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Date: Mon, 5 Sep 2022 17:15:49 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Minchan Kim <minchan@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: Nitin Gupta <ngupta@...are.org>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: [PATCH RFC 4/7] zram: Introduce recompress sysfs knob
Allow zram to recompress (using secondary compression streams)
pages. We support three modes:
1) IDLE pages recompression is activated by `idle` mode
echo idle > /sys/block/zram0/recompress
2) Since there may be many idle pages user-space may pass a size
watermark value and we will recompress IDLE pages only of equal
or greater size:
echo 888 > /sys/block/zram0/recompress
3) HUGE pages recompression is activated by `huge` mode
echo huge > /sys/block/zram0/recompress
4) HUGE_IDLE pages recompression is activated by `huge_idle` mode
echo huge_idle > /sys/block/zram0/recompress
Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
---
drivers/block/zram/Kconfig | 11 ++
drivers/block/zram/zram_drv.c | 191 +++++++++++++++++++++++++++++++++-
drivers/block/zram/zram_drv.h | 1 +
3 files changed, 200 insertions(+), 3 deletions(-)
diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
index d4100b0c083e..81ae4b96ec1a 100644
--- a/drivers/block/zram/Kconfig
+++ b/drivers/block/zram/Kconfig
@@ -78,3 +78,14 @@ 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 per-CPU compression streams"
+ depends on ZRAM
+ help
+ This will enable per-CPU multi-compression streams, so that ZRAM
+ can re-compress IDLE pages, using a potentially slower but more
+ effective compression algorithm.
+
+ echo TIMEOUT > /sys/block/zramX/idle
+ echo SIZE > /sys/block/zramX/recompress
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index de2970865b7b..386e49a13806 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1293,6 +1293,9 @@ static void zram_free_page(struct zram *zram, size_t index)
atomic64_dec(&zram->stats.huge_pages);
}
+ if (zram_test_flag(zram, index, ZRAM_RECOMP))
+ zram_clear_flag(zram, index, ZRAM_RECOMP);
+
if (zram_test_flag(zram, index, ZRAM_WB)) {
zram_clear_flag(zram, index, ZRAM_WB);
free_block_bdev(zram, zram_get_element(zram, index));
@@ -1357,6 +1360,7 @@ static int zram_read_from_zspool(struct zram *zram,
unsigned long handle;
unsigned int size;
void *src, *dst;
+ u32 idx;
int ret;
handle = zram_get_handle(zram, index);
@@ -1373,8 +1377,13 @@ static int zram_read_from_zspool(struct zram *zram,
size = zram_get_obj_size(zram, index);
- if (size != PAGE_SIZE)
- zstrm = zcomp_stream_get(zram->comps[ZRAM_PRIMARY_ZCOMP]);
+ if (size != PAGE_SIZE) {
+ idx = ZRAM_PRIMARY_ZCOMP;
+ if (zram_test_flag(zram, index, ZRAM_RECOMP))
+ idx = ZRAM_SECONDARY_ZCOMP;
+
+ zstrm = zcomp_stream_get(zram->comps[idx]);
+ }
src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
if (size == PAGE_SIZE) {
@@ -1386,7 +1395,7 @@ static int zram_read_from_zspool(struct zram *zram,
dst = kmap_atomic(page);
ret = zcomp_decompress(zstrm, src, size, dst);
kunmap_atomic(dst);
- zcomp_stream_put(zram->comps[ZRAM_PRIMARY_ZCOMP]);
+ zcomp_stream_put(zram->comps[idx]);
}
zs_unmap_object(zram->mem_pool, handle);
return ret;
@@ -1612,6 +1621,180 @@ 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 secondary compression algorithm (which is
+ * potentially more effective).
+ *
+ * Corresponding ZRAM slot should be locked.
+ */
+static int zram_recompress(struct zram *zram,
+ u32 index,
+ struct page *page,
+ int size_watermark)
+{
+ unsigned long handle_prev;
+ unsigned long handle_next;
+ unsigned int comp_len_next;
+ unsigned int comp_len_prev;
+ struct zcomp_strm *zstrm;
+ void *src, *dst;
+ int ret;
+
+ handle_prev = zram_get_handle(zram, index);
+ if (!handle_prev)
+ return -EINVAL;
+
+ comp_len_prev = zram_get_obj_size(zram, index);
+ /*
+ * Do not recompress objects that are already "small enough".
