It's not entirely correct to use ->num_active_comps for
max-prio limit, as ->num_active_comps just tells the
number of configured algorithms, not the max configured
priority.  For instance, in the following theoretical
example:

    [lz4] [nil] [nil] [deflate]

->num_active_comps is 2, while the actual max-prio is 3.

Drop ->num_active_comps and use ZRAM_MAX_COMPS instead.

Suggested-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 drivers/block/zram/zram_drv.c | 29 ++++++++++++++++-------------
 drivers/block/zram/zram_drv.h |  1 -
 2 files changed, 16 insertions(+), 14 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 53e0bbf9d6ec..6ca5a76c3865 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -2371,6 +2371,18 @@ static int scan_slots_for_recompress(struct zram *zram, u32 mode, u32 prio_max,
 	return 0;
 }
 
+static bool highest_priority_algorithm(struct zram *zram, u32 prio)
+{
+	u32 p;
+
+	for (p = prio + 1; p < ZRAM_MAX_COMPS; p++) {
+		if (zram->comp_algs[p])
+			return false;
+	}
+
+	return true;
+}
+
 /*
  * This function will decompress (unless it's ZRAM_HUGE) the page and then
  * attempt to compress it using provided compression algorithm priority
@@ -2478,12 +2490,11 @@ static int recompress_slot(struct zram *zram, u32 index, struct page *page,
 		 * Secondary algorithms failed to re-compress the page
 		 * in a way that would save memory.
 		 *
-		 * Mark the object incompressible if the max-priority
-		 * algorithm couldn't re-compress it.
+		 * Mark the object incompressible if the max-priority (the
+		 * last configured one) algorithm couldn't re-compress it.
 		 */
-		if (prio < zram->num_active_comps)
-			return 0;
-		set_slot_flag(zram, index, ZRAM_INCOMPRESSIBLE);
+		if (highest_priority_algorithm(zram, prio))
+			set_slot_flag(zram, index, ZRAM_INCOMPRESSIBLE);
 		return 0;
 	}
 
@@ -2615,12 +2626,6 @@ static ssize_t recompress_store(struct device *dev,
 		}
 	}
 
-	prio_max = min(prio_max, (u32)zram->num_active_comps);
-	if (prio >= prio_max) {
-		ret = -EINVAL;
-		goto out;
-	}
-
 	if (prio < ZRAM_SECONDARY_COMP || prio >= ZRAM_MAX_COMPS) {
 		ret = -EINVAL;
 		goto out;
@@ -2833,7 +2838,6 @@ static void zram_destroy_comps(struct zram *zram)
 		if (!comp)
 			continue;
 		zcomp_destroy(comp);
-		zram->num_active_comps--;
 	}
 
 	for (prio = ZRAM_PRIMARY_COMP; prio < ZRAM_MAX_COMPS; prio++)
@@ -2898,7 +2902,6 @@ static ssize_t disksize_store(struct device *dev, struct device_attribute *attr,
 		}
 
 		zram->comps[prio] = comp;
-		zram->num_active_comps++;
 	}
 	zram->disksize = disksize;
 	set_capacity_and_notify(zram->disk, zram->disksize >> SECTOR_SHIFT);
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index f0de8f8218f5..08d1774c15db 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -125,7 +125,6 @@ struct zram {
 	 */
 	u64 disksize;	/* bytes */
 	const char *comp_algs[ZRAM_MAX_COMPS];
-	s8 num_active_comps;
 	/*
 	 * zram is claimed so open request will be failed
 	 */
-- 
2.53.0.473.g4a7958ca14-goog