Re: [PATCH 2/2] mm: fix contiguous memmap assumptions about alloc/free pages

Re: [PATCH 2/2] mm: fix contiguous memmap assumptions about alloc/free pages

[Matthew Wilcox]

On Tue, Mar 29, 2022 at 09:09:28PM +0800, Chen Wandun wrote:
> +#define page_nth(head, tail)	(page_to_pfn(tail) - page_to_pfn(head))

Could we avoid reintroducing page_nth()?  It is a terrible name.

> @@ -1213,7 +1213,7 @@ static int free_tail_pages_check(struct page *head_page, struct page *page)
>  		ret = 0;
>  		goto out;
>  	}
> -	switch (page - head_page) {
> +	switch (page_nth(head_page, page)) {
>  	case 1:
>  		/* the first tail page: ->mapping may be compound_mapcount() */
>  		if (unlikely(compound_mapcount(page))) {

This is the only place you use it.  I'd suggest free_tail_pages_check()
should take 'i' as its second parameter instead of 'page + i', then
there's no need to convert back to i.

[PATCH 0/2] fix several contiguous memmap assumptions

[Chen Wandun]

It isn't true for only SPARSEMEM configs to assume that a compound page
has virtually contiguous page structs, so use nth_page to iterate each
page.

Inspired by:
https://lore.kernel.org/linux-mm/20220204195852.1751729-8-willy@infradead.org/

Chen Wandun (2):
  mm: fix contiguous memmap assumptions about split page
  mm: fix contiguous memmap assumptions about alloc/free pages

 include/linux/mm.h |  2 ++
 mm/compaction.c    |  6 +++---
 mm/huge_memory.c   |  2 +-
 mm/page_alloc.c    | 14 ++++++++------
 4 files changed, 14 insertions(+), 10 deletions(-)

-- 
2.18.0.huawei.25

[PATCH 1/2] mm: fix contiguous memmap assumptions about split page

[Chen Wandun]

It isn't true for only SPARSEMEM configs to assume that a compound page
has virtually contiguous page structs, so use nth_page to iterate each
page.

Inspired by:
https://lore.kernel.org/linux-mm/20220204195852.1751729-8-willy@infradead.org/

Signed-off-by: Chen Wandun <chenwandun@huawei.com>
---
 mm/compaction.c  | 6 +++---
 mm/huge_memory.c | 2 +-
 mm/page_alloc.c  | 2 +-
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index c3e37aa9ff9e..ddff13b968a2 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -87,7 +87,7 @@ static unsigned long release_freepages(struct list_head *freelist)
 static void split_map_pages(struct list_head *list)
 {
 	unsigned int i, order, nr_pages;
-	struct page *page, *next;
+	struct page *page, *next, *tmp;
 	LIST_HEAD(tmp_list);
 
 	list_for_each_entry_safe(page, next, list, lru) {
@@ -101,8 +101,8 @@ static void split_map_pages(struct list_head *list)
 			split_page(page, order);
 
 		for (i = 0; i < nr_pages; i++) {
-			list_add(&page->lru, &tmp_list);
-			page++;
+			tmp = nth_page(page, i);
+			list_add(&tmp->lru, &tmp_list);
 		}
 	}
 
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 2fe38212e07c..d77fc2ad581d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2297,7 +2297,7 @@ static void lru_add_page_tail(struct page *head, struct page *tail,
 static void __split_huge_page_tail(struct page *head, int tail,
 		struct lruvec *lruvec, struct list_head *list)
 {
-	struct page *page_tail = head + tail;
+	struct page *page_tail = nth_page(head, tail);
 
 	VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail);
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f648decfe39d..855211dea13e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3513,7 +3513,7 @@ void split_page(struct page *page, unsigned int order)
 	VM_BUG_ON_PAGE(!page_count(page), page);
 
 	for (i = 1; i < (1 << order); i++)
-		set_page_refcounted(page + i);
+		set_page_refcounted(nth_page(page, i));
 	split_page_owner(page, 1 << order);
 	split_page_memcg(page, 1 << order);
 }
-- 
2.18.0.huawei.25

[PATCH 2/2] mm: fix contiguous memmap assumptions about alloc/free pages

[Chen Wandun]

It isn't true for only SPARSEMEM configs to assume that a compound page
has virtually contiguous page structs, so use nth_page to iterate each
page.

