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: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index ef14356855d1344d239d2df54f1744e5abd749dd..ce920ca6c90ee43882a23037c067d5cf8ec2f24c 100644 (file)
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -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;
 }