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[PATCHSET cgroup/for-4.3] cgroup,memcg: generalize event handling and enable notifications on "memory.events"

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  [PATCHSET cgroup/for-4.3] cgroup,memcg: generalize event handling and enable notifications on "memory.events" Tejun Heo <tj@kernel.org> - 2015-08-11 20:00 +0200
    [PATCH 6/8] cgroup: restructure file creation / removal handling Tejun Heo <tj@kernel.org> - 2015-08-11 20:00 +0200
    [PATCH 5/8] cgroup: cosmetic updates to rebind_subsystems() Tejun Heo <tj@kernel.org> - 2015-08-11 20:00 +0200
    [PATCH 2/8] cgroup: replace cftype->mode with CFTYPE_WORLD_WRITABLE Tejun Heo <tj@kernel.org> - 2015-08-11 20:10 +0200
    [PATCH 1/8] cgroup: replace "cgroup.populated" with "cgroup.events" Tejun Heo <tj@kernel.org> - 2015-08-11 20:10 +0200
    Re: [PATCHSET cgroup/for-4.3] cgroup,memcg: generalize event  handling and enable notifications on "memory.events" Johannes Weiner <hannes@cmpxchg.org> - 2015-08-17 23:30 +0200
      Re: [PATCHSET cgroup/for-4.3] cgroup,memcg: generalize event  handling and enable notifications on "memory.events" Tejun Heo <tj@kernel.org> - 2015-08-17 23:40 +0200

#1205341 — [PATCHSET cgroup/for-4.3] cgroup,memcg: generalize event handling and enable notifications on "memory.events"

Hello,

This patchset establishes conventions on low frequency events,
converts "cgroup.populated" to "cgroup.events" accordingly,
generalizes event handling and enable notifications for
"memory.events".

This patchset contains the following eight patches.

 0001-cgroup-replace-cgroup.populated-with-cgroup.events.patch
 0002-cgroup-replace-cftype-mode-with-CFTYPE_WORLD_WRITABL.patch
 0003-cgroup-relocate-cgroup_populate_dir.patch
 0004-cgroup-make-cgroup_addrm_files-clean-up-after-itself.patch
 0005-cgroup-cosmetic-updates-to-rebind_subsystems.patch
 0006-cgroup-restructure-file-creation-removal-handling.patch
 0007-cgroup-generalize-obtaining-the-handles-of-and-notif.patch
 0008-memcg-generate-file-modified-notifications-on-memory.patch

0001 replaces "cgroup.populated" with "cgroup.events".  0002-0006 are
prep patches.  0007 generalizes event notification.  0008 hook up
event notifications for "memory.events".

This patchset is on top of cgroup/for-4.3 e753531991b8 ("Merge branch
'for-4.3-unified-base' into for-4.3") and available in the following
git branch.

 git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git review-events

diffstat follows.  Thanks.

 Documentation/cgroups/unified-hierarchy.txt |   15 +
 include/linux/cgroup-defs.h                 |   32 ++-
 include/linux/cgroup.h                      |   13 +
 kernel/cgroup.c                             |  264 ++++++++++++++--------------
 kernel/cpuset.c                             |    6 
 mm/memcontrol.c                             |    8 
 6 files changed, 194 insertions(+), 144 deletions(-)

--
tejun
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#1205342 — [PATCH 6/8] cgroup: restructure file creation / removal handling

The file creation / removal path has always been a bit icky and the
planned notification update requires css during file creation.
Restructure as follows.

* cgroup_addrm_files() now takes both @css and @cgrp and is only
  called directly by other file handling functions.

* cgroup_populate/clear_dir() are replaced with
  css_populate/clear_dir() taking @css and @cgrp_override.
  @cgrp_override is used only when files needs to be created on /
  removed from a cgroup which isn't attached to @css which happens
  during subsystem rebinds.  Subsystem loops are moved to the callers.

* cgroup_add_file() now takes both @css and @cgrp.  @css isn't used
  yet but will be used by the planned notification update.

