{
struct rmap_item *rmap_item;
- rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
+ rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL |
+ __GFP_NORETRY | __GFP_NOWARN);
if (rmap_item)
ksm_rmap_items++;
return rmap_item;
return 0;
}
- 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 {
+ /*
+ * Page could be still mapped if this races with __mmput() running in
+ * between ksm_exit() and exit_mmap(). Just refuse to let
+ * merge_across_nodes/max_page_sharing be switched.
+ */
+ err = -EBUSY;
+ if (!page_mapped(page)) {
/*
* The stable node did not yet appear stale to get_ksm_page(),
* since that allows for an unmapped ksm page to be recognized
tree_rmap_item =
unstable_tree_search_insert(rmap_item, page, &tree_page);
if (tree_rmap_item) {
+ bool split;
+
kpage = try_to_merge_two_pages(rmap_item, page,
tree_rmap_item, tree_page);
+ /*
+ * If both pages we tried to merge belong to the same compound
+ * page, then we actually ended up increasing the reference
+ * count of the same compound page twice, and split_huge_page
+ * failed.
+ * Here we set a flag if that happened, and we use it later to
+ * try split_huge_page again. Since we call put_page right
+ * afterwards, the reference count will be correct and
+ * split_huge_page should succeed.
+ */
+ split = PageTransCompound(page)
+ && compound_head(page) == compound_head(tree_page);
put_page(tree_page);
if (kpage) {
/*
break_cow(tree_rmap_item);
break_cow(rmap_item);
}
+ } else if (split) {
+ /*
+ * We are here if we tried to merge two pages and
+ * failed because they both belonged to the same
+ * compound page. We will split the page now, but no
+ * merging will take place.
+ * We do not want to add the cost of a full lock; if
+ * the page is locked, it is better to skip it and
+ * perhaps try again later.
+ */
+ if (!trylock_page(page))
+ return;
+ split_huge_page(page);
+ unlock_page(page);
}
}
}