Signed-off-by: Chen Wandun <chenwandun@huawei.com>
---
 include/linux/mm.h |  2 ++
 mm/page_alloc.c    | 12 +++++++-----
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 355075fb2654..ef48cfef7c67 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -212,9 +212,11 @@ int overcommit_policy_handler(struct ctl_table *, int, void *, size_t *,
 
 #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
 #define nth_page(page,n) pfn_to_page(page_to_pfn((page)) + (n))
+#define page_nth(head, tail)	(page_to_pfn(tail) - page_to_pfn(head))
 #define folio_page_idx(folio, p)	(page_to_pfn(p) - folio_pfn(folio))
 #else
 #define nth_page(page,n) ((page) + (n))
+#define page_nth(head, tail)	((tail) - (head))
 #define folio_page_idx(folio, p)	((p) - &(folio)->page)
 #endif
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 855211dea13e..09bc63992d20 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -721,7 +721,7 @@ static void prep_compound_head(struct page *page, unsigned int order)
 
 static void prep_compound_tail(struct page *head, int tail_idx)
 {
-	struct page *p = head + tail_idx;
+	struct page *p = nth_page(head, tail_idx);
 
 	p->mapping = TAIL_MAPPING;
 	set_compound_head(p, head);
@@ -1213,7 +1213,7 @@ static int free_tail_pages_check(struct page *head_page, struct page *page)
 		ret = 0;
 		goto out;
 	}
-	switch (page - head_page) {
+	switch (page_nth(head_page, page)) {
 	case 1:
 		/* the first tail page: ->mapping may be compound_mapcount() */
 		if (unlikely(compound_mapcount(page))) {
@@ -1322,6 +1322,7 @@ static __always_inline bool free_pages_prepare(struct page *page,
 	if (unlikely(order)) {
 		bool compound = PageCompound(page);
 		int i;
+		struct page *tail_page;
 
 		VM_BUG_ON_PAGE(compound && compound_order(page) != order, page);
 
@@ -1330,13 +1331,14 @@ static __always_inline bool free_pages_prepare(struct page *page,
 			ClearPageHasHWPoisoned(page);
 		}
 		for (i = 1; i < (1 << order); i++) {
+			tail_page = nth_page(page, i);
 			if (compound)
-				bad += free_tail_pages_check(page, page + i);
-			if (unlikely(check_free_page(page + i))) {
+				bad += free_tail_pages_check(page, tail_page);
+			if (unlikely(check_free_page(tail_page))) {
 				bad++;
 				continue;
 			}
-			(page + i)->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
+			tail_page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
 		}
 	}
 	if (PageMappingFlags(page))
-- 
2.18.0.huawei.25

Re: [PATCH 2/2] mm: fix contiguous memmap assumptions about alloc/free pages

[Chen Wandun]

on 2022/3/29 21:08, Matthew Wilcox wrote:
> On Tue, Mar 29, 2022 at 09:09:28PM +0800, Chen Wandun wrote:
>> +#define page_nth(head, tail)	(page_to_pfn(tail) - page_to_pfn(head))
> Could we avoid reintroducing page_nth()?  It is a terrible name.
how about compound_index ?
>> @@ -1213,7 +1213,7 @@ static int free_tail_pages_check(struct page *head_page, struct page *page)
>>   		ret = 0;
>>   		goto out;
>>   	}
>> -	switch (page - head_page) {
>> +	switch (page_nth(head_page, page)) {
>>   	case 1:
>>   		/* the first tail page: ->mapping may be compound_mapcount() */
>>   		if (unlikely(compound_mapcount(page))) {
> This is the only place you use it.  I'd suggest free_tail_pages_check()
> should take 'i' as its second parameter instead of 'page + i', then
> there's no need to convert back to i.
OK， I will send v2， but I'm not sure whether similar function like 
page_nth is needed elsewhere

>
> .