Allow zram to recompress (using secondary compression streams)
pages.
Re-compression algorithms (we support up to 3 at this stage)
are selected via recomp_algorithm:
echo "algo=zstd priority=1" > /sys/block/zramX/recomp_algorithm
Please read documentation for more details.
We support several recompression modes:
1) IDLE pages recompression is activated by `idle` mode
echo "type=idle" > /sys/block/zram0/recompress
2) Since there may be many idle pages user-space may pass a size
threshold value (in bytes) and we will recompress pages only
of equal or greater size:
echo "threshold=888" > /sys/block/zram0/recompress
3) HUGE pages recompression is activated by `huge` mode
echo "type=huge" > /sys/block/zram0/recompress
4) HUGE_IDLE pages recompression is activated by `huge_idle` mode
echo "type=huge_idle" > /sys/block/zram0/recompress
Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
---
drivers/block/zram/Kconfig | 9 ++
drivers/block/zram/zram_drv.c | 264 +++++++++++++++++++++++++++++++++-
drivers/block/zram/zram_drv.h | 7 +
3 files changed, 277 insertions(+), 3 deletions(-)
diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
index d4100b0c083e..0386b7da02aa 100644
--- a/drivers/block/zram/Kconfig
+++ b/drivers/block/zram/Kconfig
@@ -78,3 +78,12 @@ config ZRAM_MEMORY_TRACKING
/sys/kernel/debug/zram/zramX/block_state.
See Documentation/admin-guide/blockdev/zram.rst for more information.
+
+config ZRAM_MULTI_COMP
+ bool "Enable multiple compression streams"
+ depends on ZRAM
+ help
+ This will enable multi-compression streams, so that ZRAM can
+ re-compress pages using a potentially slower but more effective
+ compression algorithm. Note, that IDLE page recompression
+ requires ZRAM_MEMORY_TRACKING.
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index a6a5fd2474d7..749e4266dd72 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -155,6 +155,25 @@ static inline bool is_partial_io(struct bio_vec *bvec)
}
#endif
+static inline void zram_set_priority(struct zram *zram, u32 index, u32 prio)
+{
+ prio &= ZRAM_COMP_PRIORITY_MASK;
+ /*
+ * Clear previous priority value first, in case if we recompress
+ * further an already recompressed page
+ */
+ zram->table[index].flags &= ~(ZRAM_COMP_PRIORITY_MASK <<
+ ZRAM_COMP_PRIORITY_BIT1);
+ zram->table[index].flags |= (prio << ZRAM_COMP_PRIORITY_BIT1);
+}
+
+static inline u32 zram_get_priority(struct zram *zram, u32 index)
+{
+ u32 prio = zram->table[index].flags >> ZRAM_COMP_PRIORITY_BIT1;
+
+ return prio & ZRAM_COMP_PRIORITY_MASK;
+}
+
/*
* Check if request is within bounds and aligned on zram logical blocks.
*/
@@ -1307,6 +1326,11 @@ static void zram_free_page(struct zram *zram, size_t index)
atomic64_dec(&zram->stats.huge_pages);
}
+ if (zram_test_flag(zram, index, ZRAM_INCOMPRESSIBLE))
+ zram_clear_flag(zram, index, ZRAM_INCOMPRESSIBLE);
+
+ zram_set_priority(zram, index, 0);
+
if (zram_test_flag(zram, index, ZRAM_WB)) {
zram_clear_flag(zram, index, ZRAM_WB);
free_block_bdev(zram, zram_get_element(zram, index));
@@ -1367,6 +1391,7 @@ static int zram_read_from_zspool(struct zram *zram, struct page *page,
unsigned long handle;
unsigned int size;
void *src, *dst;
+ u32 prio;
int ret;
handle = zram_get_handle(zram, index);
@@ -1383,8 +1408,10 @@ static int zram_read_from_zspool(struct zram *zram, struct page *page,
size = zram_get_obj_size(zram, index);
- if (size != PAGE_SIZE)
- zstrm = zcomp_stream_get(zram->comps[ZRAM_PRIMARY_COMP]);
+ if (size != PAGE_SIZE) {
+ prio = zram_get_priority(zram, index);
+ zstrm = zcomp_stream_get(zram->comps[prio]);
+ }
src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
if (size == PAGE_SIZE) {
@@ -1396,7 +1423,7 @@ static int zram_read_from_zspool(struct zram *zram, struct page *page,
dst = kmap_atomic(page);
ret = zcomp_decompress(zstrm, src, size, dst);
kunmap_atomic(dst);
- zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]);
+ zcomp_stream_put(zram->comps[prio]);
}
zs_unmap_object(zram->mem_pool, handle);
return ret;
@@ -1627,6 +1654,235 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
return ret;
}
+#ifdef CONFIG_ZRAM_MULTI_COMP
+/*
+ * This function will decompress (unless it's ZRAM_HUGE) the page and then
+ * attempt to compress it using provided compression algorithm priority
+ * (which is potentially more effective).