This patch doens't cause any behavior changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
---
 kernel/cgroup.c | 143 ++++++++++++++++++++++++++++++--------------------------
 1 file changed, 76 insertions(+), 67 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 67d2ba3..b287522 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -200,7 +200,8 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss,
 		      bool visible);
 static void css_release(struct percpu_ref *ref);
 static void kill_css(struct cgroup_subsys_state *css);
-static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
+static int cgroup_addrm_files(struct cgroup_subsys_state *css,
+			      struct cgroup *cgrp, struct cftype cfts[],
 			      bool is_add);
 
 /* IDR wrappers which synchronize using cgroup_idr_lock */
@@ -1218,53 +1219,57 @@ static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
 }
 
 /**
- * cgroup_clear_dir - remove subsys files in a cgroup directory
- * @cgrp: target cgroup
- * @subsys_mask: mask of the subsystem ids whose files should be removed
+ * css_clear_dir - remove subsys files in a cgroup directory
+ * @css: taget css
+ * @cgrp_override: specify if target cgroup is different from css->cgroup
  */
-static void cgroup_clear_dir(struct cgroup *cgrp, unsigned long subsys_mask)
+static void css_clear_dir(struct cgroup_subsys_state *css,
+			  struct cgroup *cgrp_override)
 {
-	struct cgroup_subsys *ss;
-	int i;
+	struct cgroup *cgrp = cgrp_override ?: css->cgroup;
+	struct cftype *cfts;
 
-	for_each_subsys(ss, i) {
-		struct cftype *cfts;
-
-		if (!(subsys_mask & (1 << i)))
-			continue;
-		list_for_each_entry(cfts, &ss->cfts, node)
-			cgroup_addrm_files(cgrp, cfts, false);
-	}
+	list_for_each_entry(cfts, &css->ss->cfts, node)
+		cgroup_addrm_files(css, cgrp, cfts, false);
 }
 
 /**
- * cgroup_populate_dir - create subsys files in a cgroup directory
- * @cgrp: target cgroup
- * @subsys_mask: mask of the subsystem ids whose files should be added
+ * css_populate_dir - create subsys files in a cgroup directory
+ * @css: target css
+ * @cgrp_overried: specify if target cgroup is different from css->cgroup
  *
  * On failure, no file is added.
  */
-static int cgroup_populate_dir(struct cgroup *cgrp, unsigned long subsys_mask)
+static int css_populate_dir(struct cgroup_subsys_state *css,
+			    struct cgroup *cgrp_override)
 {
-	struct cgroup_subsys *ss;
-	int i, ret = 0;
+	struct cgroup *cgrp = cgrp_override ?: css->cgroup;
+	struct cftype *cfts, *failed_cfts;
+	int ret;
 
-	/* process cftsets of each subsystem */
-	for_each_subsys(ss, i) {
-		struct cftype *cfts;
+	if (!css->ss) {
+		if (cgroup_on_dfl(cgrp))
+			cfts = cgroup_dfl_base_files;
+		else
+			cfts = cgroup_legacy_base_files;
 
-		if (!(subsys_mask & (1 << i)))
-			continue;
+		return cgroup_addrm_files(&cgrp->self, cgrp, cfts, true);
+	}
 
-		list_for_each_entry(cfts, &ss->cfts, node) {
-			ret = cgroup_addrm_files(cgrp, cfts, true);
-			if (ret < 0)
-				goto err;
+	list_for_each_entry(cfts, &css->ss->cfts, node) {
+		ret = cgroup_addrm_files(css, cgrp, cfts, true);
+		if (ret < 0) {
+			failed_cfts = cfts;
+			goto err;
 		}
 	}
 	return 0;
 err:
-	cgroup_clear_dir(cgrp, subsys_mask);
+	list_for_each_entry(cfts, &css->ss->cfts, node) {
+		if (cfts == failed_cfts)
+			break;
+		cgroup_addrm_files(css, cgrp, cfts, false);
+	}
 	return ret;
 }
 
@@ -1293,10 +1298,13 @@ static int rebind_subsystems(struct cgroup_root *dst_root,
 	if (dst_root == &cgrp_dfl_root)
 		tmp_ss_mask &= ~cgrp_dfl_root_inhibit_ss_mask;
 
