On (12/03/18 11:40), Minchan Kim wrote:
[..]
> +     down_read(&zram->init_lock);
> +     atomic64_set(&zram->stats.bd_wb_limit, val);
> +     if (val == 0)
> +             zram->stop_writeback = false;
> +     up_read(&zram->init_lock);

[..]

> +             if (zram->stop_writeback) {
> +                     ret = -EIO;
> +                     break;
> +             }
> +
>               if (!blk_idx) {
>                       blk_idx = alloc_block_bdev(zram);
>                       if (!blk_idx) {
> @@ -694,6 +732,11 @@ static ssize_t writeback_store(struct device *dev,
>               zram_set_element(zram, index, blk_idx);
>               blk_idx = 0;
>               atomic64_inc(&zram->stats.pages_stored);
> +             if (atomic64_add_unless(&zram->stats.bd_wb_limit,
> +                                     -1 << (PAGE_SHIFT - 12), 0)) {
> +                     if (atomic64_read(&zram->stats.bd_wb_limit) == 0)
> +                             zram->stop_writeback = true;
> +             }

Do we need ->stop_writeback? It should be identical to

        atomic64_read(&zram->stats.bd_wb_limit) == 0


Otherwise, looks good!

        -ss

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