[PATCH 1/3][resend] use lock for 64-bit stats

[Nitin Gupta <ngupta@vflare.org>]

64-bit stats corruption was observed when ramzswap was
used on SMP systems. To prevent this, use separate spinlock
to protect these stats.

Also, replace stat_*() with rzs_stat*() to avoid possible
conflict with core kernel code.

Eventually, these will be converted to per-cpu counters
if this driver finds use on large scale systems and this
locking is found to affect scalability.

Signed-off-by: Nitin Gupta <ngupta@vflare.org>
---
 drivers/staging/ramzswap/ramzswap_drv.c   |   58 +++++++++++++++--------------
 drivers/staging/ramzswap/ramzswap_drv.h   |   59 ++++++++++++++++++++++++-----
 drivers/staging/ramzswap/ramzswap_ioctl.h |    1 +
 3 files changed, 80 insertions(+), 38 deletions(-)

diff --git a/drivers/staging/ramzswap/ramzswap_drv.c b/drivers/staging/ramzswap/ramzswap_drv.c
index baf7572..05273c0 100644
--- a/drivers/staging/ramzswap/ramzswap_drv.c
+++ b/drivers/staging/ramzswap/ramzswap_drv.c
@@ -24,7 +24,6 @@
 #include <linux/genhd.h>
 #include <linux/highmem.h>
 #include <linux/lzo.h>
-#include <linux/mutex.h>
 #include <linux/string.h>
 #include <linux/swap.h>
 #include <linux/swapops.h>
@@ -239,7 +238,8 @@ void ramzswap_ioctl_get_stats(struct ramzswap *rzs,

 	mem_used = xv_get_total_size_bytes(rzs->mem_pool)
 			+ (rs->pages_expand << PAGE_SHIFT);
-	succ_writes = rs->num_writes - rs->failed_writes;
+	succ_writes = rzs_stat64_read(rzs, &rs->num_writes) -
+			rzs_stat64_read(rzs, &rs->failed_writes);

 	if (succ_writes && rs->pages_stored) {
 		good_compress_perc = rs->good_compress * 100
@@ -248,11 +248,12 @@ void ramzswap_ioctl_get_stats(struct ramzswap *rzs,
 					/ rs->pages_stored;
 	}

-	s->num_reads = rs->num_reads;
-	s->num_writes = rs->num_writes;
-	s->failed_reads = rs->failed_reads;
-	s->failed_writes = rs->failed_writes;
-	s->invalid_io = rs->invalid_io;
+	s->num_reads = rzs_stat64_read(rzs, &rs->num_reads);
+	s->num_writes = rzs_stat64_read(rzs, &rs->num_writes);
+	s->failed_reads = rzs_stat64_read(rzs, &rs->failed_reads);
+	s->failed_writes = rzs_stat64_read(rzs, &rs->failed_writes);
+	s->invalid_io = rzs_stat64_read(rzs, &rs->invalid_io);
+	s->notify_free = rzs_stat64_read(rzs, &rs->notify_free);
 	s->pages_zero = rs->pages_zero;

 	s->good_compress_pct = good_compress_perc;
@@ -264,8 +265,8 @@ void ramzswap_ioctl_get_stats(struct ramzswap *rzs,
 	s->compr_data_size = rs->compr_size;
 	s->mem_used_total = mem_used;

-	s->bdev_num_reads = rs->bdev_num_reads;
-	s->bdev_num_writes = rs->bdev_num_writes;
+	s->bdev_num_reads = rzs_stat64_read(rzs, &rs->bdev_num_reads);
+	s->bdev_num_writes = rzs_stat64_read(rzs, &rs->bdev_num_writes);
 	}
 #endif /* CONFIG_RAMZSWAP_STATS */
 }
@@ -594,7 +595,7 @@ static void ramzswap_free_page(struct ramzswap *rzs, size_t index)
 	if (unlikely(!page)) {
 		if (rzs_test_flag(rzs, index, RZS_ZERO)) {
 			rzs_clear_flag(rzs, index, RZS_ZERO);
-			stat_dec(rzs->stats.pages_zero);
+			rzs_stat_dec(&rzs->stats.pages_zero);
 		}
 		return;
 	}
@@ -603,7 +604,7 @@ static void ramzswap_free_page(struct ramzswap *rzs, size_t index)
 		clen = PAGE_SIZE;
 		__free_page(page);
 		rzs_clear_flag(rzs, index, RZS_UNCOMPRESSED);
-		stat_dec(rzs->stats.pages_expand);
+		rzs_stat_dec(&rzs->stats.pages_expand);
 		goto out;
 	}

