From 4b3ef9daa4fc0bba742a79faecb17fdaaead083b Mon Sep 17 00:00:00 2001 From: "Huang, Ying" Date: Wed, 22 Feb 2017 15:45:26 -0800 Subject: mm/swap: split swap cache into 64MB trunks The patch is to improve the scalability of the swap out/in via using fine grained locks for the swap cache. In current kernel, one address space will be used for each swap device. And in the common configuration, the number of the swap device is very small (one is typical). This causes the heavy lock contention on the radix tree of the address space if multiple tasks swap out/in concurrently. But in fact, there is no dependency between pages in the swap cache. So that, we can split the one shared address space for each swap device into several address spaces to reduce the lock contention. In the patch, the shared address space is split into 64MB trunks. 64MB is chosen to balance the memory space usage and effect of lock contention reduction. The size of struct address_space on x86_64 architecture is 408B, so with the patch, 6528B more memory will be used for every 1GB swap space on x86_64 architecture. One address space is still shared for the swap entries in the same 64M trunks. To avoid lock contention for the first round of swap space allocation, the order of the swap clusters in the initial free clusters list is changed. The swap space distance between the consecutive swap clusters in the free cluster list is at least 64M. After the first round of allocation, the swap clusters are expected to be freed randomly, so the lock contention should be reduced effectively. Link: http://lkml.kernel.org/r/735bab895e64c930581ffb0a05b661e01da82bc5.1484082593.git.tim.c.chen@linux.intel.com Signed-off-by: "Huang, Ying" Signed-off-by: Tim Chen 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 --- mm/swapfile.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) (limited to 'mm/swapfile.c') diff --git a/mm/swapfile.c b/mm/swapfile.c index eb71b5d9430b..66e95eb73040 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -2084,6 +2084,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) vfree(frontswap_map); /* Destroy swap account information */ swap_cgroup_swapoff(p->type); + exit_swap_address_space(p->type); inode = mapping->host; if (S_ISBLK(inode->i_mode)) { @@ -2407,8 +2408,12 @@ static unsigned long read_swap_header(struct swap_info_struct *p, return maxpages; } -#define SWAP_CLUSTER_COLS \ +#define SWAP_CLUSTER_INFO_COLS \ DIV_ROUND_UP(L1_CACHE_BYTES, sizeof(struct swap_cluster_info)) +#define SWAP_CLUSTER_SPACE_COLS \ + DIV_ROUND_UP(SWAP_ADDRESS_SPACE_PAGES, SWAPFILE_CLUSTER) +#define SWAP_CLUSTER_COLS \ + max_t(unsigned int, SWAP_CLUSTER_INFO_COLS, SWAP_CLUSTER_SPACE_COLS) static int setup_swap_map_and_extents(struct swap_info_struct *p, union swap_header *swap_header, @@ -2471,7 +2476,10 @@ static int setup_swap_map_and_extents(struct swap_info_struct *p, return nr_extents; - /* Reduce false cache line sharing between cluster_info */ + /* + * Reduce false cache line sharing between cluster_info and + * sharing same address space. + */ for (k = 0; k < SWAP_CLUSTER_COLS; k++) { j = (k + col) % SWAP_CLUSTER_COLS; for (i = 0; i < DIV_ROUND_UP(nr_clusters, SWAP_CLUSTER_COLS); i++) { @@ -2661,6 +2669,10 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) } } + error = init_swap_address_space(p->type, maxpages); + if (error) + goto bad_swap; + mutex_lock(&swapon_mutex); prio = -1; if (swap_flags & SWAP_FLAG_PREFER) -- cgit v1.2.3