2022-03-30 17:47:32

by Chen Wandun

Subject: [PATCH v2 1/2] mm: fix contiguous memmap assumptions about split page

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/[email protected]/

Signed-off-by: Chen Wandun <[email protected]>
---
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

2022-03-31 03:30:06

by David Hildenbrand

Subject: Re: [PATCH v2 1/2] mm: fix contiguous memmap assumptions about split page

On 30.03.22 12:25, Chen Wandun wrote:
> 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.

Is this actually a "fix" or rather a preparation for having very large
compound pages (>= MAX_ORDER) that we'd be able to split?

Naive me would think that we'd currently only have order < MAX_ORDER,
and consequently would always fall into a single memory section where
the memmap is contiguous.

>
> Inspired by:
> https://lore.kernel.org/linux-mm/[email protected]/
>
> Signed-off-by: Chen Wandun <[email protected]>
> ---
> 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);
> }


--
Thanks,

David / dhildenb