+ */
+ if (comp_len_prev < size_watermark)
+ return 0;
+
+ ret = zram_read_from_zspool(zram, page, index);
+ if (ret)
+ return ret;
+
+ zstrm = zcomp_stream_get(zram->comps[ZRAM_SECONDARY_ZCOMP]);
+ src = kmap_atomic(page);
+ ret = zcomp_compress(zstrm, src, &comp_len_next);
+ kunmap_atomic(src);
+
+ /*
+ * Either a compression error or we failed to compressed the object
+ * in a way that will save us memory. Mark object as "recompressed"
+ * if it's huge, so that we don't try to recompress it again. Ideally
+ * we want to set some bit for all such objects, but we for now do so
+ * only for huge ones (we are out of bits in flags on 32-bit systems).
+ */
+ if (comp_len_next >= huge_class_size ||
+ comp_len_next >= comp_len_prev ||
+ ret) {
+ if (zram_test_flag(zram, index, ZRAM_HUGE))
+ zram_set_flag(zram, index, ZRAM_RECOMP);
+ zram_clear_flag(zram, index, ZRAM_IDLE);
+ zcomp_stream_put(zram->comps[ZRAM_SECONDARY_ZCOMP]);
+ return ret;
+ }
+
+ /*
+ * No direct reclaim (slow path) for handle allocation and no
+ * re-compression attempt (unlike in __zram_bvec_write()) since
+ * we already stored that object in zsmalloc. If we cannot alloc
+ * memory then me bail out.
+ */
+ handle_next = zs_malloc(zram->mem_pool, comp_len_next,
+ __GFP_KSWAPD_RECLAIM |
+ __GFP_NOWARN |
+ __GFP_HIGHMEM |
+ __GFP_MOVABLE);
+ if (IS_ERR((void *)handle_next)) {
+ zcomp_stream_put(zram->comps[ZRAM_SECONDARY_ZCOMP]);
+ return -ENOMEM;
+ }
+
+ dst = zs_map_object(zram->mem_pool, handle_next, ZS_MM_WO);
+ memcpy(dst, zstrm->buffer, comp_len_next);
+ zcomp_stream_put(zram->comps[ZRAM_SECONDARY_ZCOMP]);
+
+ zs_unmap_object(zram->mem_pool, handle_next);
+
+ zram_free_page(zram, index);
+ zram_set_handle(zram, index, handle_next);
+ zram_set_obj_size(zram, index, comp_len_next);
+
+ zram_set_flag(zram, index, ZRAM_RECOMP);
+ atomic64_add(comp_len_next, &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);
+ unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
+ unsigned long index;
+ struct page *page;
+ ssize_t ret = 0;
+ int mode, size_watermark = 0;
+
+ if (sysfs_streq(buf, "idle")) {
+ mode = RECOMPRESS_IDLE;
+ } else if (sysfs_streq(buf, "huge")) {
+ mode = RECOMPRESS_HUGE;
+ } else if (sysfs_streq(buf, "huge_idle")) {
+ mode = RECOMPRESS_IDLE | RECOMPRESS_HUGE;
+ } else {
+ /*
+ * We will re-compress only idle objects equal or greater
+ * in size than watermark.
+ */
+ ret = kstrtoint(buf, 10, &size_watermark);
+ if (ret)
+ return ret;
+ mode = RECOMPRESS_IDLE;
+ }
+
+ if (size_watermark > PAGE_SIZE)
+ return ret;
+
+ 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;
+ }
+
+ for (index = 0; index < nr_pages; index++) {
+ 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_RECOMP))
+ goto next;
+
+ ret = zram_recompress(zram, index, page, size_watermark);
+next:
+ zram_slot_unlock(zram, index);
+ if (ret)
+ break;
+ }
+
+ ret = len;
+ __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
@@ -2001,6 +2184,7 @@ 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[] = {
@@ -2027,6 +2211,7 @@ 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 af3d6f6bfcff..b4eecef2a11f 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -50,6 +50,7 @@ enum zram_pageflags {
ZRAM_UNDER_WB, /* page is under writeback */
ZRAM_HUGE, /* Incompressible page */
ZRAM_IDLE, /* not accessed page since last idle marking */
+ ZRAM_RECOMP, /* page was recompressed */
__NR_ZRAM_PAGEFLAGS,
};
--
2.37.2.789.g6183377224-goog
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