From 67f96aa252e606cdf6c3cf1032952ec207ec0cf0 Mon Sep 17 00:00:00 2001 From: Rik van Riel Date: Wed, 21 Mar 2012 16:33:50 -0700 Subject: [PATCH] mm: make swapin readahead skip over holes Ever since abandoning the virtual scan of processes, for scalability reasons, swap space has been a little more fragmented than before. This can lead to the situation where a large memory user is killed, swap space ends up full of "holes" and swapin readahead is totally ineffective. On my home system, after killing a leaky firefox it took over an hour to page just under 2GB of memory back in, slowing the virtual machines down to a crawl. This patch makes swapin readahead simply skip over holes, instead of stopping at them. This allows the system to swap things back in at rates of several MB/second, instead of a few hundred kB/second. The checks done in valid_swaphandles are already done in read_swap_cache_async as well, allowing us to remove a fair amount of code. [akpm@linux-foundation.org: fix it for page_cluster >= 32] Signed-off-by: Rik van Riel Cc: Minchan Kim Cc: KOSAKI Motohiro Acked-by: Johannes Weiner Acked-by: Mel Gorman Cc: Adrian Drzewiecki Cc: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/swap.h | 1 - mm/swap_state.c | 24 ++++++++++---------- mm/swapfile.c | 52 -------------------------------------------- 3 files changed, 11 insertions(+), 66 deletions(-) diff --git a/include/linux/swap.h b/include/linux/swap.h index 3e60228e7299..64a7dba67840 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -329,7 +329,6 @@ extern long total_swap_pages; extern void si_swapinfo(struct sysinfo *); extern swp_entry_t get_swap_page(void); extern swp_entry_t get_swap_page_of_type(int); -extern int valid_swaphandles(swp_entry_t, unsigned long *); extern int add_swap_count_continuation(swp_entry_t, gfp_t); extern void swap_shmem_alloc(swp_entry_t); extern int swap_duplicate(swp_entry_t); diff --git a/mm/swap_state.c b/mm/swap_state.c index ea6b32d61873..9d3dd3763cf7 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -372,25 +372,23 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask, struct vm_area_struct *vma, unsigned long addr) { - int nr_pages; struct page *page; - unsigned long offset; - unsigned long end_offset; + unsigned long offset = swp_offset(entry); + unsigned long start_offset, end_offset; + unsigned long mask = (1UL << page_cluster) - 1; - /* - * Get starting offset for readaround, and number of pages to read. - * Adjust starting address by readbehind (for NUMA interleave case)? - * No, it's very unlikely that swap layout would follow vma layout, - * more likely that neighbouring swap pages came from the same node: - * so use the same "addr" to choose the same node for each swap read. - */ - nr_pages = valid_swaphandles(entry, &offset); - for (end_offset = offset + nr_pages; offset < end_offset; offset++) { + /* Read a page_cluster sized and aligned cluster around offset. */ + start_offset = offset & ~mask; + end_offset = offset | mask; + if (!start_offset) /* First page is swap header. */ + start_offset++; + + for (offset = start_offset; offset <= end_offset ; offset++) { /* Ok, do the async read-ahead now */ page = read_swap_cache_async(swp_entry(swp_type(entry), offset), gfp_mask, vma, addr); if (!page) - break; + continue; page_cache_release(page); } lru_add_drain(); /* Push any new pages onto the LRU now */ diff --git a/mm/swapfile.c b/mm/swapfile.c index 44595a373e42..b82c028cfcc6 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -2287,58 +2287,6 @@ int swapcache_prepare(swp_entry_t entry) return __swap_duplicate(entry, SWAP_HAS_CACHE); } -/* - * swap_lock prevents swap_map being freed. Don't grab an extra - * reference on the swaphandle, it doesn't matter if it becomes unused. - */ -int valid_swaphandles(swp_entry_t entry, unsigned long *offset) -{ - struct swap_info_struct *si; - int our_page_cluster = page_cluster; - pgoff_t target, toff; - pgoff_t base, end; - int nr_pages = 0; - - if (!our_page_cluster) /* no readahead */ - return 0; - - si = swap_info[swp_type(entry)]; - target = swp_offset(entry); - base = (target >> our_page_cluster) << our_page_cluster; - end = base + (1 << our_page_cluster); - if (!base) /* first page is swap header */ - base++; - - spin_lock(&swap_lock); - if (end > si->max) /* don't go beyond end of map */ - end = si->max; - - /* Count contiguous allocated slots above our target */ - for (toff = target; ++toff < end; nr_pages++) { - /* Don't read in free or bad pages */ - if (!si->swap_map[toff]) - break; - if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD) - break; - } - /* Count contiguous allocated slots below our target */ - for (toff = target; --toff >= base; nr_pages++) { - /* Don't read in free or bad pages */ - if (!si->swap_map[toff]) - break; - if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD) - break; - } - spin_unlock(&swap_lock); - - /* - * Indicate starting offset, and return number of pages to get: - * if only 1, say 0, since there's then no readahead to be done. - */ - *offset = ++toff; - return nr_pages? ++nr_pages: 0; -} - /* * add_swap_count_continuation - called when a swap count is duplicated * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's -- GitLab