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    Subject[PATCH v2 1/4] zsmalloc: move pages_allocated to zs_pool
    Date
    Pages_allocated has counted in size_class structure and when user
    want to see total_size_bytes, it gathers all of value from each
    size_class to report the sum.

    It's not bad if user don't see the value often but if user start
    to see the value frequently, it would be not a good deal for
    performance POV.

    This patch moves the variable from size_class to zs_pool so it would
    reduce memory footprint (from [255 * 8byte] to [sizeof(atomic_t)])
    but it adds new locking overhead but it wouldn't be severe because
    it's not a hot path in zs_malloc(ie, it is called only when new
    zspage is created, not a object).

    Signed-off-by: Minchan Kim <minchan@kernel.org>
    ---
    mm/zsmalloc.c | 30 ++++++++++++++++--------------
    1 file changed, 16 insertions(+), 14 deletions(-)

    diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
    index 94f38fac5e81..a65924255763 100644
    --- a/mm/zsmalloc.c
    +++ b/mm/zsmalloc.c
    @@ -199,9 +199,6 @@ struct size_class {

    spinlock_t lock;

    - /* stats */
    - u64 pages_allocated;
    -
    struct page *fullness_list[_ZS_NR_FULLNESS_GROUPS];
    };

    @@ -217,9 +214,12 @@ struct link_free {
    };

    struct zs_pool {
    + spinlock_t stat_lock;
    +
    struct size_class size_class[ZS_SIZE_CLASSES];

    gfp_t flags; /* allocation flags used when growing pool */
    + unsigned long pages_allocated;
    };

    /*
    @@ -967,6 +967,7 @@ struct zs_pool *zs_create_pool(gfp_t flags)

    }

    + spin_lock_init(&pool->stat_lock);
    pool->flags = flags;

    return pool;
    @@ -1028,8 +1029,10 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
    return 0;

    set_zspage_mapping(first_page, class->index, ZS_EMPTY);
    + spin_lock(&pool->stat_lock);
    + pool->pages_allocated += class->pages_per_zspage;
    + spin_unlock(&pool->stat_lock);
    spin_lock(&class->lock);
    - class->pages_allocated += class->pages_per_zspage;
    }

    obj = (unsigned long)first_page->freelist;
    @@ -1082,14 +1085,14 @@ void zs_free(struct zs_pool *pool, unsigned long obj)

    first_page->inuse--;
    fullness = fix_fullness_group(pool, first_page);
    -
    - if (fullness == ZS_EMPTY)
    - class->pages_allocated -= class->pages_per_zspage;
    -
    spin_unlock(&class->lock);

    - if (fullness == ZS_EMPTY)
    + if (fullness == ZS_EMPTY) {
    + spin_lock(&pool->stat_lock);
    + pool->pages_allocated -= class->pages_per_zspage;
    + spin_unlock(&pool->stat_lock);
    free_zspage(first_page);
    + }
    }
    EXPORT_SYMBOL_GPL(zs_free);

    @@ -1185,12 +1188,11 @@ EXPORT_SYMBOL_GPL(zs_unmap_object);

    u64 zs_get_total_size_bytes(struct zs_pool *pool)
    {
    - int i;
    - u64 npages = 0;
    -
    - for (i = 0; i < ZS_SIZE_CLASSES; i++)
    - npages += pool->size_class[i].pages_allocated;
    + u64 npages;

    + spin_lock(&pool->stat_lock);
    + npages = pool->pages_allocated;
    + spin_unlock(&pool->stat_lock);
    return npages << PAGE_SHIFT;
    }
    EXPORT_SYMBOL_GPL(zs_get_total_size_bytes);
    --
    2.0.0


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