[PATCH v2] mm: use mem_map_offset instead of mem_map_next

Cheng Li
2022-09-05T06:10:06Z

To handle discontiguity 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 mem_map_offset instead of
mem_map_next.

Signed-off-by: Cheng Li <lic121@chinatelecom.cn>
Fixes: 69d177c2fc70 ("hugetlbfs: handle pages higher order than MAX_ORDER")
---

Notes:
v2:
- fix build error

mm/hugetlb.c | 25 +++++++++++++++----------
mm/internal.h | 16 ++--------------
mm/memory.c | 21 ++++++++++-----------
3 files changed, 27 insertions(+), 35 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index e070b8593b37..a9592f69bf82 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1308,12 +1308,13 @@ 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 = mem_map_offset(page, i);
p->mapping = NULL;
clear_compound_head(p);
if (!demote)
@@ -1530,7 +1531,7 @@ 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;
@@ -1561,8 +1562,8 @@ 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 = mem_map_offset(page, i);
subpage->flags &= ~(1 << PG_locked | 1 << PG_error |
1 << PG_referenced | 1 << PG_dirty |
1 << PG_active | 1 << PG_private |
@@ -1769,13 +1770,15 @@ 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 = mem_map_offset(page, i);
+
/*
* For gigantic hugepages allocated through bootmem at
* boot, it's safer to be consistent with the not-gigantic
@@ -1822,14 +1825,16 @@ 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 = mem_map_offset(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 = mem_map_offset(page, j);
__ClearPageReserved(p);
+ }
set_compound_order(page, 0);
#ifdef CONFIG_64BIT
page[1].compound_nr = 0;
diff --git a/mm/internal.h b/mm/internal.h
index 785409805ed7..1012a305a60f 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -646,25 +646,13 @@ static inline void vunmap_range_noflush(unsigned long start, unsigned long end)
*/
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)) {
+ if (unlikely(offset >= MAX_ORDER_NR_PAGES)) {
unsigned long pfn = page_to_pfn(base) + offset;
if (!pfn_valid(pfn))
return NULL;
return pfn_to_page(pfn);
}
- return iter + 1;
+ return base + offset;
}

/* Memory initialisation debug and verification */
diff --git a/mm/memory.c b/mm/memory.c
index 4ba73f5aa8bb..32179c4fd1a5 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5637,11 +5637,11 @@ 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 = mem_map_offset(page, i);
cond_resched();
clear_user_highpage(p, addr + i * PAGE_SIZE);
}
@@ -5677,13 +5677,12 @@ 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 = mem_map_offset(dst_base, i);
+ src = mem_map_offset(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);
}
}

@@ -5730,10 +5729,10 @@ 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 = mem_map_offset(dst_page, i);
if (allow_pagefault)
page_kaddr = kmap(subpage);
else
--
1.8.3.1