address_space->writeback_index keeps track of where to write next for
cyclic writebacks. When cgroup writeback is used, an adress_space can
be written back by multiple wb's (bdi_writeback's) and sharing the
cyclic cursor across them doesn't make sense.
This patch adds inode_cgwb_link->writeback_index and introduces and
uses mapping_writeback_index_wbc() to determine the writeback cursor
to use. If the writeback_control in effect indicates that non-root
cgroup writeback is in progress, the matching inode_cgwb_link's
writeback_index is used; otherwise, the mapping one is used.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
---
include/linux/backing-dev-defs.h | 2 ++
include/linux/backing-dev.h | 30 ++++++++++++++++++++++++++++++
mm/page-writeback.c | 5 +++--
3 files changed, 35 insertions(+), 2 deletions(-)
diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index e3b18f3..6d64a0e 100644
--- a/include/linux/backing-dev-defs.h
+++ b/include/linux/backing-dev-defs.h
@@ -193,6 +193,8 @@ struct inode_cgwb_link {
struct hlist_node inode_node; /* RCU-safe, sorted */
struct list_head wb_node;
+ pgoff_t writeback_index; /* cyclic writeback cursor */
+
struct rcu_head rcu;
};
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 5a163fa..57dd200 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -551,6 +551,30 @@ bdi_writeback_wb(struct backing_dev_info *bdi, struct writeback_control *wbc)
}
/**
+ * mapping_writeback_index - determine the cursor for cyclic writeback
+ * @mapping: address_space under writeback
+ * @wbc: writeback_control in effect
+ *
+ * Called from address_space_operations->writepages() implementations to
+ * retrieve the pointer to the cursor variable to use for cyclic
+ * writebacks. If cgroup writeback is enabled, there's a separate cyclic
+ * cursor for each cgroup writing back @mapping.
+ */
+static inline pgoff_t *mapping_writeback_index(struct address_space *mapping,
+ struct writeback_control *wbc)
+{
+ struct inode_wb_link *iwbl = wbc->iwbl;
+
+ if (!iwbl || iwbl_to_wb(iwbl)->blkcg_css == blkcg_root_css) {
+ return &mapping->writeback_index;
+ } else {
+ struct inode_cgwb_link *icgwbl =
+ container_of(iwbl, struct inode_cgwb_link, iwbl);
+ return &icgwbl->writeback_index;
+ }
+}
+
+/**
* wbc_blkcg_css - return the blkcg_css associated with a wbc
* @wbc: writeback_control of interest
*
@@ -652,6 +676,12 @@ bdi_writeback_wb(struct backing_dev_info *bdi, struct writeback_control *wbc)
return &bdi->wb;
}
+static inline pgoff_t *mapping_writeback_index(struct address_space *mapping,
+ struct writeback_control *wbc)
+{
+ return &mapping->writeback_index;
+}
+
static inline struct cgroup_subsys_state *
wbc_blkcg_css(struct writeback_control *wbc)
{
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 3e31458..753d76f 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1906,6 +1906,7 @@ int write_cache_pages(struct address_space *mapping,
int done = 0;
struct pagevec pvec;
int nr_pages;
+ pgoff_t *writeback_index_ptr = mapping_writeback_index(mapping, wbc);
pgoff_t uninitialized_var(writeback_index);
pgoff_t index;
pgoff_t end; /* Inclusive */
@@ -1916,7 +1917,7 @@ int write_cache_pages(struct address_space *mapping,
pagevec_init(&pvec, 0);
if (wbc->range_cyclic) {
- writeback_index = mapping->writeback_index; /* prev offset */
+ writeback_index = *writeback_index_ptr; /* prev offset */
index = writeback_index;
if (index == 0)
cycled = 1;
@@ -2048,7 +2049,7 @@ continue_unlock:
goto retry;
}
if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
- mapping->writeback_index = done_index;
+ *writeback_index_ptr = done_index;
return ret;
}
--
2.1.0
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