pgtable to split PMD to PTE.
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index a0007902fafb..5c7be2ee7e15 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1303,6 +1303,108 @@ static inline void destroy_compound_gigantic_page(struct page *page,
...
> +static inline void vmemmap_pgtable_init(struct page *page)
> +{
> + page_huge_pte(page) = NULL;
> +}
> +
> +static void vmemmap_pgtable_deposit(struct page *page, pgtable_t pgtable)
> +{
> + /* FIFO */
> + if (!page_huge_pte(page))
> + INIT_LIST_HEAD(&pgtable->lru);
> + else
> + list_add(&pgtable->lru, &page_huge_pte(page)->lru);
> + page_huge_pte(page) = pgtable;
> +}
> +
> +static pgtable_t vmemmap_pgtable_withdraw(struct page *page)
> +{
> + pgtable_t pgtable;
> +
> + /* FIFO */
> + pgtable = page_huge_pte(page);
> + page_huge_pte(page) = list_first_entry_or_null(&pgtable->lru,
> + struct page, lru);
> + if (page_huge_pte(page))
> + list_del(&pgtable->lru);
> + return pgtable;
> +}
> +
> +static int vmemmap_pgtable_prealloc(struct hstate *h, struct page *page)
> +{
> + int i;
> + pgtable_t pgtable;
> + unsigned int nr = pgtable_pages_to_prealloc_per_hpage(h);
> +
> + if (!nr)
> + return 0;
> +
> + vmemmap_pgtable_init(page);
> +
> + for (i = 0; i < nr; i++) {
> + pte_t *pte_p;
> +
> + pte_p = pte_alloc_one_kernel(&init_mm);
> + if (!pte_p)
> + goto out;
> + vmemmap_pgtable_deposit(page, virt_to_page(pte_p));
> + }
> +
> + return 0;
> +out:
> + while (i-- && (pgtable = vmemmap_pgtable_withdraw(page)))
> + pte_free_kernel(&init_mm, page_to_virt(pgtable));
> + return -ENOMEM;
> +}
> +
> +static void vmemmap_pgtable_free(struct hstate *h, struct page *page)
> +{
> + pgtable_t pgtable;
> + unsigned int nr = pgtable_pages_to_prealloc_per_hpage(h);
> +
> + if (!nr)
> + return;
> +
> + pgtable = page_huge_pte(page);
> + if (!pgtable)
> + return;
> +
> + while (nr-- && (pgtable = vmemmap_pgtable_withdraw(page)))
> + pte_free_kernel(&init_mm, page_to_virt(pgtable));
> +}
I may be confused.
In patch 9 of this series, the first call to vmemmap_pgtable_free() is made:
> @@ -1645,6 +1799,10 @@ void free_huge_page(struct page *page)
>
> static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
> {
> + free_huge_page_vmemmap(h, page);
> + /* Must be called before the initialization of @page->lru */
> + vmemmap_pgtable_free(h, page);
> +
> INIT_LIST_HEAD(&page->lru);
> set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
> set_hugetlb_cgroup(page, NULL);
When I saw that comment in previous patch series, I assumed page->lru was
being used to store preallocated pages and pages to free. However, unless
I am reading the code incorrectly it does not appear page->lru (of the huge
page) is being used for this purpose. Is that correct?
