On 07/31/2012 03:12 PM, Peter Zijlstra wrote:
+ if (unlikely(pmd_trans_splitting(entry))) {
+ spin_unlock(&mm->page_table_lock);
+ wait_split_huge_page(vma->anon_vma, pmd);
+ return;
+ }
+
+#ifdef CONFIG_NUMA
+ page = pmd_page(entry);
+ VM_BUG_ON(!PageCompound(page) || !PageHead(page));
+
+ get_page(page);
+ spin_unlock(&mm->page_table_lock);
+
+ /*
+ * XXX should we serialize against split_huge_page ?
+ */
I believe we are already serialized here, because we check
for pmd_trans_splitting while holding the page table lock.
The THP code grabs the page table lock when modifying this
status, so we should be good.
+ /*
+ * Due to lacking code to migrate thp pages, we'll split
+ * (which preserves the special PROT_NONE) and re-take the
+ * fault on the normal pages.
+ */
+ split_huge_page(page);
+ put_page(page);
+ return;
Likewise, the THP code serializes split_huge_page, and has
protection against multiple simultaneous invocations of
split_huge_page.
A second invocation of split_huge_page will see that the
page was already split, and it will bail out.
+do_fixup:
+ spin_lock(&mm->page_table_lock);
+ if (unlikely(!pmd_same(*pmd, entry)))
+ goto out_unlock;
If the THP was split for another reason than a NUMA
fault, the !pmd_same check here should result in us
doing the right thing automatically.
I believe this code is correct.
Acked-by: Rik van Riel <r...@redhat.com>
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