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authorDan Williams <dan.j.williams@intel.com>2019-05-14 15:41:35 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2019-05-14 19:52:48 -0700
commit97500a4a54876d3d6d2d1b8419223eb4e69b32d8 (patch)
tree2b9362cd0411e7ef29e6dd45d4189cc6fa0f58fb /mm/shuffle.c
parentb03641af680959df57c275a80ff0dc116627c7ae (diff)
mm: maintain randomization of page free lists
When freeing a page with an order >= shuffle_page_order randomly select the front or back of the list for insertion. While the mm tries to defragment physical pages into huge pages this can tend to make the page allocator more predictable over time. Inject the front-back randomness to preserve the initial randomness established by shuffle_free_memory() when the kernel was booted. The overhead of this manipulation is constrained by only being applied for MAX_ORDER sized pages by default. [akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/154899812788.3165233.9066631950746578517.stgit@dwillia2-desk3.amr.corp.intel.com Signed-off-by: Dan Williams <dan.j.williams@intel.com> Reviewed-by: Kees Cook <keescook@chromium.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Keith Busch <keith.busch@intel.com> Cc: Robert Elliott <elliott@hpe.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/shuffle.c')
-rw-r--r--mm/shuffle.c23
1 files changed, 23 insertions, 0 deletions
diff --git a/mm/shuffle.c b/mm/shuffle.c
index bc0419a61fbe..3ce12481b1dc 100644
--- a/mm/shuffle.c
+++ b/mm/shuffle.c
@@ -182,3 +182,26 @@ void __meminit __shuffle_free_memory(pg_data_t *pgdat)
for (z = pgdat->node_zones; z < pgdat->node_zones + MAX_NR_ZONES; z++)
shuffle_zone(z);
}
+
+void add_to_free_area_random(struct page *page, struct free_area *area,
+ int migratetype)
+{
+ static u64 rand;
+ static u8 rand_bits;
+
+ /*
+ * The lack of locking is deliberate. If 2 threads race to
+ * update the rand state it just adds to the entropy.
+ */
+ if (rand_bits == 0) {
+ rand_bits = 64;
+ rand = get_random_u64();
+ }
+
+ if (rand & 1)
+ add_to_free_area(page, area, migratetype);
+ else
+ add_to_free_area_tail(page, area, migratetype);
+ rand_bits--;
+ rand >>= 1;
+}