+ *
+ * Corresponding ZRAM slot should be locked.
+ */
+static int zram_recompress(struct zram *zram, u32 index, struct page *page,
+ u32 threshold, u32 prio, u32 prio_max)
+{
+ struct zcomp_strm *zstrm = NULL;
+ unsigned long handle_old;
+ unsigned long handle_new;
+ unsigned int comp_len_old;
+ unsigned int comp_len_new;
+ void *src, *dst;
+ int ret;
+
+ handle_old = zram_get_handle(zram, index);
+ if (!handle_old)
+ return -EINVAL;
+
+ comp_len_old = zram_get_obj_size(zram, index);
+ /*
+ * Do not recompress objects that are already "small enough".
+ */
+ if (comp_len_old < threshold)
+ return 0;
+
+ ret = zram_read_from_zspool(zram, page, index);
+ if (ret)
+ return ret;
+
+ /*
+ * Iterate the secondary comp algorithms list (in order of priority)
+ * and try to recompress the page.
+ */
+ for (; prio < prio_max; prio++) {
+ if (!zram->comps[prio])
+ continue;
+
+ /*
+ * Skip if the object is already re-compressed with a higher
+ * priority algorithm (or same algorithm).
+ */
+ if (prio <= zram_get_priority(zram, index))
+ continue;
+
+ zstrm = zcomp_stream_get(zram->comps[prio]);
+ src = kmap_atomic(page);
+ ret = zcomp_compress(zstrm, src, &comp_len_new);
+ kunmap_atomic(src);
+
+ if (ret) {
+ zcomp_stream_put(zram->comps[prio]);
+ return ret;
+ }
+
+ /* Continue until we make progress */
+ if (comp_len_new >= huge_class_size ||
+ comp_len_new >= comp_len_old ||
+ (threshold && comp_len_new >= threshold)) {
+ zcomp_stream_put(zram->comps[prio]);
+ continue;
+ }
+
+ /* Recompression was successful so break out */
+ break;
+ }
+
+ /*
+ * We did not try to recompress, e.g. when we have only one
+ * secondary algorithm and the page is already recompressed
+ * using that algorithm
+ */
+ 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 (comp_len_new >= huge_class_size || comp_len_new >= comp_len_old) {
+ zram_set_flag(zram, index, ZRAM_INCOMPRESSIBLE);
+ return 0;
+ }
+
+ /* Successful recompression but above threshold */
+ if (threshold && comp_len_new >= threshold)
+ return 0;
+
+ /*
+ * No direct reclaim (slow path) for handle allocation and no
+ * re-compression attempt (unlike in __zram_bvec_write()) since
+ * we already have stored that object in zsmalloc. If we cannot
+ * alloc memory for recompressed object then we bail out and
+ * simply keep the old (existing) object in zsmalloc.
+ */
+ handle_new = zs_malloc(zram->mem_pool, comp_len_new,
+ __GFP_KSWAPD_RECLAIM |
+ __GFP_NOWARN |
+ __GFP_HIGHMEM |
+ __GFP_MOVABLE);
+ if (IS_ERR_VALUE(handle_new)) {
+ zcomp_stream_put(zram->comps[prio]);
+ return PTR_ERR((void *)handle_new);
+ }
+
+ dst = zs_map_object(zram->mem_pool, handle_new, ZS_MM_WO);
+ memcpy(dst, zstrm->buffer, comp_len_new);
+ zcomp_stream_put(zram->comps[prio]);
+
+ zs_unmap_object(zram->mem_pool, handle_new);
+
+ zram_free_page(zram, index);
+ zram_set_handle(zram, index, handle_new);
+ zram_set_obj_size(zram, index, comp_len_new);
+ zram_set_priority(zram, index, prio);
+
+ atomic64_add(comp_len_new, &zram->stats.compr_data_size);
+ atomic64_inc(&zram->stats.pages_stored);
+
+ return 0;
+}
+
+#define RECOMPRESS_IDLE (1 << 0)
+#define RECOMPRESS_HUGE (1 << 1)
+
+static ssize_t recompress_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t len)
+{
+ 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;
+ unsigned long index;
+ struct page *page;
+ ssize_t ret;
+
+ args = skip_spaces(buf);
+ while (*args) {
+ args = next_arg(args, ¶m, &val);
+
+ if (!*val)
+ return -EINVAL;
+
+ if (!strcmp(param, "type")) {
+ if (!strcmp(val, "idle"))
+ mode = RECOMPRESS_IDLE;
+ if (!strcmp(val, "huge"))
+ mode = RECOMPRESS_HUGE;
+ if (!strcmp(val, "huge_idle"))
+ mode = RECOMPRESS_IDLE | RECOMPRESS_HUGE;
+ continue;
+ }
+
+ if (!strcmp(param, "threshold")) {
+ /*
+ * We will re-compress only idle objects equal or
+ * greater in size than watermark.
