From 8952898b0d25223f38daf46b86156fd1c4d17ad0 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Mon, 4 Feb 2008 22:28:45 -0800 Subject: [PATCH] swapin: fix valid_swaphandles defect valid_swaphandles is supposed to do a quick pass over the swap map entries neigbouring the entry which swapin_readahead is targetting, to determine for it a range worth reading all together. But since it always starts its search from the beginning of the swap "cluster", a reject (free entry) there immediately curtails the readaround, and every swapin_readahead from that cluster is for just a single page. Instead scan forwards and backwards around the target entry. Use better names for some variables: a swap_info pointer is usually called "si" not "swapdev". And at the end, if only the target page should be read, return count of 0 to disable readaround, to avoid the unnecessarily repeated call to read_swap_cache_async. Signed-off-by: Hugh Dickins Acked-by: Rik van Riel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/swapfile.c | 49 +++++++++++++++++++++++++++++++++---------------- 1 file changed, 33 insertions(+), 16 deletions(-) diff --git a/mm/swapfile.c b/mm/swapfile.c index ab93505dfbf..f5ba723faf8 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1769,31 +1769,48 @@ get_swap_info_struct(unsigned type) */ int valid_swaphandles(swp_entry_t entry, unsigned long *offset) { + struct swap_info_struct *si; int our_page_cluster = page_cluster; - int ret = 0, i = 1 << our_page_cluster; - unsigned long toff; - struct swap_info_struct *swapdev = swp_type(entry) + swap_info; + pgoff_t target, toff; + pgoff_t base, end; + int nr_pages = 0; if (!our_page_cluster) /* no readahead */ return 0; - toff = (swp_offset(entry) >> our_page_cluster) << our_page_cluster; - if (!toff) /* first page is swap header */ - toff++, i--; - *offset = toff; + + 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); - do { - /* Don't read-ahead past the end of the swap area */ - if (toff >= swapdev->max) + 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 (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 (!swapdev->swap_map[toff]) + if (!si->swap_map[toff]) break; - if (swapdev->swap_map[toff] == SWAP_MAP_BAD) + if (si->swap_map[toff] == SWAP_MAP_BAD) break; - toff++; - ret++; - } while (--i); + } spin_unlock(&swap_lock); - return ret; + + /* + * 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; } -- 2.20.1