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From: Tejun Heo <tj@kernel.org>
To: axboe@kernel.dk, jack@suse.cz, hannes@cmpxchg.org,
	mhocko@kernel.org, vdavydov.dev@gmail.com
Cc: cgroups@vger.kernel.org, linux-mm@kvack.org,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	kernel-team@fb.com, guro@fb.com, akpm@linux-foundation.org
Subject: [PATCH 3/5] writeback: Separate out wb_get_lookup() from wb_get_create()
Date: Thu, 15 Aug 2019 12:58:23 -0700
Message-ID: <20190815195823.GD2263813@devbig004.ftw2.facebook.com> (raw)
In-Reply-To: <20190815195619.GA2263813@devbig004.ftw2.facebook.com>

Separate out wb_get_lookup() which doesn't try to create one if there
isn't already one from wb_get_create().  This will be used by later
patches.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
 include/linux/backing-dev.h |    2 +
 mm/backing-dev.c            |   55 +++++++++++++++++++++++++++++---------------
 2 files changed, 39 insertions(+), 18 deletions(-)

--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -230,6 +230,8 @@ static inline int bdi_sched_wait(void *w
 struct bdi_writeback_congested *
 wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp);
 void wb_congested_put(struct bdi_writeback_congested *congested);
+struct bdi_writeback *wb_get_lookup(struct backing_dev_info *bdi,
+				    struct cgroup_subsys_state *memcg_css);
 struct bdi_writeback *wb_get_create(struct backing_dev_info *bdi,
 				    struct cgroup_subsys_state *memcg_css,
 				    gfp_t gfp);
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -618,13 +618,12 @@ out_put:
 }
 
 /**
- * wb_get_create - get wb for a given memcg, create if necessary
+ * wb_get_lookup - get wb for a given memcg
  * @bdi: target bdi
  * @memcg_css: cgroup_subsys_state of the target memcg (must have positive ref)
- * @gfp: allocation mask to use
  *
- * Try to get the wb for @memcg_css on @bdi.  If it doesn't exist, try to
- * create one.  The returned wb has its refcount incremented.
+ * Try to get the wb for @memcg_css on @bdi.  The returned wb has its
+ * refcount incremented.
  *
  * This function uses css_get() on @memcg_css and thus expects its refcnt
  * to be positive on invocation.  IOW, rcu_read_lock() protection on
@@ -641,6 +640,39 @@ out_put:
  * each lookup.  On mismatch, the existing wb is discarded and a new one is
  * created.
  */
+struct bdi_writeback *wb_get_lookup(struct backing_dev_info *bdi,
+				    struct cgroup_subsys_state *memcg_css)
+{
+	struct bdi_writeback *wb;
+
+	if (!memcg_css->parent)
+		return &bdi->wb;
+
+	rcu_read_lock();
+	wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
+	if (wb) {
+		struct cgroup_subsys_state *blkcg_css;
+
+		/* see whether the blkcg association has changed */
+		blkcg_css = cgroup_get_e_css(memcg_css->cgroup, &io_cgrp_subsys);
+		if (unlikely(wb->blkcg_css != blkcg_css || !wb_tryget(wb)))
+			wb = NULL;
+		css_put(blkcg_css);
+	}
+	rcu_read_unlock();
+
+	return wb;
+}
+
+/**
+ * wb_get_create - get wb for a given memcg, create if necessary
+ * @bdi: target bdi
+ * @memcg_css: cgroup_subsys_state of the target memcg (must have positive ref)
+ * @gfp: allocation mask to use
+ *
+ * Try to get the wb for @memcg_css on @bdi.  If it doesn't exist, try to
+ * create one.  See wb_get_lookup() for more details.
+ */
 struct bdi_writeback *wb_get_create(struct backing_dev_info *bdi,
 				    struct cgroup_subsys_state *memcg_css,
 				    gfp_t gfp)
@@ -653,20 +685,7 @@ struct bdi_writeback *wb_get_create(stru
 		return &bdi->wb;
 
 	do {
-		rcu_read_lock();
-		wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
-		if (wb) {
-			struct cgroup_subsys_state *blkcg_css;
-
-			/* see whether the blkcg association has changed */
-			blkcg_css = cgroup_get_e_css(memcg_css->cgroup,
-						     &io_cgrp_subsys);
-			if (unlikely(wb->blkcg_css != blkcg_css ||
-				     !wb_tryget(wb)))
-				wb = NULL;
-			css_put(blkcg_css);
-		}
-		rcu_read_unlock();
+		wb = wb_get_lookup(bdi, memcg_css);
 	} while (!wb && !cgwb_create(bdi, memcg_css, gfp));
 
 	return wb;

  parent reply index

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-15 19:56 [PATCHSET v2] writeback, memcg: Implement foreign inode flushing Tejun Heo
2019-08-15 19:57 ` [PATCH 1/5] writeback: Generalize and expose wb_completion Tejun Heo
2019-08-15 19:57 ` [PATCH 2/5] bdi: Add bdi->id Tejun Heo
2019-08-15 19:58 ` Tejun Heo [this message]
2019-08-16 15:45   ` [PATCH 3/5] writeback: Separate out wb_get_lookup() from wb_get_create() Jan Kara
2019-08-15 19:59 ` [PATCH 4/5] writeback, memcg: Implement cgroup_writeback_by_id() Tejun Heo
2019-08-16 15:47   ` Jan Kara
2019-08-21 21:02   ` [PATCH v3 " Tejun Heo
2019-08-26 13:49     ` Jan Kara
2019-08-15 19:59 ` [PATCH 5/5] writeback, memcg: Implement foreign dirty flushing Tejun Heo
2019-08-16 16:02   ` Jan Kara
2019-08-21 16:00     ` Tejun Heo
2019-08-21 16:04       ` Tejun Heo
2019-08-21 21:02   ` [PATCH v3 " Tejun Heo
2019-08-26 13:54     ` Jan Kara
2019-08-26 15:58       ` Tejun Heo
2019-08-26 16:06 [PATCHSET v3] writeback, memcg: Implement foreign inode flushing Tejun Heo
2019-08-26 16:06 ` [PATCH 3/5] writeback: Separate out wb_get_lookup() from wb_get_create() Tejun Heo

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