On Sat, Jun 11, 2022 at 1:47 AM Miaohe Lin <linmiaohe@xxxxxxxxxx> wrote:
>
> Transhuge swapcaches won't be freed in __collapse_huge_page_copy().
> It's because release_pte_page() is not called for these pages and
> thus free_page_and_swap_cache can't grab the page lock. These pages
> won't be freed from swap cache even if we are the only user until
> next time reclaim. It shouldn't hurt indeed, but we could try to
> free these pages to save more memory for system.
>
> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> ---
> include/linux/swap.h | 5 +++++
> mm/khugepaged.c | 1 +
> mm/swap.h | 5 -----
> 3 files changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 8672a7123ccd..ccb83b12b724 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -456,6 +456,7 @@ static inline unsigned long total_swapcache_pages(void)
> return global_node_page_state(NR_SWAPCACHE);
> }
>
> +extern void free_swap_cache(struct page *page);
> extern void free_page_and_swap_cache(struct page *);
> extern void free_pages_and_swap_cache(struct page **, int);
> /* linux/mm/swapfile.c */
> @@ -540,6 +541,10 @@ static inline void put_swap_device(struct swap_info_struct *si)
> /* used to sanity check ptes in zap_pte_range when CONFIG_SWAP=0 */
> #define free_swap_and_cache(e) is_pfn_swap_entry(e)
>
> +static inline void free_swap_cache(struct page *page)
> +{
> +}
> +
> static inline int add_swap_count_continuation(swp_entry_t swp, gfp_t gfp_mask)
> {
> return 0;
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index ee0a719c8be9..52109ad13f78 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -756,6 +756,7 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
> list_for_each_entry_safe(src_page, tmp, compound_pagelist, lru) {
> list_del(&src_page->lru);
> release_pte_page(src_page);
> + free_swap_cache(src_page);
Will this really work? The free_swap_cache() will just dec refcounts
without putting the page back to buddy. So the hugepage is not
actually freed at all. Am I missing something?
> }
> }
>
> diff --git a/mm/swap.h b/mm/swap.h
> index 0193797b0c92..863f6086c916 100644
> --- a/mm/swap.h
> +++ b/mm/swap.h
> @@ -41,7 +41,6 @@ void __delete_from_swap_cache(struct page *page,
> void delete_from_swap_cache(struct page *page);
> void clear_shadow_from_swap_cache(int type, unsigned long begin,
> unsigned long end);
> -void free_swap_cache(struct page *page);
> struct page *lookup_swap_cache(swp_entry_t entry,
> struct vm_area_struct *vma,
> unsigned long addr);
> @@ -81,10 +80,6 @@ static inline struct address_space *swap_address_space(swp_entry_t entry)
> return NULL;
> }
>
> -static inline void free_swap_cache(struct page *page)
> -{
> -}
> -
> static inline void show_swap_cache_info(void)
> {
> }
> --
> 2.23.0
>
>