-	ret = cgroup_populate_dir(dcgrp, tmp_ss_mask);
-	if (ret) {
-		if (dst_root != &cgrp_dfl_root)
-			return ret;
+	for_each_subsys_which(ss, ssid, &tmp_ss_mask) {
+		struct cgroup *scgrp = &ss->root->cgrp;
+		int tssid;
+
+		ret = css_populate_dir(cgroup_css(scgrp, ss), dcgrp);
+		if (!ret)
+			continue;
 
 		/*
 		 * Rebinding back to the default root is not allowed to
@@ -1304,20 +1312,27 @@ static int rebind_subsystems(struct cgroup_root *dst_root,
 		 * be rare.  Moving subsystems back and forth even more so.
 		 * Just warn about it and continue.
 		 */
-		if (cgrp_dfl_root_visible) {
-			pr_warn("failed to create files (%d) while rebinding 0x%lx to default root\n",
-				ret, ss_mask);
-			pr_warn("you may retry by moving them to a different hierarchy and unbinding\n");
+		if (dst_root == &cgrp_dfl_root) {
+			if (cgrp_dfl_root_visible) {
+				pr_warn("failed to create files (%d) while rebinding 0x%lx to default root\n",
+					ret, ss_mask);
+				pr_warn("you may retry by moving them to a different hierarchy and unbinding\n");
+			}
+			continue;
 		}
+
+		for_each_subsys_which(ss, tssid, &tmp_ss_mask) {
+			if (tssid == ssid)
+				break;
+			css_clear_dir(cgroup_css(scgrp, ss), dcgrp);
+		}
+		return ret;
 	}
 
 	/*
 	 * Nothing can fail from this point on.  Remove files for the
 	 * removed subsystems and rebind each subsystem.
 	 */
-	for_each_subsys_which(ss, ssid, &ss_mask)
-		cgroup_clear_dir(&ss->root->cgrp, 1 << ssid);
-
 	for_each_subsys_which(ss, ssid, &ss_mask) {
 		struct cgroup_root *src_root = ss->root;
 		struct cgroup *scgrp = &src_root->cgrp;
@@ -1326,6 +1341,8 @@ static int rebind_subsystems(struct cgroup_root *dst_root,
 
 		WARN_ON(!css || cgroup_css(dcgrp, ss));
 
+		css_clear_dir(css, NULL);
+
 		RCU_INIT_POINTER(scgrp->subsys[ssid], NULL);
 		rcu_assign_pointer(dcgrp->subsys[ssid], css);
 		ss->root = dst_root;
@@ -1691,7 +1708,6 @@ static int cgroup_setup_root(struct cgroup_root *root, unsigned long ss_mask)
 {
 	LIST_HEAD(tmp_links);
 	struct cgroup *root_cgrp = &root->cgrp;
-	struct cftype *base_files;
 	struct css_set *cset;
 	int i, ret;
 
@@ -1730,12 +1746,7 @@ static int cgroup_setup_root(struct cgroup_root *root, unsigned long ss_mask)
 	}
 	root_cgrp->kn = root->kf_root->kn;
 
-	if (root == &cgrp_dfl_root)
-		base_files = cgroup_dfl_base_files;
-	else
-		base_files = cgroup_legacy_base_files;
-
-	ret = cgroup_addrm_files(root_cgrp, base_files, true);
+	ret = css_populate_dir(&root_cgrp->self, NULL);
 	if (ret)
 		goto destroy_root;
 
@@ -2884,7 +2895,8 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
 				ret = create_css(child, ss,
 					cgrp->subtree_control & (1 << ssid));
 			else
-				ret = cgroup_populate_dir(child, 1 << ssid);
+				ret = css_populate_dir(cgroup_css(child, ss),
+						       NULL);
 			if (ret)
 				goto err_undo_css;
 		}
@@ -2917,7 +2929,7 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
 			if (css_disable & (1 << ssid)) {
 				kill_css(css);
 			} else {
-				cgroup_clear_dir(child, 1 << ssid);
+				css_clear_dir(css, NULL);
 				if (ss->css_reset)
 					ss->css_reset(css);
 			}
@@ -2965,7 +2977,7 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
 			if (css_enable & (1 << ssid))
 				kill_css(css);
 			else
-				cgroup_clear_dir(child, 1 << ssid);
+				css_clear_dir(css, NULL);
 		}
 	}
 	goto out_unlock;
@@ -3117,7 +3129,8 @@ static int cgroup_kn_set_ugid(struct kernfs_node *kn)
 	return kernfs_setattr(kn, &iattr);
 }
 
