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    SubjectRe: [PATCH 3/4] writeback, memcg: Implement cgroup_writeback_by_id()
    On Sat 03-08-19 07:01:54, 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.
    >
    > Signed-off-by: Tejun Heo <tj@kernel.org>
    > ---
    > fs/fs-writeback.c | 64 +++++++++++++++++++++++++++++++++++++++
    > include/linux/writeback.h | 4 +++
    > 2 files changed, 68 insertions(+)
    >
    > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
    > index 6129debdc938..5c79d7acefdb 100644
    > --- a/fs/fs-writeback.c
    > +++ b/fs/fs-writeback.c
    > @@ -880,6 +880,70 @@ static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
    > wb_put(last_wb);
    > }
    >
    > +/**
    > + * 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
    > + * @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 */
    > + wb = wb_get_create(bdi, memcg_css, GFP_NOWAIT | __GFP_NOWARN);
    > + if (!wb) {
    > + ret = -ENOMEM;
    > + goto out_css_put;
    > + }
    > +
    > + /* 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->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
    > *
    > diff --git a/include/linux/writeback.h b/include/linux/writeback.h
    > index 8945aac31392..ad794f2a7d42 100644
    > --- a/include/linux/writeback.h
    > +++ b/include/linux/writeback.h
    > @@ -217,6 +217,10 @@ void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
    > 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);
    > +int writeback_by_id(int id, unsigned long nr, enum wb_reason reason,
    > + struct wb_completion *done);

    I guess this writeback_by_id() is stale? I didn't find it anywhere else...

    Honza
    --
    Jan Kara <jack@suse.com>
    SUSE Labs, CR

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