mm: use nth_page instead of mem_map_offset mem_map_next

To handle the discontiguous case, mem_map_next() has a parameter named
`offset`.  As a function caller, one would be confused why "get next
entry" needs a parameter named "offset".  The other drawback of
mem_map_next() is that the callers must take care of the map between
parameter "iter" and "offset", otherwise we may get an hole or duplication
during iteration.  So we use nth_page instead of mem_map_next.

And replace mem_map_offset with nth_page() per Matthew's comments.

Link: https://lkml.kernel.org/r/1662708669-9395-1-git-send-email-lic121@chinatelecom.cn
Signed-off-by: Cheng Li <lic121@chinatelecom.cn>
Fixes: 69d177c2fc70 ("hugetlbfs: handle pages higher order than MAX_ORDER")
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 008955d..6af1233 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1306,12 +1306,13 @@ static void __destroy_compound_gigantic_page(struct page *page,
 {
        int i;
        int nr_pages = 1 << order;
-       struct page *p = page + 1;
+       struct page *p;
 
        atomic_set(compound_mapcount_ptr(page), 0);
        atomic_set(compound_pincount_ptr(page), 0);
 
-       for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
+       for (i = 1; i < nr_pages; i++) {
+               p = nth_page(page, i);
                p->mapping = NULL;
                clear_compound_head(p);
                if (!demote)
@@ -1532,7 +1533,7 @@ static void add_hugetlb_page(struct hstate *h, struct page *page,
 static void __update_and_free_page(struct hstate *h, struct page *page)
 {
        int i;
-       struct page *subpage = page;
+       struct page *subpage;
 
        if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
                return;
@@ -1563,8 +1564,8 @@ static void __update_and_free_page(struct hstate *h, struct page *page)
        if (unlikely(PageHWPoison(page)))
                hugetlb_clear_page_hwpoison(page);
 
-       for (i = 0; i < pages_per_huge_page(h);
-            i++, subpage = mem_map_next(subpage, page, i)) {
+       for (i = 0; i < pages_per_huge_page(h); i++) {
+               subpage = nth_page(page, i);
                subpage->flags &= ~(1 << PG_locked | 1 << PG_error |
                                1 << PG_referenced | 1 << PG_dirty |
                                1 << PG_active | 1 << PG_private |
@@ -1771,13 +1772,15 @@ static bool __prep_compound_gigantic_page(struct page *page, unsigned int order,
 {
        int i, j;
        int nr_pages = 1 << order;
-       struct page *p = page + 1;
+       struct page *p;
 
        /* we rely on prep_new_huge_page to set the destructor */
        set_compound_order(page, order);
        __ClearPageReserved(page);
        __SetPageHead(page);
-       for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
+       for (i = 1; i < nr_pages; i++) {
+               p = nth_page(page, i);
+
                /*
                 * For gigantic hugepages allocated through bootmem at
                 * boot, it's safer to be consistent with the not-gigantic
@@ -1824,14 +1827,16 @@ static bool __prep_compound_gigantic_page(struct page *page, unsigned int order,
 
 out_error:
        /* undo tail page modifications made above */
-       p = page + 1;
-       for (j = 1; j < i; j++, p = mem_map_next(p, page, j)) {
+       for (j = 1; j < i; j++) {
+               p = nth_page(page, j);
                clear_compound_head(p);
                set_page_refcounted(p);
        }
        /* need to clear PG_reserved on remaining tail pages  */
-       for (; j < nr_pages; j++, p = mem_map_next(p, page, j))
+       for (; j < nr_pages; j++) {
+               p = nth_page(page, j);
                __ClearPageReserved(p);
+       }
        set_compound_order(page, 0);
 #ifdef CONFIG_64BIT
        page[1].compound_nr = 0;
@@ -6128,7 +6133,7 @@ static void record_subpages_vmas(struct page *page, struct vm_area_struct *vma,
 