-static int cgroup_add_file(struct cgroup *cgrp, struct cftype *cft)
+static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
+			   struct cftype *cft)
 {
 	char name[CGROUP_FILE_NAME_MAX];
 	struct kernfs_node *kn;
@@ -3148,14 +3161,16 @@ static int cgroup_add_file(struct cgroup *cgrp, struct cftype *cft)
 
 /**
  * cgroup_addrm_files - add or remove files to a cgroup directory
- * @cgrp: the target cgroup
+ * @css: the target css
+ * @cgrp: the target cgroup (usually css->cgroup)
  * @cfts: array of cftypes to be added
  * @is_add: whether to add or remove
  *
  * Depending on @is_add, add or remove files defined by @cfts on @cgrp.
  * For removals, this function never fails.
  */
-static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
+static int cgroup_addrm_files(struct cgroup_subsys_state *css,
+			      struct cgroup *cgrp, struct cftype cfts[],
 			      bool is_add)
 {
 	struct cftype *cft, *cft_end = NULL;
@@ -3176,7 +3191,7 @@ static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
 			continue;
 
 		if (is_add) {
-			ret = cgroup_add_file(cgrp, cft);
+			ret = cgroup_add_file(css, cgrp, cft);
 			if (ret) {
 				pr_warn("%s: failed to add %s, err=%d\n",
 					__func__, cft->name, ret);
@@ -3208,7 +3223,7 @@ static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
 		if (cgroup_is_dead(cgrp))
 			continue;
 
-		ret = cgroup_addrm_files(cgrp, cfts, is_add);
+		ret = cgroup_addrm_files(css, cgrp, cfts, is_add);
 		if (ret)
 			break;
 	}
@@ -4584,7 +4599,7 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss,
 	css->id = err;
 
 	if (visible) {
-		err = cgroup_populate_dir(cgrp, 1 << ss->id);
+		err = css_populate_dir(css, NULL);
 		if (err)
 			goto err_free_id;
 	}
@@ -4610,7 +4625,7 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss,
 
 err_list_del:
 	list_del_rcu(&css->sibling);
-	cgroup_clear_dir(css->cgroup, 1 << css->ss->id);
+	css_clear_dir(css, NULL);
 err_free_id:
 	cgroup_idr_remove(&ss->css_idr, css->id);
 err_free_percpu_ref:
@@ -4627,7 +4642,6 @@ static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
 	struct cgroup_root *root;
 	struct cgroup_subsys *ss;
 	struct kernfs_node *kn;
-	struct cftype *base_files;
 	int ssid, ret;
 
 	/* Do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable.
@@ -4703,12 +4717,7 @@ static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
 	if (ret)
 		goto out_destroy;
 
-	if (cgroup_on_dfl(cgrp))
-		base_files = cgroup_dfl_base_files;
-	else
-		base_files = cgroup_legacy_base_files;
-
-	ret = cgroup_addrm_files(cgrp, base_files, true);
+	ret = css_populate_dir(&cgrp->self, NULL);
 	if (ret)
 		goto out_destroy;
 
@@ -4795,7 +4804,7 @@ static void kill_css(struct cgroup_subsys_state *css)
 	 * This must happen before css is disassociated with its cgroup.
 	 * See seq_css() for details.
 	 */
-	cgroup_clear_dir(css->cgroup, 1 << css->ss->id);
+	css_clear_dir(css, NULL);
 
 	/*
 	 * Killing would put the base ref, but we need to keep it alive
-- 
2.4.3

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#1205343 — [PATCH 5/8] cgroup: cosmetic updates to rebind_subsystems()

* Use local variables @scgrp and @dcgrp for @src_root->cgrp and
  @dst_root->cgrp respectively.

