On 2022/6/16 1:13, Zach O'Keefe wrote: > On 11 Jun 16:47, Miaohe Lin 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); >> } >> } > > Aside: in __collapse_huge_page_isolate() (and also here) why can't we just check > PageCompound(page) && page == compound_head(page) to only act on compound pages > once? AFAIK this would alleviate this compound_pagelist business.. > > Anyways, as-is, free_page_and_swap_cache() won't be able to do > try_to_free_swap(), since it can't grab page lock, put it will call put_page(). > I think (?) the last page ref might be dropped in release_pte_page(), so should > free_swap_cache() come before it? Thanks for catching this! If page is not in swapcache, the last page ref might be dropped. So it's bad to call free_swap_cache() after it. Thanks! > >> >> 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 >> >> > . >