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Subject[PATCHv3 2/2] zram: drop max_zpage_size and use zs_huge_class_size()
Date
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>

This patch removes ZRAM's enforced "huge object" value and uses zsmalloc
huge-class watermark instead, which makes more sense.

TEST
- I used a 1G zram device, LZO compression back-end, original
data set size was 444MB. Looking at zsmalloc classes stats the
test ended up to be pretty fair.

BASE ZRAM/ZSMALLOC
=====================
zram mm_stat

498978816 191482495 199831552 0 199831552 15634 0

zsmalloc classes

class size almost_full almost_empty obj_allocated obj_used pages_used pages_per_zspage freeable
...
151 2448 0 0 1240 1240 744 3 0
168 2720 0 0 4200 4200 2800 2 0
190 3072 0 0 10100 10100 7575 3 0
202 3264 0 0 380 380 304 4 0
254 4096 0 0 10620 10620 10620 1 0

Total 7 46 106982 106187 48787 0

PATCHED ZRAM/ZSMALLOC
=====================

zram mm_stat

498978816 182579184 194248704 0 194248704 15628 0

zsmalloc classes

class size almost_full almost_empty obj_allocated obj_used pages_used pages_per_zspage freeable
...
151 2448 0 0 1240 1240 744 3 0
168 2720 0 0 4200 4200 2800 2 0
190 3072 0 0 10100 10100 7575 3 0
202 3264 0 0 7180 7180 5744 4 0
254 4096 0 0 3820 3820 3820 1 0

Total 8 45 106959 106193 47424 0

As we can see, we reduced the number of objects stored in class-4096,
because a huge number of objects which we previously forcibly stored in
class-4096 now stored in non-huge class-3264. This results in lower
memory consumption:

- zsmalloc now uses 47424 physical pages, which is less than 48787 pages
zsmalloc used before.

- objects that we store in class-3264 share zspages. That's why overall
the number of pages that both class-4096 and class-3264 consumed went
down from 10924 to 9564.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
---
drivers/block/zram/zram_drv.c | 9 ++++++++-
drivers/block/zram/zram_drv.h | 16 ----------------
2 files changed, 8 insertions(+), 17 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 71b449613cfa..0f3fadd71230 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -44,6 +44,11 @@ static const char *default_compressor = "lzo";

/* Module params (documentation at end) */
static unsigned int num_devices = 1;
+/*
+ * Pages that compress to sizes equals or greater than this are stored
+ * uncompressed in memory.
+ */
+static size_t huge_class_size;

static void zram_free_page(struct zram *zram, size_t index);

@@ -786,6 +791,8 @@ static bool zram_meta_alloc(struct zram *zram, u64 disksize)
return false;
}

+ if (!huge_class_size)
+ huge_class_size = zs_huge_class_size(zram->mem_pool);
return true;
}

@@ -965,7 +972,7 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
return ret;
}

- if (unlikely(comp_len > max_zpage_size)) {
+ if (unlikely(comp_len >= huge_class_size)) {
if (zram_wb_enabled(zram) && allow_wb) {
zcomp_stream_put(zram->comp);
ret = write_to_bdev(zram, bvec, index, bio, &element);
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 31762db861e3..d71c8000a964 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -21,22 +21,6 @@

#include "zcomp.h"

-/*-- Configurable parameters */
-
-/*
- * Pages that compress to size greater than this are stored
- * uncompressed in memory.
- */
-static const size_t max_zpage_size = PAGE_SIZE / 4 * 3;
-
-/*
- * NOTE: max_zpage_size must be less than or equal to:
- * ZS_MAX_ALLOC_SIZE. Otherwise, zs_malloc() would
- * always return failure.
- */
-
-/*-- End of configurable params */
-
#define SECTOR_SHIFT 9
#define SECTORS_PER_PAGE_SHIFT (PAGE_SHIFT - SECTOR_SHIFT)
#define SECTORS_PER_PAGE (1 << SECTORS_PER_PAGE_SHIFT)
--
2.16.2
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