* Use initializers to set @src_root and @css in the inner bind loop.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
---
 kernel/cgroup.c | 31 +++++++++++++++----------------
 1 file changed, 15 insertions(+), 16 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 5e5a4e0..67d2ba3 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1271,6 +1271,7 @@ static int cgroup_populate_dir(struct cgroup *cgrp, unsigned long subsys_mask)
 static int rebind_subsystems(struct cgroup_root *dst_root,
 			     unsigned long ss_mask)
 {
+	struct cgroup *dcgrp = &dst_root->cgrp;
 	struct cgroup_subsys *ss;
 	unsigned long tmp_ss_mask;
 	int ssid, i, ret;
@@ -1292,7 +1293,7 @@ static int rebind_subsystems(struct cgroup_root *dst_root,
 	if (dst_root == &cgrp_dfl_root)
 		tmp_ss_mask &= ~cgrp_dfl_root_inhibit_ss_mask;
 
-	ret = cgroup_populate_dir(&dst_root->cgrp, tmp_ss_mask);
+	ret = cgroup_populate_dir(dcgrp, tmp_ss_mask);
 	if (ret) {
 		if (dst_root != &cgrp_dfl_root)
 			return ret;
@@ -1318,42 +1319,40 @@ static int rebind_subsystems(struct cgroup_root *dst_root,
 		cgroup_clear_dir(&ss->root->cgrp, 1 << ssid);
 
 	for_each_subsys_which(ss, ssid, &ss_mask) {
-		struct cgroup_root *src_root;
-		struct cgroup_subsys_state *css;
+		struct cgroup_root *src_root = ss->root;
+		struct cgroup *scgrp = &src_root->cgrp;
+		struct cgroup_subsys_state *css = cgroup_css(scgrp, ss);
 		struct css_set *cset;
 
-		src_root = ss->root;
-		css = cgroup_css(&src_root->cgrp, ss);
-
-		WARN_ON(!css || cgroup_css(&dst_root->cgrp, ss));
+		WARN_ON(!css || cgroup_css(dcgrp, ss));
 
-		RCU_INIT_POINTER(src_root->cgrp.subsys[ssid], NULL);
-		rcu_assign_pointer(dst_root->cgrp.subsys[ssid], css);
+		RCU_INIT_POINTER(scgrp->subsys[ssid], NULL);
+		rcu_assign_pointer(dcgrp->subsys[ssid], css);
 		ss->root = dst_root;
-		css->cgroup = &dst_root->cgrp;
+		css->cgroup = dcgrp;
 
 		down_write(&css_set_rwsem);
 		hash_for_each(css_set_table, i, cset, hlist)
 			list_move_tail(&cset->e_cset_node[ss->id],
-				       &dst_root->cgrp.e_csets[ss->id]);
+				       &dcgrp->e_csets[ss->id]);
 		up_write(&css_set_rwsem);
 
 		src_root->subsys_mask &= ~(1 << ssid);
-		src_root->cgrp.subtree_control &= ~(1 << ssid);
-		cgroup_refresh_child_subsys_mask(&src_root->cgrp);
+		scgrp->subtree_control &= ~(1 << ssid);
+		cgroup_refresh_child_subsys_mask(scgrp);
 
 		/* default hierarchy doesn't enable controllers by default */
 		dst_root->subsys_mask |= 1 << ssid;
 		if (dst_root != &cgrp_dfl_root) {
-			dst_root->cgrp.subtree_control |= 1 << ssid;
-			cgroup_refresh_child_subsys_mask(&dst_root->cgrp);
+			dcgrp->subtree_control |= 1 << ssid;
+			cgroup_refresh_child_subsys_mask(dcgrp);
 		}
 
 		if (ss->bind)
 			ss->bind(css);
 	}
 
-	kernfs_activate(dst_root->cgrp.kn);
+	kernfs_activate(dcgrp->kn);
 	return 0;
 }
 
-- 
2.4.3

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#1205348 — [PATCH 2/8] cgroup: replace cftype->mode with CFTYPE_WORLD_WRITABLE

cftype->mode allows controllers to give arbitrary permissions to
interface knobs.  Except for "cgroup.event_control", the existing uses
are spurious.

