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SubjectRe: [PATCH v4 7/7] zram: writeback throttle
On (12/03/18 14:50), Sergey Senozhatsky wrote:
> 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

Seems like I misread writeback_limit_store() a bit.

So, if I want to, say, let only 10M of writteback pages, I need to
do

echo 0 > writeback_limit
echo 10M > writeback_limit_store // memparse format is for
// simplicity only; I know
// it should be in 4K units.

every day. How about dropping the "echo 0" and ->stop_writeback?
So then we can just do

echo 10M > writeback_limit_store

every day: if we have ->bd_wb_limit budget then we writeback,
otherwise we don't.

-ss

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