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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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