        for (nr = 0; nr < refs; nr++) {
                if (likely(pages))
-                       pages[nr] = mem_map_offset(page, nr);
+                       pages[nr] = nth_page(page, nr);
                if (vmas)
                        vmas[nr] = vma;
        }
@@ -6292,7 +6297,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
                    (vma->vm_end - ALIGN_DOWN(vaddr, PAGE_SIZE)) >> PAGE_SHIFT);
 
                if (pages || vmas)
-                       record_subpages_vmas(mem_map_offset(page, pfn_offset),
+                       record_subpages_vmas(nth_page(page, pfn_offset),
                                             vma, refs,
                                             likely(pages) ? pages + i : NULL,
                                             vmas ? vmas + i : NULL);

diff --git a/mm/internal.h b/mm/internal.h
index 0f106a3..e497ab1 100644 (file)
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -638,34 +638,6 @@ static inline void vunmap_range_noflush(unsigned long start, unsigned long end)
 }
 #endif /* !CONFIG_MMU */
 
-/*
- * Return the mem_map entry representing the 'offset' subpage within
- * the maximally aligned gigantic page 'base'.  Handle any discontiguity
- * in the mem_map at MAX_ORDER_NR_PAGES boundaries.
- */
-static inline struct page *mem_map_offset(struct page *base, int offset)
-{
-       if (unlikely(offset >= MAX_ORDER_NR_PAGES))
-               return nth_page(base, offset);
-       return base + offset;
-}
-
-/*
- * Iterator over all subpages within the maximally aligned gigantic
- * page 'base'.  Handle any discontiguity in the mem_map.
- */
-static inline struct page *mem_map_next(struct page *iter,
-                                               struct page *base, int offset)
-{
-       if (unlikely((offset & (MAX_ORDER_NR_PAGES - 1)) == 0)) {
-               unsigned long pfn = page_to_pfn(base) + offset;
-               if (!pfn_valid(pfn))
-                       return NULL;
-               return pfn_to_page(pfn);
-       }
-       return iter + 1;
-}
-
 /* Memory initialisation debug and verification */
 enum mminit_level {
        MMINIT_WARNING,

diff --git a/mm/memory.c b/mm/memory.c
index d671ad3..c01c125 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5690,11 +5690,11 @@ static void clear_gigantic_page(struct page *page,
                                unsigned int pages_per_huge_page)
 {
        int i;
-       struct page *p = page;
+       struct page *p;
 
        might_sleep();
-       for (i = 0; i < pages_per_huge_page;
-            i++, p = mem_map_next(p, page, i)) {
+       for (i = 0; i < pages_per_huge_page; i++) {
+               p = nth_page(page, i);
                cond_resched();
                clear_user_highpage(p, addr + i * PAGE_SIZE);
        }
@@ -5730,13 +5730,12 @@ static void copy_user_gigantic_page(struct page *dst, struct page *src,
        struct page *dst_base = dst;
        struct page *src_base = src;
 
-       for (i = 0; i < pages_per_huge_page; ) {
+       for (i = 0; i < pages_per_huge_page; i++) {
+               dst = nth_page(dst_base, i);
+               src = nth_page(src_base, i);
+
                cond_resched();
                copy_user_highpage(dst, src, addr + i*PAGE_SIZE, vma);
-
-               i++;
-               dst = mem_map_next(dst, dst_base, i);
-               src = mem_map_next(src, src_base, i);
        }
 }
 
@@ -5783,10 +5782,10 @@ long copy_huge_page_from_user(struct page *dst_page,
        void *page_kaddr;
        unsigned long i, rc = 0;
        unsigned long ret_val = pages_per_huge_page * PAGE_SIZE;
-       struct page *subpage = dst_page;
+       struct page *subpage;
 
-       for (i = 0; i < pages_per_huge_page;
-            i++, subpage = mem_map_next(subpage, dst_page, i)) {
+       for (i = 0; i < pages_per_huge_page; i++) {
+               subpage = nth_page(dst_page, i);
                if (allow_pagefault)
                        page_kaddr = kmap(subpage);
                else