zram: add algo parameter support to zram_recompress()

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

Link: https://lkml.kernel.org/r/20221109115047.2921851-11-senozhatsky@chromium.orgSigned-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Alexey Romanov <avromanov@sberdevices.ru>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Suleiman Souhlal <suleiman@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

drivers/block/zram/zram_drv.c

@@ -1674,6 +1674,7 @@ 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;
 
@@ -1708,6 +1709,7 @@ 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);
@@ -1740,13 +1742,19 @@ 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;
 	}
 
@@ -1795,10 +1803,11 @@ 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;
@@ -1830,6 +1839,11 @@ static ssize_t recompress_store(struct device *dev,
 				return ret;
 			continue;
 		}
+
+		if (!strcmp(param, "algo")) {
+			algo = val;
+			continue;
+		}
 	}
 
 	if (threshold >= PAGE_SIZE)
@@ -1841,6 +1855,26 @@ 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;
@@ -1871,7 +1905,7 @@ 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) {
@@ -2107,6 +2141,7 @@ static void zram_destroy_comps(struct zram *zram)
 		if (!comp)
 			continue;
 		zcomp_destroy(comp);
+		zram->num_active_comps--;
 	}
 }
 
@@ -2174,6 +2209,7 @@ 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);

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
 	 */