linux-kernel - Re: [PATCH 3/4] writeback, memcg: Implement cgroup_writeback_by

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Date:   Thu, 15 Aug 2019 16:05:35 +0200
From:   Jan Kara <jack@...e.cz>
To:     Tejun Heo <tj@...nel.org>
Cc:     axboe@...nel.dk, jack@...e.cz, hannes@...xchg.org,
        mhocko@...nel.org, vdavydov.dev@...il.com, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com, guro@...com,
        akpm@...ux-foundation.org
Subject: Re: [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@...nel.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@...e.com>
SUSE Labs, CR