@@ -613,11 +614,11 @@ static void ramzswap_free_page(struct ramzswap *rzs, size_t index)

 	xv_free(rzs->mem_pool, page, offset);
 	if (clen <= PAGE_SIZE / 2)
-		stat_dec(rzs->stats.good_compress);
+		rzs_stat_dec(&rzs->stats.good_compress);

 out:
 	rzs->stats.compr_size -= clen;
-	stat_dec(rzs->stats.pages_stored);
+	rzs_stat_dec(&rzs->stats.pages_stored);

 	rzs->table[index].page = NULL;
 	rzs->table[index].offset = 0;
@@ -679,8 +680,8 @@ static int handle_ramzswap_fault(struct ramzswap *rzs, struct bio *bio)
 	 */
 	if (rzs->backing_swap) {
 		u32 pagenum;
-		stat_dec(rzs->stats.num_reads);
-		stat_inc(rzs->stats.bdev_num_reads);
+		rzs_stat64_dec(rzs, &rzs->stats.num_reads);
+		rzs_stat64_inc(rzs, &rzs->stats.bdev_num_reads);
 		bio->bi_bdev = rzs->backing_swap;

 		/*
@@ -718,7 +719,7 @@ static int ramzswap_read(struct ramzswap *rzs, struct bio *bio)
 	struct zobj_header *zheader;
 	unsigned char *user_mem, *cmem;

-	stat_inc(rzs->stats.num_reads);
+	rzs_stat64_inc(rzs, &rzs->stats.num_reads);

 	page = bio->bi_io_vec[0].bv_page;
 	index = bio->bi_sector >> SECTORS_PER_PAGE_SHIFT;
@@ -752,7 +753,7 @@ static int ramzswap_read(struct ramzswap *rzs, struct bio *bio)
 	if (unlikely(ret != LZO_E_OK)) {
 		pr_err("Decompression failed! err=%d, page=%u\n",
 			ret, index);
-		stat_inc(rzs->stats.failed_reads);
+		rzs_stat64_inc(rzs, &rzs->stats.failed_reads);
 		goto out;
 	}

@@ -776,7 +777,7 @@ static int ramzswap_write(struct ramzswap *rzs, struct bio *bio)
 	struct page *page, *page_store;
 	unsigned char *user_mem, *cmem, *src;

-	stat_inc(rzs->stats.num_writes);
+	rzs_stat64_inc(rzs, &rzs->stats.num_writes);

 	page = bio->bi_io_vec[0].bv_page;
 	index = bio->bi_sector >> SECTORS_PER_PAGE_SHIFT;
@@ -796,7 +797,7 @@ static int ramzswap_write(struct ramzswap *rzs, struct bio *bio)
 	 * Simply clear zero page flag.
 	 */
 	if (rzs_test_flag(rzs, index, RZS_ZERO)) {
-		stat_dec(rzs->stats.pages_zero);
+		rzs_stat_dec(&rzs->stats.pages_zero);
 		rzs_clear_flag(rzs, index, RZS_ZERO);
 	}

