Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit d62241c7 authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
Browse files

writeback, memcg: Implement cgroup_writeback_by_id() 



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.

Reviewed-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent ed288dc0

fs/fs-writeback.c

+83 −0
Original line number Diff line number Diff line
@@ -891,6 +891,89 @@ 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, 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

 *

include/linux/writeback.h

+2 −0
Original line number Diff line number Diff line
@@ -217,6 +217,8 @@ 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);

void cgroup_writeback_umount(void);



/**