+ */
+ ret = kstrtouint(val, 10, &threshold);
+ if (ret)
+ return ret;
+ continue;
+ }
+ }
+
+ if (threshold >= PAGE_SIZE)
+ return -EINVAL;
+
+ down_read(&zram->init_lock);
+ if (!init_done(zram)) {
+ ret = -EINVAL;
+ goto release_init_lock;
+ }
+
+ page = alloc_page(GFP_KERNEL);
+ if (!page) {
+ ret = -ENOMEM;
+ goto release_init_lock;
+ }
+
+ ret = len;
+ for (index = 0; index < nr_pages; index++) {
+ int err;
+
+ zram_slot_lock(zram, index);
+
+ if (!zram_allocated(zram, index))
+ goto next;
+
+ if (mode & RECOMPRESS_IDLE &&
+ !zram_test_flag(zram, index, ZRAM_IDLE))
+ goto next;
+
+ if (mode & RECOMPRESS_HUGE &&
+ !zram_test_flag(zram, index, ZRAM_HUGE))
+ goto next;
+
+ if (zram_test_flag(zram, index, ZRAM_WB) ||
+ zram_test_flag(zram, index, ZRAM_UNDER_WB) ||
+ zram_test_flag(zram, index, ZRAM_SAME) ||
+ zram_test_flag(zram, index, ZRAM_INCOMPRESSIBLE))
+ goto next;
+
+ err = zram_recompress(zram, index, page, threshold,
+ prio, ZRAM_MAX_COMPS);
+next:
+ zram_slot_unlock(zram, index);
+ if (err) {
+ ret = err;
+ break;
+ }
+
+ cond_resched();
+ }
+
+ __free_page(page);
+
+release_init_lock:
+ up_read(&zram->init_lock);
+ return ret;
+}
+#endif
+
/*
* zram_bio_discard - handler on discard request
* @index: physical block index in PAGE_SIZE units
@@ -2006,6 +2262,7 @@ static DEVICE_ATTR_RW(writeback_limit_enable);
#endif
#ifdef CONFIG_ZRAM_MULTI_COMP
static DEVICE_ATTR_RW(recomp_algorithm);
+static DEVICE_ATTR_WO(recompress);
#endif
static struct attribute *zram_disk_attrs[] = {
@@ -2032,6 +2289,7 @@ static struct attribute *zram_disk_attrs[] = {
&dev_attr_debug_stat.attr,
#ifdef CONFIG_ZRAM_MULTI_COMP
&dev_attr_recomp_algorithm.attr,
+ &dev_attr_recompress.attr,
#endif
NULL,
};
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 7a643c8c38ec..b80faae76835 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -40,6 +40,9 @@
*/
#define ZRAM_FLAG_SHIFT (PAGE_SHIFT + 1)
+/* Only 2 bits are allowed for comp priority index */
+#define ZRAM_COMP_PRIORITY_MASK 0x3
+
/* Flags for zram pages (table[page_no].flags) */
enum zram_pageflags {
/* zram slot is locked */
@@ -49,6 +52,10 @@ enum zram_pageflags {
ZRAM_UNDER_WB, /* page is under writeback */
ZRAM_HUGE, /* Incompressible page */
ZRAM_IDLE, /* not accessed page since last idle marking */
+ ZRAM_INCOMPRESSIBLE, /* none of the algorithms could compress it */
+
+ ZRAM_COMP_PRIORITY_BIT1, /* First bit of comp priority index */
+ ZRAM_COMP_PRIORITY_BIT2, /* Second bit of comp priority index */
__NR_ZRAM_PAGEFLAGS,
};
--
2.38.1.431.g37b22c650d-goog
