patches/old/hugetlb-fix-comments-about-avoiding-atomic-allocation-of-vmemmap-pages.patch

From: luofei <luofei@unicloud.com>
Subject: hugetlb: fix comments about avoiding atomic allocation of vmemmap pages

Since there is no longer an atomic allocation of vmemmap pages, but a
fixed flag(GFP_KERNEL | __GFP_NORETRY | __GFP_THISNODE) is used.  The
description of atomicity here is some what inappropriate.

And the atomic parameter naming of update_and_free_page() may be
misleading, add a comment here.

Link: https://lkml.kernel.org/r/20220316031602.377452-1-luofei@unicloud.com
Signed-off-by: luofei <luofei@unicloud.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/hugetlb.c |   17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

--- a/mm/hugetlb.c~hugetlb-fix-comments-about-avoiding-atomic-allocation-of-vmemmap-pages
+++ a/mm/hugetlb.c
@@ -1567,10 +1567,12 @@ static void __update_and_free_page(struc
 }
 
 /*
- * As update_and_free_page() can be called under any context, so we cannot
- * use GFP_KERNEL to allocate vmemmap pages. However, we can defer the
- * actual freeing in a workqueue to prevent from using GFP_ATOMIC to allocate
- * the vmemmap pages.
+ * Freeing hugetlb pages in done in update_and_free_page(). When freeing
+ * a hugetlb page, vmemmap pages may need to be allocated. The routine
+ * alloc_huge_page_vmemmap() can possibly sleep as it uses GFP_KERNEL.
+ * However, update_and_free_page() can be called under any context. To
+ * avoid the possibility of sleeping in a context where sleeping is not
+ * allowed, defer the actual freeing in a workqueue where sleeping is allowed.
  *
  * free_hpage_workfn() locklessly retrieves the linked list of pages to be
  * freed and frees them one-by-one. As the page->mapping pointer is going
@@ -1614,6 +1616,10 @@ static inline void flush_free_hpage_work
 		flush_work(&free_hpage_work);
 }
 
+/*
+ * atomic == true indicates called from a context where sleeping is
+ * not allowed.
+ */
 static void update_and_free_page(struct hstate *h, struct page *page,
 				 bool atomic)
 {
@@ -1623,7 +1629,8 @@ static void update_and_free_page(struct
 	}
 
 	/*
-	 * Defer freeing to avoid using GFP_ATOMIC to allocate vmemmap pages.
+	 * Defer freeing to avoid possible sleeping when allocating
+	 * vmemmap pages.
 	 *
 	 * Only call schedule_work() if hpage_freelist is previously
 	 * empty. Otherwise, schedule_work() had been called but the workfn
_