Commit f817de98 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: prepare migration path for unified hierarchy 



Unified hierarchy implementation would require re-migrating tasks onto
the same cgroup on the default hierarchy to reflect updated effective
csses.  Update cgroup_migrate_prepare_dst() so that it accepts NULL as
the destination cgrp.  When NULL is specified, the destination is
considered to be the cgroup on the default hierarchy associated with
each css_set.

After this change, the identity check in cgroup_migrate_add_src()
isn't sufficient for noop detection as the associated csses may change
without any cgroup association changing.  The only way to tell whether
a migration is noop or not is testing whether the source and
destination csets are identical.  The noop check in
cgroup_migrate_add_src() is removed and cset identity test is added to
cgroup_migreate_prepare_dst().  If it's detected that source and
destination csets are identical, the cset is removed removed from
@preloaded_csets and all the migration nodes are cleared which makes
cgroup_migrate() ignore the cset.

Also, make the function append the destination css_sets to
@preloaded_list so that destination css_sets always come after source
css_sets.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 7fd8c565

kernel/cgroup.c

+23 −11
Original line number Diff line number Diff line
@@ -1902,10 +1902,6 @@ static void cgroup_migrate_add_src(struct css_set *src_cset, 


	src_cgrp = cset_cgroup_from_root(src_cset, dst_cgrp->root);



	/* nothing to do if this cset already belongs to the cgroup */

	if (src_cgrp == dst_cgrp)

		return;



	if (!list_empty(&src_cset->mg_preload_node))

		return;
@@ -1920,13 +1916,14 @@ static void cgroup_migrate_add_src(struct css_set *src_cset, 


/**

 * cgroup_migrate_prepare_dst - prepare destination css_sets for migration

 * @dst_cgrp: the destination cgroup

 * @dst_cgrp: the destination cgroup (may be %NULL)

 * @preloaded_csets: list of preloaded source css_sets

 *

 * Tasks are about to be moved to @dst_cgrp and all the source css_sets

 * have been preloaded to @preloaded_csets.  This function looks up and

 * pins all destination css_sets, links each to its source, and put them on

 * @preloaded_csets.

 * pins all destination css_sets, links each to its source, and append them

 * to @preloaded_csets.  If @dst_cgrp is %NULL, the destination of each

 * source css_set is assumed to be its cgroup on the default hierarchy.

 *

 * This function must be called after cgroup_migrate_add_src() has been

 * called on each migration source css_set.  After migration is performed
@@ -1937,19 +1934,34 @@ static int cgroup_migrate_prepare_dst(struct cgroup *dst_cgrp, 
				      struct list_head *preloaded_csets)

{

	LIST_HEAD(csets);

	struct css_set *src_cset;

	struct css_set *src_cset, *tmp_cset;



	lockdep_assert_held(&cgroup_mutex);



	/* look up the dst cset for each src cset and link it to src */

	list_for_each_entry(src_cset, preloaded_csets, mg_preload_node) {

	list_for_each_entry_safe(src_cset, tmp_cset, preloaded_csets, mg_preload_node) {

		struct css_set *dst_cset;



		dst_cset = find_css_set(src_cset, dst_cgrp);

		dst_cset = find_css_set(src_cset,

					dst_cgrp ?: src_cset->dfl_cgrp);

		if (!dst_cset)

			goto err;



		WARN_ON_ONCE(src_cset->mg_dst_cset || dst_cset->mg_dst_cset);



		/*

		 * If src cset equals dst, it's noop.  Drop the src.

		 * cgroup_migrate() will skip the cset too.  Note that we

		 * can't handle src == dst as some nodes are used by both.

		 */

		if (src_cset == dst_cset) {

			src_cset->mg_src_cgrp = NULL;

			list_del_init(&src_cset->mg_preload_node);

			put_css_set(src_cset, false);

			put_css_set(dst_cset, false);

			continue;

		}



		src_cset->mg_dst_cset = dst_cset;



		if (list_empty(&dst_cset->mg_preload_node))
@@ -1958,7 +1970,7 @@ static int cgroup_migrate_prepare_dst(struct cgroup *dst_cgrp, 
			put_css_set(dst_cset, false);

	}



	list_splice(&csets, preloaded_csets);

	list_splice_tail(&csets, preloaded_csets);

	return 0;

err:

	cgroup_migrate_finish(&csets);

CRA Git | Maintained and supported by SUSTech CRA and CCSE