From e8c26ab60598558ec3a626e7925b06e7417d7710 Mon Sep 17 00:00:00 2001 From: Tim Chen Date: Wed, 22 Feb 2017 15:45:29 -0800 Subject: [PATCH] mm/swap: skip readahead for unreferenced swap slots We can avoid needlessly allocating page for swap slots that are not used by anyone. No pages have to be read in for these slots. Link: http://lkml.kernel.org/r/0784b3f20b9bd3aa5552219624cb78dc4ae710c9.1484082593.git.tim.c.chen@linux.intel.com Signed-off-by: Tim Chen Signed-off-by: "Huang, Ying" Cc: Aaron Lu Cc: Andi Kleen Cc: Andrea Arcangeli Cc: Christian Borntraeger Cc: Dave Hansen Cc: Hillf Danton Cc: Huang Ying Cc: Hugh Dickins Cc: Johannes Weiner Cc: Jonathan Corbet escreveu: Cc: Kirill A. Shutemov Cc: Michal Hocko Cc: Minchan Kim Cc: Rik van Riel Cc: Shaohua Li Cc: Vladimir Davydov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/swap.h | 6 ++++++ mm/swap_state.c | 4 ++++ mm/swapfile.c | 47 ++++++++++++++++++++++++++++++++++++++------ 3 files changed, 51 insertions(+), 6 deletions(-) diff --git a/include/linux/swap.h b/include/linux/swap.h index 648a32b58e3e..3116382067cd 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -398,6 +398,7 @@ extern unsigned int count_swap_pages(int, int); extern sector_t map_swap_page(struct page *, struct block_device **); extern sector_t swapdev_block(int, pgoff_t); extern int page_swapcount(struct page *); +extern int __swp_swapcount(swp_entry_t entry); extern int swp_swapcount(swp_entry_t entry); extern struct swap_info_struct *page_swap_info(struct page *); extern bool reuse_swap_page(struct page *, int *); @@ -492,6 +493,11 @@ static inline int page_swapcount(struct page *page) return 0; } +static inline int __swp_swapcount(swp_entry_t entry) +{ + return 0; +} + static inline int swp_swapcount(swp_entry_t entry) { return 0; diff --git a/mm/swap_state.c b/mm/swap_state.c index 3863acd6189c..3d76d80c07d6 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -323,6 +323,10 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, if (found_page) break; + /* Just skip read ahead for unused swap slot */ + if (!__swp_swapcount(entry)) + return NULL; + /* * Get a new page to read into from swap. */ diff --git a/mm/swapfile.c b/mm/swapfile.c index 66e95eb73040..7e888de35c41 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -798,7 +798,7 @@ swp_entry_t get_swap_page_of_type(int type) return (swp_entry_t) {0}; } -static struct swap_info_struct *_swap_info_get(swp_entry_t entry) +static struct swap_info_struct *__swap_info_get(swp_entry_t entry) { struct swap_info_struct *p; unsigned long offset, type; @@ -814,13 +814,8 @@ static struct swap_info_struct *_swap_info_get(swp_entry_t entry) offset = swp_offset(entry); if (offset >= p->max) goto bad_offset; - if (!p->swap_map[offset]) - goto bad_free; return p; -bad_free: - pr_err("swap_info_get: %s%08lx\n", Unused_offset, entry.val); - goto out; bad_offset: pr_err("swap_info_get: %s%08lx\n", Bad_offset, entry.val); goto out; @@ -833,6 +828,24 @@ out: return NULL; } +static struct swap_info_struct *_swap_info_get(swp_entry_t entry) +{ + struct swap_info_struct *p; + + p = __swap_info_get(entry); + if (!p) + goto out; + if (!p->swap_map[swp_offset(entry)]) + goto bad_free; + return p; + +bad_free: + pr_err("swap_info_get: %s%08lx\n", Unused_offset, entry.val); + goto out; +out: + return NULL; +} + static struct swap_info_struct *swap_info_get(swp_entry_t entry) { struct swap_info_struct *p; @@ -986,6 +999,28 @@ int page_swapcount(struct page *page) return count; } +/* + * How many references to @entry are currently swapped out? + * This does not give an exact answer when swap count is continued, + * but does include the high COUNT_CONTINUED flag to allow for that. + */ +int __swp_swapcount(swp_entry_t entry) +{ + int count = 0; + pgoff_t offset; + struct swap_info_struct *si; + struct swap_cluster_info *ci; + + si = __swap_info_get(entry); + if (si) { + offset = swp_offset(entry); + ci = lock_cluster_or_swap_info(si, offset); + count = swap_count(si->swap_map[offset]); + unlock_cluster_or_swap_info(si, ci); + } + return count; +} + /* * How many references to @entry are currently swapped out? * This considers COUNT_CONTINUED so it returns exact answer. -- 2.20.1