@@ -806,7 +807,7 @@ static int ramzswap_write(struct ramzswap *rzs, struct bio *bio)
 	if (page_zero_filled(user_mem)) {
 		kunmap_atomic(user_mem, KM_USER0);
 		mutex_unlock(&rzs->lock);
-		stat_inc(rzs->stats.pages_zero);
+		rzs_stat_inc(&rzs->stats.pages_zero);
 		rzs_set_flag(rzs, index, RZS_ZERO);

 		set_bit(BIO_UPTODATE, &bio->bi_flags);
@@ -830,7 +831,7 @@ static int ramzswap_write(struct ramzswap *rzs, struct bio *bio)
 	if (unlikely(ret != LZO_E_OK)) {
 		mutex_unlock(&rzs->lock);
 		pr_err("Compression failed! err=%d\n", ret);
-		stat_inc(rzs->stats.failed_writes);
+		rzs_stat64_inc(rzs, &rzs->stats.failed_writes);
 		goto out;
 	}

@@ -853,13 +854,13 @@ static int ramzswap_write(struct ramzswap *rzs, struct bio *bio)
 			mutex_unlock(&rzs->lock);
 			pr_info("Error allocating memory for incompressible "
 				"page: %u\n", index);
-			stat_inc(rzs->stats.failed_writes);
+			rzs_stat64_inc(rzs, &rzs->stats.failed_writes);
 			goto out;
 		}

 		offset = 0;
 		rzs_set_flag(rzs, index, RZS_UNCOMPRESSED);
-		stat_inc(rzs->stats.pages_expand);
+		rzs_stat_inc(&rzs->stats.pages_expand);
 		rzs->table[index].page = page_store;
 		src = kmap_atomic(page, KM_USER0);
 		goto memstore;
@@ -871,7 +872,7 @@ static int ramzswap_write(struct ramzswap *rzs, struct bio *bio)
 		mutex_unlock(&rzs->lock);
 		pr_info("Error allocating memory for compressed "
 			"page: %u, size=%zu\n", index, clen);
-		stat_inc(rzs->stats.failed_writes);
+		rzs_stat64_inc(rzs, &rzs->stats.failed_writes);
 		if (rzs->backing_swap)
 			fwd_write_request = 1;
 		goto out;
@@ -900,9 +901,9 @@ memstore:

 	/* Update stats */
 	rzs->stats.compr_size += clen;
-	stat_inc(rzs->stats.pages_stored);
+	rzs_stat_inc(&rzs->stats.pages_stored);
 	if (clen <= PAGE_SIZE / 2)
-		stat_inc(rzs->stats.good_compress);
+		rzs_stat_inc(&rzs->stats.good_compress);

 	mutex_unlock(&rzs->lock);

@@ -912,7 +913,7 @@ memstore:

 out:
 	if (fwd_write_request) {
-		stat_inc(rzs->stats.bdev_num_writes);
+		rzs_stat64_inc(rzs, &rzs->stats.bdev_num_writes);
 		bio->bi_bdev = rzs->backing_swap;
 #if 0
 		/*
@@ -974,7 +975,7 @@ static int ramzswap_make_request(struct request_queue *queue, struct bio *bio)
 	}

 	if (!valid_swap_request(rzs, bio)) {
-		stat_inc(rzs->stats.invalid_io);
+		rzs_stat64_inc(rzs, &rzs->stats.invalid_io);
 		bio_io_error(bio);
 		return 0;
 	}
@@ -1295,6 +1296,7 @@ static struct block_device_operations ramzswap_devops = {
 static int create_device(struct ramzswap *rzs, int device_id)
 {
 	mutex_init(&rzs->lock);
+	spin_lock_init(&rzs->stat64_lock);
 	INIT_LIST_HEAD(&rzs->backing_swap_extent_list);

 	rzs->queue = blk_alloc_queue(GFP_KERNEL);
diff --git a/drivers/staging/ramzswap/ramzswap_drv.h b/drivers/staging/ramzswap/ramzswap_drv.h
index 7ba98bf..5b67222 100644
--- a/drivers/staging/ramzswap/ramzswap_drv.h
+++ b/drivers/staging/ramzswap/ramzswap_drv.h
@@ -15,6 +15,9 @@
 #ifndef _RAMZSWAP_DRV_H_
 #define _RAMZSWAP_DRV_H_

+#include <linux/spinlock.h>
+#include <linux/mutex.h>
+
 #include "ramzswap_ioctl.h"
 #include "xvmalloc.h"

