blkcg: associate a blkg for pages being evicted by swap

A prior patch in this series added blkg association to bios issued by
cgroups. There are two other paths that we want to attribute work back
to the appropriate cgroup: swap and writeback. Here we modify the way
swap tags bios to include the blkg. Writeback will be tackle in the next
patch.

Signed-off-by: Dennis Zhou <dennisszhou@gmail.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bio.c

@@ -1956,30 +1956,6 @@ EXPORT_SYMBOL(bioset_init_from_src);
 
 #ifdef CONFIG_BLK_CGROUP
 
-#ifdef CONFIG_MEMCG
-/**
- * bio_associate_blkcg_from_page - associate a bio with the page's blkcg
- * @bio: target bio
- * @page: the page to lookup the blkcg from
- *
- * Associate @bio with the blkcg from @page's owning memcg.  This works like
- * every other associate function wrt references.
- */
-int bio_associate_blkcg_from_page(struct bio *bio, struct page *page)
-{
-	struct cgroup_subsys_state *blkcg_css;
-
-	if (unlikely(bio->bi_css))
-		return -EBUSY;
-	if (!page->mem_cgroup)
-		return 0;
-	blkcg_css = cgroup_get_e_css(page->mem_cgroup->css.cgroup,
-				     &io_cgrp_subsys);
-	bio->bi_css = blkcg_css;
-	return 0;
-}
-#endif /* CONFIG_MEMCG */
-
 /**
  * bio_associate_blkcg - associate a bio with the specified blkcg
  * @bio: target bio
@@ -2030,6 +2006,65 @@ int bio_associate_blkg(struct bio *bio, struct blkcg_gq *blkg)
 	return 0;
 }
 
+static int __bio_associate_blkg_from_css(struct bio *bio,
+					 struct cgroup_subsys_state *css)
+{
+	struct blkcg_gq *blkg;
+
+	rcu_read_lock();
+
+	blkg = blkg_lookup_create(css_to_blkcg(css), bio->bi_disk->queue);
+
+	rcu_read_unlock();
+
+	return bio_associate_blkg(bio, blkg);
+}
+
+/**
+ * bio_associate_blkg_from_css - associate a bio with a specified css
+ * @bio: target bio
+ * @css: target css
+ *
+ * Associate @bio with the blkg found by combining the css's blkg and the
+ * request_queue of the @bio.  This takes a reference on the css that will
+ * be put upon freeing of @bio.
+ */
+int bio_associate_blkg_from_css(struct bio *bio,
+				struct cgroup_subsys_state *css)
+{
+	css_get(css);
+	bio->bi_css = css;
+	return __bio_associate_blkg_from_css(bio, css);
+}
+EXPORT_SYMBOL_GPL(bio_associate_blkg_from_css);
+
+#ifdef CONFIG_MEMCG
+/**
+ * bio_associate_blkg_from_page - associate a bio with the page's blkg
+ * @bio: target bio
+ * @page: the page to lookup the blkcg from
+ *
+ * Associate @bio with the blkg from @page's owning memcg and the respective
+ * request_queue.  This works like every other associate function wrt
+ * references.
+ *
+ * Note: this must be called after bio has an associated device.
+ */
+int bio_associate_blkg_from_page(struct bio *bio, struct page *page)
+{
+	struct cgroup_subsys_state *css;
+
+	if (unlikely(bio->bi_css))
+		return -EBUSY;
+	if (!page->mem_cgroup)
+		return 0;
+	css = cgroup_get_e_css(page->mem_cgroup->css.cgroup, &io_cgrp_subsys);
+	bio->bi_css = css;
+
+	return __bio_associate_blkg_from_css(bio, css);
+}
+#endif /* CONFIG_MEMCG */
+
 /**
  * bio_associate_create_blkg - associate a bio with a blkg from q
  * @q: request_queue where bio is going

include/linux/bio.h

@@ -533,21 +533,26 @@ do {						\
 	disk_devt((bio)->bi_disk)
 
 #if defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
-int bio_associate_blkcg_from_page(struct bio *bio, struct page *page);
+int bio_associate_blkg_from_page(struct bio *bio, struct page *page);
 #else
-static inline int bio_associate_blkcg_from_page(struct bio *bio,
+static inline int bio_associate_blkg_from_page(struct bio *bio,
 					       struct page *page) { return 0; }
 #endif
 
 #ifdef CONFIG_BLK_CGROUP
 int bio_associate_blkcg(struct bio *bio, struct cgroup_subsys_state *blkcg_css);
 int bio_associate_blkg(struct bio *bio, struct blkcg_gq *blkg);
+int bio_associate_blkg_from_css(struct bio *bio,
+				struct cgroup_subsys_state *css);
 int bio_associate_create_blkg(struct request_queue *q, struct bio *bio);
 void bio_disassociate_task(struct bio *bio);
 void bio_clone_blkcg_association(struct bio *dst, struct bio *src);
 #else	/* CONFIG_BLK_CGROUP */
 static inline int bio_associate_blkcg(struct bio *bio,
 			struct cgroup_subsys_state *blkcg_css) { return 0; }
+static inline int bio_associate_blkg_from_css(struct bio *bio,
+					      struct cgroup_subsys_state *css)
+{ return 0; }
 static inline int bio_associate_create_blkg(struct request_queue *q,
 					    struct bio *bio) { return 0; }
 static inline void bio_disassociate_task(struct bio *bio) { }

mm/page_io.c

@@ -339,7 +339,7 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
 		goto out;
 	}
 	bio->bi_opf = REQ_OP_WRITE | REQ_SWAP | wbc_to_write_flags(wbc);
-	bio_associate_blkcg_from_page(bio, page);
+	bio_associate_blkg_from_page(bio, page);
 	count_swpout_vm_event(page);
 	set_page_writeback(page);
 	unlock_page(page);