The patch titled
Subject: zram: introduce recompress sysfs knob
has been added to the -mm mm-unstable branch. Its filename is
zram-introduce-recompress-sysfs-knob.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/zram-introduce-recompress-sysfs-knob.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
Subject: zram: introduce recompress sysfs knob
Date: Tue, 18 Oct 2022 13:55:28 +0900
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 (in bytes) 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
Link: https://lkml.kernel.org/r/20221018045533.2396670-5-senozhatsky@xxxxxxxxxxxx
Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Nitin Gupta <ngupta@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/block/zram/Kconfig | 15 ++
drivers/block/zram/zram_drv.c | 196 +++++++++++++++++++++++++++++++-
drivers/block/zram/zram_drv.h | 2
3 files changed, 210 insertions(+), 3 deletions(-)
--- a/drivers/block/zram/Kconfig~zram-introduce-recompress-sysfs-knob
+++ a/drivers/block/zram/Kconfig
@@ -78,3 +78,18 @@ 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/huge pages, using a potentially slower but
+ more effective compression algorithm. Note, that IDLE page support
+ requires ZRAM_MEMORY_TRACKING.
+
+ echo TIMEOUT > /sys/block/zramX/idle
+ echo SIZE > /sys/block/zramX/recompress
+
+ SIZE (in bytes) parameter sets the object size watermark: idle
+ objects that are of a smaller size will not get recompressed.
--- a/drivers/block/zram/zram_drv.c~zram-introduce-recompress-sysfs-knob
+++ a/drivers/block/zram/zram_drv.c
@@ -1279,6 +1279,12 @@ static void zram_free_page(struct zram *
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_RECOMP_SKIP))
+ zram_clear_flag(zram, index, ZRAM_RECOMP_SKIP);
+
if (zram_test_flag(zram, index, ZRAM_WB)) {
zram_clear_flag(zram, index, ZRAM_WB);
free_block_bdev(zram, zram_get_element(zram, index));
@@ -1340,6 +1346,7 @@ static int zram_read_from_zspool(struct
unsigned long handle;
unsigned int size;
void *src, *dst;
+ u32 idx;
int ret;
handle = zram_get_handle(zram, index);
@@ -1356,8 +1363,13 @@ static int zram_read_from_zspool(struct
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) {
@@ -1369,7 +1381,7 @@ static int zram_read_from_zspool(struct
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;
@@ -1600,6 +1612,182 @@ out:
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 the object so that we
+ * don't attempt to re-compress it again (RECOMP_SKIP).
+ */
+ if (comp_len_next >= huge_class_size ||
+ comp_len_next >= comp_len_prev ||
+ ret) {
+ zram_set_flag(zram, index, ZRAM_RECOMP_SKIP);
+ 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 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_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 PTR_ERR((void *)handle_next);
+ }
+
+ 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;
+ 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 -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 = 0;
+
+ 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) ||
+ zram_test_flag(zram, index, ZRAM_RECOMP_SKIP))
+ goto next;
+
+ err = zram_recompress(zram, index, page, size_watermark);
+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
@@ -1980,6 +2168,7 @@ static DEVICE_ATTR_RW(writeback_limit_en
#endif
#ifdef CONFIG_ZRAM_MULTI_COMP
static DEVICE_ATTR_RW(recomp_algorithm);
+static DEVICE_ATTR_WO(recompress);
#endif
static struct attribute *zram_disk_attrs[] = {
@@ -2006,6 +2195,7 @@ 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,
};
--- a/drivers/block/zram/zram_drv.h~zram-introduce-recompress-sysfs-knob
+++ a/drivers/block/zram/zram_drv.h
@@ -49,6 +49,8 @@ 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 */
+ ZRAM_RECOMP_SKIP, /* secondary algorithm cannot compress this page */
__NR_ZRAM_PAGEFLAGS,
};
_
Patches currently in -mm which might be from senozhatsky@xxxxxxxxxxxx are
zram-preparation-for-multi-zcomp-support.patch
zram-add-recompression-algorithm-sysfs-knob.patch
zram-factor-out-wb-and-non-wb-zram-read-functions.patch
zram-introduce-recompress-sysfs-knob.patch
documentation-add-recompression-documentation.patch
zram-add-recompression-algorithm-choice-to-kconfig.patch
zram-add-recompress-flag-to-read_block_state.patch
zram-clarify-writeback_store-comment.patch
zram-use-is_err_value-to-check-for-zs_malloc-errors.patch
