On (12/24/18 12:35), Minchan Kim wrote:
[..]
> @@ -645,10 +680,13 @@ static ssize_t writeback_store(struct device *dev,
> bvec.bv_len = PAGE_SIZE;
> bvec.bv_offset = 0;
>
> - if (zram->stop_writeback) {
> + spin_lock(&zram->wb_limit_lock);
> + if (zram->wb_limit_enable && !zram->bd_wb_limit) {
> + spin_unlock(&zram->wb_limit_lock);
> ret = -EIO;
> break;
> }
> + spin_unlock(&zram->wb_limit_lock);
[..]
> @@ -732,11 +771,10 @@ 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;
> - }
> + spin_lock(&zram->wb_limit_lock);
> + if (zram->wb_limit_enable && zram->bd_wb_limit > 0)
> + zram->bd_wb_limit -= 1UL << (PAGE_SHIFT - 12);
> + spin_unlock(&zram->wb_limit_lock);
Do we really need ->wb_limit_lock spinlock? We kinda punch it twice
in this loop. If someone clears ->wb_limit_enable somewhere in between
then the worst thing to happen is that we will just write extra page
to the backing device; not a very big deal to me. Am I missing
something?
-ss
