On Wed 21-08-19 14:02:10, Tejun Heo wrote:
> Implement cgroup_writeback_by_id() which initiates cgroup writeback
> from bdi and memcg IDs. This will be used by memcg foreign inode
> flushing.
>
> v2: Use wb_get_lookup() instead of wb_get_create() to avoid creating
> spurious wbs.
>
> v3: Interpret 0 @nr as 1.25 * nr_dirty to implement best-effort
> flushing while avoding possible livelocks.
>
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
The patch looks good to me. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> fs/fs-writeback.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/writeback.h | 2 +
> 2 files changed, 85 insertions(+)
>
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -892,6 +892,89 @@ restart:
> }
>
> /**
> + * cgroup_writeback_by_id - initiate cgroup writeback from bdi and memcg IDs
> + * @bdi_id: target bdi id
> + * @memcg_id: target memcg css id
> + * @nr_pages: number of pages to write, 0 for best-effort dirty flushing
> + * @reason: reason why some writeback work initiated
> + * @done: target wb_completion
> + *
> + * Initiate flush of the bdi_writeback identified by @bdi_id and @memcg_id
> + * with the specified parameters.
> + */
> +int cgroup_writeback_by_id(u64 bdi_id, int memcg_id, unsigned long nr,
> + enum wb_reason reason, struct wb_completion *done)
> +{
> + struct backing_dev_info *bdi;
> + struct cgroup_subsys_state *memcg_css;
> + struct bdi_writeback *wb;
> + struct wb_writeback_work *work;
> + int ret;
> +
> + /* lookup bdi and memcg */
> + bdi = bdi_get_by_id(bdi_id);
> + if (!bdi)
> + return -ENOENT;
> +
> + rcu_read_lock();
> + memcg_css = css_from_id(memcg_id, &memory_cgrp_subsys);
> + if (memcg_css && !css_tryget(memcg_css))
> + memcg_css = NULL;
> + rcu_read_unlock();
> + if (!memcg_css) {
> + ret = -ENOENT;
> + goto out_bdi_put;
> + }
> +
> + /*
> + * And find the associated wb. If the wb isn't there already
> + * there's nothing to flush, don't create one.
> + */
> + wb = wb_get_lookup(bdi, memcg_css);
> + if (!wb) {
> + ret = -ENOENT;
> + goto out_css_put;
> + }
> +
> + /*
> + * If @nr is zero, the caller is attempting to write out most of
> + * the currently dirty pages. Let's take the current dirty page
> + * count and inflate it by 25% which should be large enough to
> + * flush out most dirty pages while avoiding getting livelocked by
> + * concurrent dirtiers.
> + */
> + if (!nr) {
> + unsigned long filepages, headroom, dirty, writeback;
> +
> + mem_cgroup_wb_stats(wb, &filepages, &headroom, &dirty,
> + &writeback);
> + nr = dirty * 10 / 8;
> + }
> +
> + /* issue the writeback work */
> + work = kzalloc(sizeof(*work), GFP_NOWAIT | __GFP_NOWARN);
> + if (work) {
> + work->nr_pages = nr;
> + work->sync_mode = WB_SYNC_NONE;
> + work->range_cyclic = 1;
> + work->reason = reason;
> + work->done = done;
> + work->auto_free = 1;
> + wb_queue_work(wb, work);
> + ret = 0;
> + } else {
> + ret = -ENOMEM;
> + }
> +
> + wb_put(wb);
> +out_css_put:
> + css_put(memcg_css);
> +out_bdi_put:
> + bdi_put(bdi);
> + return ret;
> +}
> +
> +/**
> * cgroup_writeback_umount - flush inode wb switches for umount
> *
> * This function is called when a super_block is about to be destroyed and
> --- a/include/linux/writeback.h
> +++ b/include/linux/writeback.h
> @@ -217,6 +217,8 @@ void wbc_attach_and_unlock_inode(struct
> void wbc_detach_inode(struct writeback_control *wbc);
> void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page,
> size_t bytes);
> +int cgroup_writeback_by_id(u64 bdi_id, int memcg_id, unsigned long nr_pages,
> + enum wb_reason reason, struct wb_completion *done);
> void cgroup_writeback_umount(void);
>
> /**
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