@@ -71,15 +74,6 @@ static const unsigned max_zpage_size_nobdev = PAGE_SIZE / 4 * 3;
 #define SECTORS_PER_PAGE_SHIFT	(PAGE_SHIFT - SECTOR_SHIFT)
 #define SECTORS_PER_PAGE	(1 << SECTORS_PER_PAGE_SHIFT)

-/* Debugging and Stats */
-#if defined(CONFIG_RAMZSWAP_STATS)
-#define stat_inc(stat)	((stat)++)
-#define stat_dec(stat)	((stat)--)
-#else
-#define stat_inc(x)
-#define stat_dec(x)
-#endif
-
 /* Flags for ramzswap pages (table[page_no].flags) */
 enum rzs_pageflags {
 	/* Page is stored uncompressed */
@@ -124,6 +118,7 @@ struct ramzswap_stats {
 	u64 failed_reads;	/* should NEVER! happen */
 	u64 failed_writes;	/* can happen when memory is too low */
 	u64 invalid_io;		/* non-swap I/O requests */
+	u64 notify_free;	/* no. of swap slot free notifications */
 	u32 pages_zero;		/* no. of zero filled pages */
 	u32 pages_stored;	/* no. of pages currently stored */
 	u32 good_compress;	/* % of pages with compression ratio<=50% */
@@ -138,6 +133,7 @@ struct ramzswap {
 	void *compress_workmem;
 	void *compress_buffer;
 	struct table *table;
+	spinlock_t stat64_lock;	/* protect 64-bit stats */
 	struct mutex lock;
 	struct request_queue *queue;
 	struct gendisk *disk;
@@ -167,5 +163,48 @@ struct ramzswap {

 /*-- */

-#endif
+/* Debugging and Stats */
+#if defined(CONFIG_RAMZSWAP_STATS)
+static void rzs_stat_inc(u32 *v)
+{
+	*v = *v + 1;
+}
+
+static void rzs_stat_dec(u32 *v)
+{
+	*v = *v - 1;
+}
+
+static void rzs_stat64_inc(struct ramzswap *rzs, u64 *v)
+{
+	spin_lock(&rzs->stat64_lock);
+	*v = *v + 1;
+	spin_unlock(&rzs->stat64_lock);
+}
+
+static void rzs_stat64_dec(struct ramzswap *rzs, u64 *v)
+{
+	spin_lock(&rzs->stat64_lock);
+	*v = *v - 1;
+	spin_unlock(&rzs->stat64_lock);
+}
+
+static u64 rzs_stat64_read(struct ramzswap *rzs, u64 *v)
+{
+	u64 val;
+
+	spin_lock(&rzs->stat64_lock);
+	val = *v;
+	spin_unlock(&rzs->stat64_lock);
+
+	return val;
+}
+#else
+#define rzs_stat_inc(v)
+#define rzs_stat_dec(v)
+#define rzs_stat64_inc(r, v)
+#define rzs_stat64_dec(r, v)
+#define rzs_stat64_read(r, v)
+#endif /* CONFIG_RAMZSWAP_STATS */

+#endif
diff --git a/drivers/staging/ramzswap/ramzswap_ioctl.h b/drivers/staging/ramzswap/ramzswap_ioctl.h
index 1bc54e2..1edaeba 100644
--- a/drivers/staging/ramzswap/ramzswap_ioctl.h
+++ b/drivers/staging/ramzswap/ramzswap_ioctl.h
@@ -27,6 +27,7 @@ struct ramzswap_ioctl_stats {
 	u64 failed_reads;	/* should NEVER! happen */
 	u64 failed_writes;	/* can happen when memory is too low */
 	u64 invalid_io;		/* non-swap I/O requests */
+	u64 notify_free;	/* no. of swap slot free notifications */
 	u32 pages_zero;		/* no. of zero filled pages */
 	u32 good_compress_pct;	/* no. of pages with compression ratio<=50% */
 	u32 pages_expand_pct;	/* no. of incompressible pages */
--
1.6.2.5