diff options
| -rw-r--r-- | Documentation/vm/ksm.txt | 16 | ||||
| -rw-r--r-- | mm/ksm.c | 18 |
2 files changed, 26 insertions, 8 deletions
diff --git a/Documentation/vm/ksm.txt b/Documentation/vm/ksm.txt index 25cc89ba811..f34a8ee6f86 100644 --- a/Documentation/vm/ksm.txt +++ b/Documentation/vm/ksm.txt @@ -60,10 +60,18 @@ sleep_millisecs - how many milliseconds ksmd should sleep before next scan merge_across_nodes - specifies if pages from different numa nodes can be merged. When set to 0, ksm merges only pages which physically - reside in the memory area of same NUMA node. It brings - lower latency to access to shared page. Value can be - changed only when there is no ksm shared pages in system. - Default: 1 + reside in the memory area of same NUMA node. That brings + lower latency to access of shared pages. Systems with more + nodes, at significant NUMA distances, are likely to benefit + from the lower latency of setting 0. Smaller systems, which + need to minimize memory usage, are likely to benefit from + the greater sharing of setting 1 (default). You may wish to + compare how your system performs under each setting, before + deciding on which to use. merge_across_nodes setting can be + changed only when there are no ksm shared pages in system: + set run 2 to unmerge pages first, then to 1 after changing + merge_across_nodes, to remerge according to the new setting. + Default: 1 (merging across nodes as in earlier releases) run - set 0 to stop ksmd from running but keep merged pages, set 1 to run ksmd e.g. "echo 1 > /sys/kernel/mm/ksm/run", @@ -87,6 +87,9 @@ * take 10 attempts to find a page in the unstable tree, once it is found, * it is secured in the stable tree. (When we scan a new page, we first * compare it against the stable tree, and then against the unstable tree.) + * + * If the merge_across_nodes tunable is unset, then KSM maintains multiple + * stable trees and multiple unstable trees: one of each for each NUMA node. */ /** @@ -526,7 +529,7 @@ static void remove_node_from_stable_tree(struct stable_node *stable_node) * a page to put something that might look like our key in page->mapping. * is on its way to being freed; but it is an anomaly to bear in mind. */ -static struct page *get_ksm_page(struct stable_node *stable_node, bool locked) +static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it) { struct page *page; void *expected_mapping; @@ -575,7 +578,7 @@ again: goto stale; } - if (locked) { + if (lock_it) { lock_page(page); if (ACCESS_ONCE(page->mapping) != expected_mapping) { unlock_page(page); @@ -705,10 +708,17 @@ static int remove_stable_node(struct stable_node *stable_node) return 0; } - if (WARN_ON_ONCE(page_mapped(page))) + if (WARN_ON_ONCE(page_mapped(page))) { + /* + * This should not happen: but if it does, just refuse to let + * merge_across_nodes be switched - there is no need to panic. + */ err = -EBUSY; - else { + } else { /* + * The stable node did not yet appear stale to get_ksm_page(), + * since that allows for an unmapped ksm page to be recognized + * right up until it is freed; but the node is safe to remove. * This page might be in a pagevec waiting to be freed, * or it might be PageSwapCache (perhaps under writeback), * or it might have been removed from swapcache a moment ago. |