[PATCHv5 10/13] zram: Add algo parameter support to zram_recompress()

[Sergey Senozhatsky]

Recompression iterates through all the registered secondary
compression algorithms in order of their priorities so that
we have higher chances of finding the algorithm that compresses
a particular page. This, however, may not always be best
approach and sometimes we may want to limit recompression to
only one particular algorithm. For instance, when a higher
priority algorithm uses too much power and device has a
relatively low battery level we may want to limit recompression
to use only a lower priority algorithm, which uses less power.

Introduce algo= parameter support to recompression sysfs knob
so that user-sapce can request recompression with particular
algorithm only:

  echo "type=idle algo=zstd" > /sys/block/zramX/recompress

Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
---
 drivers/block/zram/zram_drv.c | 54 +++++++++++++++++++++++++++++------
 drivers/block/zram/zram_drv.h |  1 +
 2 files changed, 46 insertions(+), 9 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 67b58f2255db..89d25f60b33e 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1677,6 +1677,7 @@ static int zram_recompress(struct zram *zram, u32 index, struct page *page,
 	unsigned int comp_len_new;
 	unsigned int class_index_old;
 	unsigned int class_index_new;
+	u32 num_recomps = 0;
 	void *src, *dst;
 	int ret;
 
@@ -1711,6 +1712,7 @@ static int zram_recompress(struct zram *zram, u32 index, struct page *page,
 		if (prio <= zram_get_priority(zram, index))
 			continue;
 
+		num_recomps++;
 		zstrm = zcomp_stream_get(zram->comps[prio]);
 		src = kmap_atomic(page);
 		ret = zcomp_compress(zstrm, src, &comp_len_new);
@@ -1743,13 +1745,19 @@ static int zram_recompress(struct zram *zram, u32 index, struct page *page,
 	if (!zstrm)
 		return 0;
 
-	/*
-	 * All secondary algorithms failed to re-compress the page in a way
-	 * that would save memory, mark the object as incompressible so that
-	 * we will not try to compress it again.
-	 */
 	if (class_index_new >= class_index_old) {
-		zram_set_flag(zram, index, ZRAM_INCOMPRESSIBLE);
+		/*
+		 * Secondary algorithms failed to re-compress the page
+		 * in a way that would save memory, mark the object as
+		 * incompressible so that we will not try to compress
+		 * it again.
+		 *
+		 * We need to make sure that all secondary algorithms have
+		 * failed, so we test if the number of recompressions matches
+		 * the number of active secondary algorithms.
+		 */
+		if (num_recomps == zram->num_active_comps - 1)
+			zram_set_flag(zram, index, ZRAM_INCOMPRESSIBLE);
 		return 0;
 	}
 
@@ -1798,10 +1806,11 @@ static ssize_t recompress_store(struct device *dev,
 				struct device_attribute *attr,
 				const char *buf, size_t len)
 {
+	u32 prio = ZRAM_SECONDARY_COMP, prio_max = ZRAM_MAX_COMPS;
 	struct zram *zram = dev_to_zram(dev);
-	u32 mode = 0, threshold = 0, prio = ZRAM_SECONDARY_COMP;
 	unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
-	char *args, *param, *val;
+	char *args, *param, *val, *algo = NULL;
+	u32 mode = 0, threshold = 0;
 	unsigned long index;
 	struct page *page;
 	ssize_t ret;
@@ -1833,6 +1842,11 @@ static ssize_t recompress_store(struct device *dev,
 				return ret;
 			continue;
 		}
+
+		if (!strcmp(param, "algo")) {
+			algo = val;
+			continue;
+		}
 	}
 
 	if (threshold >= PAGE_SIZE)
@@ -1844,6 +1858,26 @@ static ssize_t recompress_store(struct device *dev,
 		goto release_init_lock;
 	}
 
+	if (algo) {
+		bool found = false;
+
+		for (; prio < ZRAM_MAX_COMPS; prio++) {
+			if (!zram->comp_algs[prio])
+				continue;
+
+			if (!strcmp(zram->comp_algs[prio], algo)) {
+				prio_max = min(prio + 1, ZRAM_MAX_COMPS);
+				found = true;
+				break;
+			}
+		}
+
+		if (!found) {
+			ret = -EINVAL;
+			goto release_init_lock;
+		}
+	}
+
 	page = alloc_page(GFP_KERNEL);
 	if (!page) {
 		ret = -ENOMEM;
@@ -1874,7 +1908,7 @@ static ssize_t recompress_store(struct device *dev,
 			goto next;
 
 		err = zram_recompress(zram, index, page, threshold,
-				      prio, ZRAM_MAX_COMPS);
+				      prio, prio_max);
 next:
 		zram_slot_unlock(zram, index);
 		if (err) {
@@ -2110,6 +2144,7 @@ static void zram_destroy_comps(struct zram *zram)
 		if (!comp)
 			continue;
 		zcomp_destroy(comp);
+		zram->num_active_comps--;
 	}
 }
 
@@ -2177,6 +2212,7 @@ static ssize_t disksize_store(struct device *dev,
 		}
 
 		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 b80faae76835..473325415a74 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -125,6 +125,7 @@ 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
 	 */
-- 
2.38.1.431.g37b22c650d-goog