From: Lee Schermerhorn This patch simply hooks the anon page fault handler [do_swap_page()] to check for and migrate misplaced pages if enabled and page won't be "COWed". This introduces can_reuse_swap_page() since reuse_swap_page() does delete_from_swap_cache() which messes our migration path (since that assumes its still a swapcache page). Signed-off-by: Lee Schermerhorn [ removed the retry loops after lock_page on a swapcache which tried to fixup the wreckage caused by ignoring the page count on migate; added can_reuse_swap_page(); moved the migrate-on-fault enabled test into check_migrate_misplaced_page() ] Signed-off-by: Peter Zijlstra --- include/linux/swap.h | 4 +++- mm/memory.c | 17 +++++++++++++++++ mm/swapfile.c | 13 +++++++++++++ 3 files changed, 33 insertions(+), 1 deletion(-) --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -342,6 +342,7 @@ extern unsigned int count_swap_pages(int extern sector_t map_swap_page(struct page *, struct block_device **); extern sector_t swapdev_block(int, pgoff_t); extern int reuse_swap_page(struct page *); +extern int can_reuse_swap_page(struct page *); extern int try_to_free_swap(struct page *); struct backing_dev_info; @@ -459,7 +460,8 @@ static inline void delete_from_swap_cach { } -#define reuse_swap_page(page) (page_mapcount(page) == 1) +#define reuse_swap_page(page) (page_mapcount(page) == 1) +#define can_reuse_swap_page(page) (page_mapcount(page) == 1) static inline int try_to_free_swap(struct page *page) { --- a/mm/memory.c +++ b/mm/memory.c @@ -57,6 +57,7 @@ #include #include #include +#include /* check_migrate_misplaced_page() */ #include #include @@ -2962,6 +2963,22 @@ static int do_swap_page(struct mm_struct } /* + * No sense in migrating a page that will be "COWed" as the new + * new page will be allocated according to effective mempolicy. + */ + if ((flags & FAULT_FLAG_WRITE) && can_reuse_swap_page(page)) { + /* + * check for misplacement and migrate, if necessary/possible, + * here and now. Note that if we're racing with another thread, + * we may end up discarding the migrated page after locking + * the page table and checking the pte below. However, we + * don't want to hold the page table locked over migration, so + * we'll live with that [unlikely, one hopes] possibility. + */ + page = check_migrate_misplaced_page(page, vma, address); + } + + /* * Back out if somebody else already faulted in this pte. */ page_table = pte_offset_map_lock(mm, pmd, address, &ptl); --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -640,6 +640,19 @@ int reuse_swap_page(struct page *page) return count <= 1; } +int can_reuse_swap_page(struct page *page) +{ + int count; + + VM_BUG_ON(!PageLocked(page)); + if (unlikely(PageKsm(page))) + return 0; + count = page_mapcount(page); + if (count <= 1 && PageSwapCache(page)) + count += page_swapcount(page); + return count <= 1; +} + /* * If swap is getting full, or if there are no more mappings of this page, * then try_to_free_swap is called to free its swap space. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/