Hi Kamezawa-san,
thanks for your reply.
KAMEZAWA Hiroyuki wrote:
> Interesting, but how about adjust this parameter like below instead of
> adding new control knob ?(this kind of knob is not easy to use.)
>
> ==
> struct writeback_control wbc = {
> .bdi = bdi,
> .sync_mode = WB_SYNC_NONE,
> .older_than_this = NULL,
> .nr_to_write = 0,
> .range_cyclic = 1,
> };
> <snip>
> if (nr_reclaimable) {
> /* Just do what I can do */
> dirty_pages_on_device =
> count_dirty_pages_on_device_limited(bdi, writechunk);
> wbc.nr_to_write = dirty_pages_on_device.
> writeback_inodes(&wbc);
>
> ==
>
> count_dirty_pages_on_device_limited(bdi, writechunk) above returns
> dirty pages on bdi. if # of dirty_pages on bdi is larger than writechunk,
> just returns writechunk.
I think that way is not enough to control the total amount of
Dirty+Writeback.
In that way, while writeback_inodes() scans for dirty pages and writes
them back, the caller will be blocked only if the length of the write-
requests queue is longer than nr_requests. If so, Writeback may consume
tens MB memory for each queue, because nr_requests is 128 and the
maximum size of a request is 512KB. If you have several devices, it can
consume more than hundred MB memory.
I concerned about that, so I introduced dirty_limit_ratio to limit the
total amount of Dirty+Writeback pages.
Regards
--
Tomoki Sekiyama
Hitachi, Ltd., Systems Development Laboratory
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