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authorHuang, Ying <ying.huang@intel.com>2017-02-22 15:45:26 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2017-02-22 16:41:30 -0800
commit4b3ef9daa4fc0bba742a79faecb17fdaaead083b (patch)
tree52a387923455792179754189a685ba9c01f4b160 /mm/swap_state.c
parent235b62176712b970c815923e36b9a9cc05d4d901 (diff)
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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" <ying.huang@intel.com> Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com> Cc: Aaron Lu <aaron.lu@intel.com> Cc: Andi Kleen <ak@linux.intel.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Hillf Danton <hillf.zj@alibaba-inc.com> Cc: Huang Ying <ying.huang@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Jonathan Corbet <corbet@lwn.net> escreveu: Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Minchan Kim <minchan@kernel.org> Cc: Rik van Riel <riel@redhat.com> Cc: Shaohua Li <shli@kernel.org> Cc: Vladimir Davydov <vdavydov.dev@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/swap_state.c')
-rw-r--r--mm/swap_state.c68
1 files changed, 56 insertions, 12 deletions
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 35d7e0ee1c77..3863acd6189c 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -17,6 +17,7 @@
#include <linux/blkdev.h>
#include <linux/pagevec.h>
#include <linux/migrate.h>
+#include <linux/vmalloc.h>
#include <asm/pgtable.h>
@@ -32,15 +33,8 @@ static const struct address_space_operations swap_aops = {
#endif
};
-struct address_space swapper_spaces[MAX_SWAPFILES] = {
- [0 ... MAX_SWAPFILES - 1] = {
- .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
- .i_mmap_writable = ATOMIC_INIT(0),
- .a_ops = &swap_aops,
- /* swap cache doesn't use writeback related tags */
- .flags = 1 << AS_NO_WRITEBACK_TAGS,
- }
-};
+struct address_space *swapper_spaces[MAX_SWAPFILES];
+static unsigned int nr_swapper_spaces[MAX_SWAPFILES];
#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
@@ -53,11 +47,26 @@ static struct {
unsigned long total_swapcache_pages(void)
{
- int i;
+ unsigned int i, j, nr;
unsigned long ret = 0;
+ struct address_space *spaces;
- for (i = 0; i < MAX_SWAPFILES; i++)
- ret += swapper_spaces[i].nrpages;
+ rcu_read_lock();
+ for (i = 0; i < MAX_SWAPFILES; i++) {
+ /*
+ * The corresponding entries in nr_swapper_spaces and
+ * swapper_spaces will be reused only after at least
+ * one grace period. So it is impossible for them
+ * belongs to different usage.
+ */
+ nr = nr_swapper_spaces[i];
+ spaces = rcu_dereference(swapper_spaces[i]);
+ if (!nr || !spaces)
+ continue;
+ for (j = 0; j < nr; j++)
+ ret += spaces[j].nrpages;
+ }
+ rcu_read_unlock();
return ret;
}
@@ -505,3 +514,38 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
skip:
return read_swap_cache_async(entry, gfp_mask, vma, addr);
}
+
+int init_swap_address_space(unsigned int type, unsigned long nr_pages)
+{
+ struct address_space *spaces, *space;
+ unsigned int i, nr;
+
+ nr = DIV_ROUND_UP(nr_pages, SWAP_ADDRESS_SPACE_PAGES);
+ spaces = vzalloc(sizeof(struct address_space) * nr);
+ if (!spaces)
+ return -ENOMEM;
+ for (i = 0; i < nr; i++) {
+ space = spaces + i;
+ INIT_RADIX_TREE(&space->page_tree, GFP_ATOMIC|__GFP_NOWARN);
+ atomic_set(&space->i_mmap_writable, 0);
+ space->a_ops = &swap_aops;
+ /* swap cache doesn't use writeback related tags */
+ mapping_set_no_writeback_tags(space);
+ spin_lock_init(&space->tree_lock);
+ }
+ nr_swapper_spaces[type] = nr;
+ rcu_assign_pointer(swapper_spaces[type], spaces);
+
+ return 0;
+}
+
+void exit_swap_address_space(unsigned int type)
+{
+ struct address_space *spaces;
+
+ spaces = swapper_spaces[type];
+ nr_swapper_spaces[type] = 0;
+ rcu_assign_pointer(swapper_spaces[type], NULL);
+ synchronize_rcu();
+ kvfree(spaces);
+}