Commit 97500a4a authored by Dan Williams's avatar Dan Williams Committed by Linus Torvalds
Browse files

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: default avatarDan Williams <dan.j.williams@intel.com>
Reviewed-by: default avatarKees 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b03641af

include/linux/mmzone.h

+12 −0
Original line number Diff line number Diff line
@@ -116,6 +116,18 @@ static inline void add_to_free_area_tail(struct page *page, struct free_area *ar 
	area->nr_free++;

}



#ifdef CONFIG_SHUFFLE_PAGE_ALLOCATOR

/* Used to preserve page allocation order entropy */

void add_to_free_area_random(struct page *page, struct free_area *area,

		int migratetype);

#else

static inline void add_to_free_area_random(struct page *page,

		struct free_area *area, int migratetype)

{

	add_to_free_area(page, area, migratetype);

}

#endif



/* Used for pages which are on another list */

static inline void move_to_free_area(struct page *page, struct free_area *area,

			     int migratetype)

mm/page_alloc.c

+9 −2
Original line number Diff line number Diff line
@@ -43,6 +43,7 @@ 
#include <linux/mempolicy.h>

#include <linux/memremap.h>

#include <linux/stop_machine.h>

#include <linux/random.h>

#include <linux/sort.h>

#include <linux/pfn.h>

#include <linux/backing-dev.h>
@@ -958,7 +959,8 @@ done_merging: 
	 * so it's less likely to be used soon and more likely to be merged

	 * as a higher order page

	 */

	if ((order < MAX_ORDER-2) && pfn_valid_within(buddy_pfn)) {

	if ((order < MAX_ORDER-2) && pfn_valid_within(buddy_pfn)

			&& !is_shuffle_order(order)) {

		struct page *higher_page, *higher_buddy;

		combined_pfn = buddy_pfn & pfn;

		higher_page = page + (combined_pfn - pfn);
@@ -972,7 +974,12 @@ done_merging: 
		}

	}



	if (is_shuffle_order(order))

		add_to_free_area_random(page, &zone->free_area[order],

				migratetype);

	else

		add_to_free_area(page, &zone->free_area[order], migratetype);



}



/*

mm/shuffle.c

+23 −0
Original line number Diff line number Diff line
@@ -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;

}

mm/shuffle.h

+12 −0
Original line number Diff line number Diff line
@@ -36,6 +36,13 @@ static inline void shuffle_zone(struct zone *z) 
		return;

	__shuffle_zone(z);

}



static inline bool is_shuffle_order(int order)

{

	if (!static_branch_unlikely(&page_alloc_shuffle_key))

		return false;

	return order >= SHUFFLE_ORDER;

}

#else

static inline void shuffle_free_memory(pg_data_t *pgdat)

{
@@ -48,5 +55,10 @@ static inline void shuffle_zone(struct zone *z) 
static inline void page_alloc_shuffle(enum mm_shuffle_ctl ctl)

{

}



static inline bool is_shuffle_order(int order)

{

	return false;

}

#endif

#endif /* _MM_SHUFFLE_H */

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