[PATCH 3/4] mm: hugetlb_vmemmap: move PageVmemmapSelfHosted() check to split_vmemmap_huge_pmd()

Muchun Song
2023-11-27T08:47:59Z

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.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
mm/hugetlb_vmemmap.c | 70 +++++++++++++++-----------------------------
1 file changed, 24 insertions(+), 46 deletions(-)

diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index ef14356855d13..ce920ca6c90ee 100644
--- 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;
}

--
2.20.1