* Some explicitly specify S_IRUGO | S_IWUSR even though that's the
  default.

* "cpuset.memory_pressure" specifies S_IRUGO while also setting a
  write callback which returns -EACCES.  All it needs to do is simply
  not setting a write callback.

"cgroup.event_control" uses cftype->mode to make the file
world-writable.  It's a misdesigned interface and we don't want
controllers to be tweaking interface file permissions in general.
This patch removes cftype->mode and all its spurious uses and
implements CFTYPE_WORLD_WRITABLE for "cgroup.event_control" which is
marked as compatibility-only.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/cgroup-defs.h |  6 +-----
 kernel/cgroup.c             | 19 +++++++------------
 kernel/cpuset.c             |  6 ------
 mm/memcontrol.c             |  3 +--
 4 files changed, 9 insertions(+), 25 deletions(-)

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 74d241d..93f48ca 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -76,6 +76,7 @@ enum {
 	CFTYPE_ONLY_ON_ROOT	= (1 << 0),	/* only create on root cgrp */
 	CFTYPE_NOT_ON_ROOT	= (1 << 1),	/* don't create on root cgrp */
 	CFTYPE_NO_PREFIX	= (1 << 3),	/* (DON'T USE FOR NEW FILES) no subsys prefix */
+	CFTYPE_WORLD_WRITABLE	= (1 << 4),	/* (DON'T USE FOR NEW FILES) S_IWUGO */
 
 	/* internal flags, do not use outside cgroup core proper */
 	__CFTYPE_ONLY_ON_DFL	= (1 << 16),	/* only on default hierarchy */
@@ -324,11 +325,6 @@ struct cftype {
 	 */
 	char name[MAX_CFTYPE_NAME];
 	unsigned long private;
-	/*
-	 * If not 0, file mode is set to this value, otherwise it will
-	 * be figured out automatically
-	 */
-	umode_t mode;
 
 	/*
 	 * The maximum length of string, excluding trailing nul, that can
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 43535fc..a909e4d 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1044,23 +1044,21 @@ static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
  * cgroup_file_mode - deduce file mode of a control file
  * @cft: the control file in question
  *
- * returns cft->mode if ->mode is not 0
- * returns S_IRUGO|S_IWUSR if it has both a read and a write handler
- * returns S_IRUGO if it has only a read handler
- * returns S_IWUSR if it has only a write hander
+ * S_IRUGO for read, S_IWUSR for write.
  */
 static umode_t cgroup_file_mode(const struct cftype *cft)
 {
 	umode_t mode = 0;
 
-	if (cft->mode)
-		return cft->mode;
-
 	if (cft->read_u64 || cft->read_s64 || cft->seq_show)
 		mode |= S_IRUGO;
 
-	if (cft->write_u64 || cft->write_s64 || cft->write)
-		mode |= S_IWUSR;
+	if (cft->write_u64 || cft->write_s64 || cft->write) {
+		if (cft->flags & CFTYPE_WORLD_WRITABLE)
+			mode |= S_IWUGO;
+		else
+			mode |= S_IWUSR;
+	}
 
