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.
I really don't see how that is currently the case. The buddy deals with
order < MAX_ORDER and we know that these always fall into a single
memory section.
IOW, this patch here would result in overhead where it's not required to
have that overhead.
What am I missing and which scenario are we fixing?
>
> Signed-off-by: Chen Wandun <chenwandun@xxxxxxxxxx>
> ---
> mm/page_alloc.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 855211dea13e..758d8f069b32 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);
> @@ -1199,10 +1199,10 @@ static inline int check_free_page(struct page *page)
> return 1;
> }
>
> -static int free_tail_pages_check(struct page *head_page, struct page *page)
> +static int free_tail_pages_check(struct page *head_page, int index)
> {
> + struct page *page = nth_page(head_page, index);
> int ret = 1;
> -
> /*
> * We rely page->lru.next never has bit 0 set, unless the page
> * is PageTail(). Let's make sure that's true even for poisoned ->lru.
> @@ -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 (index) {
> 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, i);
> + 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))
--
Thanks,
David / dhildenb
