[PATCH v4 3/3] mm: fs: Invalidate BH LRU during page migration

Minchan Kim
2021-03-19T17:52:45Z

Pages containing buffer_heads that are in one of the per-CPU
buffer_head LRU caches will be pinned and thus cannot be migrated.
This can prevent CMA allocations from succeeding, which are often used
on platforms with co-processors (such as a DSP) that can only use
physically contiguous memory. It can also prevent memory
hot-unplugging from succeeding, which involves migrating at least
MIN_MEMORY_BLOCK_SIZE bytes of memory, which ranges from 8 MiB to 1
GiB based on the architecture in use.

Correspondingly, invalidate the BH LRU caches before a migration
starts and stop any buffer_head from being cached in the LRU caches,
until migration has finished.

Tested-by: Oliver Sang <oliver.sang@intel.com>
Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Chris Goldsworthy <cgoldswo@codeaurora.org>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
fs/buffer.c | 36 ++++++++++++++++++++++++++++++------
include/linux/buffer_head.h | 4 ++++
mm/swap.c | 5 ++++-
3 files changed, 38 insertions(+), 7 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 0cb7ffd4977c..e9872d0dcbf1 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1264,6 +1264,15 @@ static void bh_lru_install(struct buffer_head *bh)
int i;

check_irqs_on();
+ /*
+ * the refcount of buffer_head in bh_lru prevents dropping the
+ * attached page(i.e., try_to_free_buffers) so it could cause
+ * failing page migration.
+ * Skip putting upcoming bh into bh_lru until migration is done.
+ */
+ if (lru_cache_disabled())
+ return;
+
bh_lru_lock();

b = this_cpu_ptr(&bh_lrus);
@@ -1404,6 +1413,15 @@ __bread_gfp(struct block_device *bdev, sector_t block,
}
EXPORT_SYMBOL(__bread_gfp);

+static void __invalidate_bh_lrus(struct bh_lru *b)
+{
+ int i;
+
+ for (i = 0; i < BH_LRU_SIZE; i++) {
+ brelse(b->bhs[i]);
+ b->bhs[i] = NULL;
+ }
+}
/*
* invalidate_bh_lrus() is called rarely - but not only at unmount.
* This doesn't race because it runs in each cpu either in irq
@@ -1412,16 +1430,12 @@ EXPORT_SYMBOL(__bread_gfp);
static void invalidate_bh_lru(void *arg)
{
struct bh_lru *b = &get_cpu_var(bh_lrus);
- int i;

- for (i = 0; i < BH_LRU_SIZE; i++) {
- brelse(b->bhs[i]);
- b->bhs[i] = NULL;
- }
+ __invalidate_bh_lrus(b);
put_cpu_var(bh_lrus);
}

-static bool has_bh_in_lru(int cpu, void *dummy)
+bool has_bh_in_lru(int cpu, void *dummy)
{
struct bh_lru *b = per_cpu_ptr(&bh_lrus, cpu);
int i;
@@ -1440,6 +1454,16 @@ void invalidate_bh_lrus(void)
}
EXPORT_SYMBOL_GPL(invalidate_bh_lrus);

+void invalidate_bh_lrus_cpu(int cpu)
+{
+ struct bh_lru *b;
+
+ bh_lru_lock();
+ b = per_cpu_ptr(&bh_lrus, cpu);
+ __invalidate_bh_lrus(b);
+ bh_lru_unlock();
+}
+
void set_bh_page(struct buffer_head *bh,
struct page *page, unsigned long offset)
{
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 6b47f94378c5..e7e99da31349 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -194,6 +194,8 @@ void __breadahead_gfp(struct block_device *, sector_t block, unsigned int size,
struct buffer_head *__bread_gfp(struct block_device *,
sector_t block, unsigned size, gfp_t gfp);
void invalidate_bh_lrus(void);
+void invalidate_bh_lrus_cpu(int cpu);
+bool has_bh_in_lru(int cpu, void *dummy);
struct buffer_head *alloc_buffer_head(gfp_t gfp_flags);
void free_buffer_head(struct buffer_head * bh);
void unlock_buffer(struct buffer_head *bh);
@@ -406,6 +408,8 @@ static inline int inode_has_buffers(struct inode *inode) { return 0; }
static inline void invalidate_inode_buffers(struct inode *inode) {}
static inline int remove_inode_buffers(struct inode *inode) { return 1; }
static inline int sync_mapping_buffers(struct address_space *mapping) { return 0; }
+static inline void invalidate_bh_lrus_cpu(int cpu) {}
+static inline bool has_bh_in_lru(int cpu, void *dummy) { return 0; }
#define buffer_heads_over_limit 0

#endif /* CONFIG_BLOCK */
diff --git a/mm/swap.c b/mm/swap.c
index c94f55e7b649..a75a8265302b 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -36,6 +36,7 @@
#include <linux/hugetlb.h>
#include <linux/page_idle.h>
#include <linux/local_lock.h>
+#include <linux/buffer_head.h>

#include "internal.h"

@@ -641,6 +642,7 @@ void lru_add_drain_cpu(int cpu)
pagevec_lru_move_fn(pvec, lru_lazyfree_fn);

activate_page_drain(cpu);
+ invalidate_bh_lrus_cpu(cpu);
}

/**
@@ -828,7 +830,8 @@ inline void __lru_add_drain_all(bool force_all_cpus)
pagevec_count(&per_cpu(lru_pvecs.lru_deactivate_file, cpu)) ||
pagevec_count(&per_cpu(lru_pvecs.lru_deactivate, cpu)) ||
pagevec_count(&per_cpu(lru_pvecs.lru_lazyfree, cpu)) ||
- need_activate_page_drain(cpu)) {
+ need_activate_page_drain(cpu) ||
+ has_bh_in_lru(cpu, NULL)) {
INIT_WORK(work, lru_add_drain_per_cpu);
queue_work_on(cpu, mm_percpu_wq, work);
__cpumask_set_cpu(cpu, &has_work);
--
2.31.0.rc2.261.g7f71774620-goog