 	return mode;
 }
@@ -4270,7 +4268,6 @@ static struct cftype cgroup_dfl_base_files[] = {
 		.seq_show = cgroup_pidlist_show,
 		.private = CGROUP_FILE_PROCS,
 		.write = cgroup_procs_write,
-		.mode = S_IRUGO | S_IWUSR,
 	},
 	{
 		.name = "cgroup.controllers",
@@ -4305,7 +4302,6 @@ static struct cftype cgroup_legacy_base_files[] = {
 		.seq_show = cgroup_pidlist_show,
 		.private = CGROUP_FILE_PROCS,
 		.write = cgroup_procs_write,
-		.mode = S_IRUGO | S_IWUSR,
 	},
 	{
 		.name = "cgroup.clone_children",
@@ -4325,7 +4321,6 @@ static struct cftype cgroup_legacy_base_files[] = {
 		.seq_show = cgroup_pidlist_show,
 		.private = CGROUP_FILE_TASKS,
 		.write = cgroup_tasks_write,
-		.mode = S_IRUGO | S_IWUSR,
 	},
 	{
 		.name = "notify_on_release",
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index ee14e3a..4da3f45 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1594,9 +1594,6 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft,
 	case FILE_MEMORY_PRESSURE_ENABLED:
 		cpuset_memory_pressure_enabled = !!val;
 		break;
-	case FILE_MEMORY_PRESSURE:
-		retval = -EACCES;
-		break;
 	case FILE_SPREAD_PAGE:
 		retval = update_flag(CS_SPREAD_PAGE, cs, val);
 		break;
@@ -1863,9 +1860,6 @@ static struct cftype files[] = {
 	{
 		.name = "memory_pressure",
 		.read_u64 = cpuset_read_u64,
-		.write_u64 = cpuset_write_u64,
-		.private = FILE_MEMORY_PRESSURE,
-		.mode = S_IRUGO,
 	},
 
 	{
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index acb93c5..78ba418 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4360,8 +4360,7 @@ static struct cftype mem_cgroup_legacy_files[] = {
 	{
 		.name = "cgroup.event_control",		/* XXX: for compat */
 		.write = memcg_write_event_control,
-		.flags = CFTYPE_NO_PREFIX,
-		.mode = S_IWUGO,
+		.flags = CFTYPE_NO_PREFIX | CFTYPE_WORLD_WRITABLE,
 	},
 	{
 		.name = "swappiness",
-- 
2.4.3

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#1205351 — [PATCH 1/8] cgroup: replace "cgroup.populated" with "cgroup.events"

memcg already uses "memory.events" for event reporting and other
controllers may need event reporting too.  Let's standardize on
"$SUBSYS.events" interface file for reporting events which don't
happen too frequently and thus can share event notification.

"cgroup.populated" is replaced with "populated" field in
"cgroup.events" and documentation is updated accordingly.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
---
 Documentation/cgroups/unified-hierarchy.txt | 15 ++++++++++-----
 include/linux/cgroup-defs.h                 |  2 +-
 kernel/cgroup.c                             | 17 +++++++++--------
 3 files changed, 20 insertions(+), 14 deletions(-)

diff --git a/Documentation/cgroups/unified-hierarchy.txt b/Documentation/cgroups/unified-hierarchy.txt
index 1ee9caf..7ea2bc1 100644
--- a/Documentation/cgroups/unified-hierarchy.txt
+++ b/Documentation/cgroups/unified-hierarchy.txt
@@ -341,11 +341,11 @@ is riddled with issues.
   unnecessarily complicated and probably done this way because event
   delivery itself was expensive.
 
-Unified hierarchy implements an interface file "cgroup.populated"
-which can be used to monitor whether the cgroup's subhierarchy has
-tasks in it or not.  Its value is 0 if there is no task in the cgroup
-and its descendants; otherwise, 1.  poll and [id]notify events are
-triggered when the value changes.
+Unified hierarchy implements "populated" field in "cgroup.events"
+interface file which can be used to monitor whether the cgroup's
+subhierarchy has tasks in it or not.  Its value is 0 if there is no
+task in the cgroup and its descendants; otherwise, 1.  poll and
+[id]notify events are triggered when the value changes.
 
 This is significantly lighter and simpler and trivially allows
 delegating management of subhierarchy - subhierarchy monitoring can
@@ -435,6 +435,11 @@ may be specified in any order and not all pairs have to be specified.
   the first entry in the file.  Specific entries can use "default" as
   its value to indicate inheritance of the default value.
 