If it is correct, would using page->lru of the huge page make this code
simpler? I am just missing the reason why you are using
page_huge_pte(page)->lru
--
Mike Kravetz
next prev parent reply other threads:[~2020-11-11 0:48 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-08 14:10 [PATCH v3 00/21] Free some vmemmap pages of hugetlb page Muchun Song
2020-11-08 14:10 ` [PATCH v3 01/21] mm/memory_hotplug: Move bootmem info registration API to bootmem_info.c Muchun Song
2020-11-08 14:10 ` [PATCH v3 02/21] mm/memory_hotplug: Move {get,put}_page_bootmem() " Muchun Song
2020-11-08 14:10 ` [PATCH v3 03/21] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
2020-11-09 13:52 ` Oscar Salvador
2020-11-09 14:20 ` [External] " Muchun Song
2020-11-10 19:31 ` Mike Kravetz
2020-11-10 19:50 ` Matthew Wilcox
2020-11-10 20:30 ` Mike Kravetz
2020-11-17 15:35 ` [External] " Muchun Song
2020-11-11 3:28 ` Muchun Song
2020-11-08 14:10 ` [PATCH v3 04/21] mm/hugetlb: Introduce nr_free_vmemmap_pages in the struct hstate Muchun Song
2020-11-09 16:48 ` Oscar Salvador
2020-11-10 2:42 ` [External] " Muchun Song
2020-11-10 19:38 ` Mike Kravetz
2020-11-11 3:22 ` Muchun Song
2020-11-08 14:10 ` [PATCH v3 05/21] mm/hugetlb: Introduce pgtable allocation/freeing helpers Muchun Song
2020-11-09 17:21 ` Oscar Salvador
2020-11-10 3:49 ` [External] " Muchun Song
2020-11-10 5:42 ` Oscar Salvador
2020-11-10 6:08 ` Muchun Song
2020-11-10 6:33 ` Oscar Salvador
2020-11-10 7:10 ` Muchun Song
2020-11-11 0:47 ` Mike Kravetz [this message]
2020-11-11 3:41 ` Muchun Song
2020-11-13 0:35 ` Mike Kravetz
2020-11-13 1:02 ` Mike Kravetz
2020-11-13 4:18 ` Muchun Song
2020-11-08 14:10 ` [PATCH v3 06/21] mm/bootmem_info: Introduce {free,prepare}_vmemmap_page() Muchun Song
2020-11-08 14:10 ` [PATCH v3 07/21] mm/bootmem_info: Combine bootmem info and type into page->freelist Muchun Song
2020-11-08 14:11 ` [PATCH v3 08/21] mm/vmemmap: Initialize page table lock for vmemmap Muchun Song
2020-11-09 18:11 ` Oscar Salvador
2020-11-10 5:17 ` [External] " Muchun Song
2020-11-08 14:11 ` [PATCH v3 09/21] mm/hugetlb: Free the vmemmap pages associated with each hugetlb page Muchun Song
2020-11-09 18:51 ` Oscar Salvador
2020-11-10 6:40 ` [External] " Muchun Song
2020-11-10 9:48 ` Oscar Salvador
2020-11-10 10:47 ` Muchun Song
2020-11-10 13:52 ` Oscar Salvador
2020-11-10 14:00 ` Muchun Song
2020-11-08 14:11 ` [PATCH v3 10/21] mm/hugetlb: Defer freeing of hugetlb pages Muchun Song
2020-11-08 14:11 ` [PATCH v3 11/21] mm/hugetlb: Allocate the vmemmap pages associated with each hugetlb page Muchun Song
2020-11-08 14:11 ` [PATCH v3 12/21] mm/hugetlb: Introduce remap_huge_page_pmd_vmemmap helper Muchun Song
2020-11-08 14:11 ` [PATCH v3 13/21] mm/hugetlb: Use PG_slab to indicate split pmd Muchun Song
2020-11-08 14:11 ` [PATCH v3 14/21] mm/hugetlb: Support freeing vmemmap pages of gigantic page Muchun Song
2020-11-08 14:11 ` [PATCH v3 15/21] mm/hugetlb: Add a BUILD_BUG_ON to check if struct page size is a power of two Muchun Song
2020-11-08 14:11 ` [PATCH v3 16/21] mm/hugetlb: Set the PageHWPoison to the raw error page Muchun Song
2020-11-08 14:11 ` [PATCH v3 17/21] mm/hugetlb: Flush work when dissolving hugetlb page Muchun Song
2020-11-08 14:11 ` [PATCH v3 18/21] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap Muchun Song
2020-11-08 14:11 ` [PATCH v3 19/21] mm/hugetlb: Merge pte to huge pmd only for gigantic page Muchun Song
2020-11-08 14:11 ` [PATCH v3 20/21] mm/hugetlb: Gather discrete indexes of tail page Muchun Song
2020-11-08 14:11 ` [PATCH v3 21/21] mm/hugetlb: Add BUILD_BUG_ON to catch invalid usage of tail struct page Muchun Song
2020-11-10 19:23 ` [PATCH v3 00/21] Free some vmemmap pages of hugetlb page Mike Kravetz
2020-11-11 3:21 ` [External] " Muchun Song
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