Commit be035a2a authored by Muchun Song's avatar Muchun Song Committed by Andrew Morton
Browse files

mm: hugetlb_vmemmap: move PageVmemmapSelfHosted() check to split_vmemmap_huge_pmd() 

To check a page whether it is self-hosted needs to traverse the page table
(e.g.  pmd_off_k()), however, we already have done this in the next
calling of vmemmap_remap_range().  Moving PageVmemmapSelfHosted() check to
vmemmap_pmd_entry() could simplify the code a bit.

Link: https://lkml.kernel.org/r/20231127084645.27017-4-songmuchun@bytedance.com


Signed-off-by: default avatarMuchun Song <songmuchun@bytedance.com>
Reviewed-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent fb93ed63

mm/hugetlb_vmemmap.c

+24 −46
Original line number Diff line number Diff line
@@ -95,6 +95,7 @@ static int vmemmap_split_pmd(pmd_t *pmd, struct page *head, unsigned long start, 
static int vmemmap_pmd_entry(pmd_t *pmd, unsigned long addr,

			     unsigned long next, struct mm_walk *walk)

{

	int ret = 0;

	struct page *head;

	struct vmemmap_remap_walk *vmemmap_walk = walk->private;
@@ -104,9 +105,30 @@ static int vmemmap_pmd_entry(pmd_t *pmd, unsigned long addr, 


	spin_lock(&init_mm.page_table_lock);

	head = pmd_leaf(*pmd) ? pmd_page(*pmd) : NULL;

	/*

	 * Due to HugeTLB alignment requirements and the vmemmap

	 * pages being at the start of the hotplugged memory

	 * region in memory_hotplug.memmap_on_memory case. Checking

	 * the vmemmap page associated with the first vmemmap page

	 * if it is self-hosted is sufficient.

	 *

	 * [                  hotplugged memory                  ]

	 * [        section        ][...][        section        ]

	 * [ vmemmap ][              usable memory               ]

	 *   ^  | ^                        |

	 *   +--+ |                        |

	 *        +------------------------+

	 */

	if (unlikely(!vmemmap_walk->nr_walked)) {

		struct page *page = head ? head + pte_index(addr) :

				    pte_page(ptep_get(pte_offset_kernel(pmd, addr)));



		if (PageVmemmapSelfHosted(page))

			ret = -ENOTSUPP;

	}

	spin_unlock(&init_mm.page_table_lock);

	if (!head)

		return 0;

	if (!head || ret)

		return ret;



	return vmemmap_split_pmd(pmd, head, addr & PMD_MASK, vmemmap_walk);

}
@@ -524,50 +546,6 @@ static bool vmemmap_should_optimize(const struct hstate *h, const struct page *h 
	if (!hugetlb_vmemmap_optimizable(h))

		return false;



	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) {

		pmd_t *pmdp, pmd;

		struct page *vmemmap_page;

		unsigned long vaddr = (unsigned long)head;



		/*

		 * Only the vmemmap page's vmemmap page can be self-hosted.

		 * Walking the page tables to find the backing page of the

		 * vmemmap page.

		 */

		pmdp = pmd_off_k(vaddr);

		/*

		 * The READ_ONCE() is used to stabilize *pmdp in a register or

		 * on the stack so that it will stop changing under the code.

		 * The only concurrent operation where it can be changed is

		 * split_vmemmap_huge_pmd() (*pmdp will be stable after this

		 * operation).

		 */

		pmd = READ_ONCE(*pmdp);

		if (pmd_leaf(pmd))

			vmemmap_page = pmd_page(pmd) + pte_index(vaddr);

		else

			vmemmap_page = pte_page(*pte_offset_kernel(pmdp, vaddr));

		/*

		 * Due to HugeTLB alignment requirements and the vmemmap pages

		 * being at the start of the hotplugged memory region in

		 * memory_hotplug.memmap_on_memory case. Checking any vmemmap

		 * page's vmemmap page if it is marked as VmemmapSelfHosted is

		 * sufficient.

		 *

		 * [                  hotplugged memory                  ]

		 * [        section        ][...][        section        ]

		 * [ vmemmap ][              usable memory               ]

		 *   ^   |     |                                        |

		 *   +---+     |                                        |

		 *     ^       |                                        |

		 *     +-------+                                        |

		 *          ^                                           |

		 *          +-------------------------------------------+

		 */

		if (PageVmemmapSelfHosted(vmemmap_page))

			return false;

	}



	return true;

}