+- For events which are not very high frequency, an interface file
+  "events" should be created which lists event key value pairs.
+  Whenever a notifiable event happens, file modified event should be
+  generated on the file.
+
 
 5-4. Per-Controller Changes
 
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 5294f1f..74d241d 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -226,7 +226,7 @@ struct cgroup {
 
 	struct kernfs_node *kn;		/* cgroup kernfs entry */
 	struct kernfs_node *procs_kn;	/* kn for "cgroup.procs" */
-	struct kernfs_node *populated_kn; /* kn for "cgroup.subtree_populated" */
+	struct kernfs_node *events_kn;	/* kn for "cgroup.events" */
 
 	/*
 	 * The bitmask of subsystems enabled on the child cgroups.
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index c4d94a5..43535fc 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -519,8 +519,8 @@ static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
 		if (!trigger)
 			break;
 
-		if (cgrp->populated_kn)
-			kernfs_notify(cgrp->populated_kn);
+		if (cgrp->events_kn)
+			kernfs_notify(cgrp->events_kn);
 		cgrp = cgroup_parent(cgrp);
 	} while (cgrp);
 }
@@ -2944,9 +2944,10 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
 	goto out_unlock;
 }
 
-static int cgroup_populated_show(struct seq_file *seq, void *v)
+static int cgroup_events_show(struct seq_file *seq, void *v)
 {
-	seq_printf(seq, "%d\n", (bool)seq_css(seq)->cgroup->populated_cnt);
+	seq_printf(seq, "populated %d\n",
+		   (bool)seq_css(seq)->cgroup->populated_cnt);
 	return 0;
 }
 
@@ -3113,8 +3114,8 @@ static int cgroup_add_file(struct cgroup *cgrp, struct cftype *cft)
 
 	if (cft->write == cgroup_procs_write)
 		cgrp->procs_kn = kn;
-	else if (cft->seq_show == cgroup_populated_show)
-		cgrp->populated_kn = kn;
+	else if (cft->seq_show == cgroup_events_show)
+		cgrp->events_kn = kn;
 	return 0;
 }
 
@@ -4287,9 +4288,9 @@ static struct cftype cgroup_dfl_base_files[] = {
 		.write = cgroup_subtree_control_write,
 	},
 	{
-		.name = "cgroup.populated",
+		.name = "cgroup.events",
 		.flags = CFTYPE_NOT_ON_ROOT,
-		.seq_show = cgroup_populated_show,
+		.seq_show = cgroup_events_show,
 	},
 	{ }	/* terminate */
 };
-- 
2.4.3

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#1208898 — Re: [PATCHSET cgroup/for-4.3] cgroup,memcg: generalize event handling and enable notifications on "memory.events"

On Tue, Aug 11, 2015 at 01:58:01PM -0400, Tejun Heo wrote:
> Hello,
> 
> This patchset establishes conventions on low frequency events,
> converts "cgroup.populated" to "cgroup.events" accordingly,
> generalizes event handling and enable notifications for
> "memory.events".
> 
> This patchset contains the following eight patches.
> 
>  0001-cgroup-replace-cgroup.populated-with-cgroup.events.patch
>  0002-cgroup-replace-cftype-mode-with-CFTYPE_WORLD_WRITABL.patch
>  0003-cgroup-relocate-cgroup_populate_dir.patch
>  0004-cgroup-make-cgroup_addrm_files-clean-up-after-itself.patch
>  0005-cgroup-cosmetic-updates-to-rebind_subsystems.patch
>  0006-cgroup-restructure-file-creation-removal-handling.patch
>  0007-cgroup-generalize-obtaining-the-handles-of-and-notif.patch
>  0008-memcg-generate-file-modified-notifications-on-memory.patch
> 
> 0001 replaces "cgroup.populated" with "cgroup.events".  0002-0006 are
> prep patches.  0007 generalizes event notification.  0008 hook up
> event notifications for "memory.events".

These look good to me.

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Out of curiosity, do you envision additional entries for cgroup.events
in the near future?
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#1208903 — Re: [PATCHSET cgroup/for-4.3] cgroup,memcg: generalize event handling and enable notifications on "memory.events"

Hello,

On Mon, Aug 17, 2015 at 11:29:20PM +0200, Johannes Weiner wrote:
> Out of curiosity, do you envision additional entries for cgroup.events
> in the near future?

I don't have anything specific I can think of right now.  I primarily
want to establish interface convention regarding low-frequency event
delivery and memory.events's seemed simple and extensible.

Thanks.

-- 
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