writeback: make __writeback_single_inode() cgroup writeback aware
Metadata is always dirtied against the root cgroup and should thus be
written out only by the root cgroup writeback. This patch updates
__writeback_single_inode() so that it skips writing out metadata if
the writeback is for a non-root cgroup. wbc_skip_metadata() is added
to decide whether to skip metadata writeback.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index dbfd0b0..2bb14d5 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -684,6 +684,19 @@
return test_bit(IWBL_DIRTY_PAGES, &iwbl->data);
}
+/**
+ * wbc_skip_metadata - determine whether to skip writing out metadata
+ * @wbc: writeback_control in effect
+ *
+ * Called by __writeback_single_inode() to decide whether to skip writing
+ * out metadata. Metadata is always dirtied against the root cgroup and
+ * should only be written out by the root.
+ */
+static inline bool wbc_skip_metadata(struct writeback_control *wbc)
+{
+ return wbc->iwbl && !iwbl_is_root(wbc->iwbl);
+}
+
#else /* CONFIG_CGROUP_WRITEBACK */
static void init_cgwb_dirty_page_context(struct dirty_context *dctx)
@@ -791,6 +804,11 @@
return mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY);
}
+static inline bool wbc_skip_metadata(struct writeback_control *wbc)
+{
+ return false;
+}
+
#endif /* CONFIG_CGROUP_WRITEBACK */
/**
@@ -1128,6 +1146,7 @@
struct address_space *mapping = inode->i_mapping;
struct inode_wb_link *iwbl = inode_writeback_iwbl(inode, wbc);
long nr_to_write = wbc->nr_to_write;
+ bool skip_metadata = wbc_skip_metadata(wbc);
unsigned dirty;
int ret;
@@ -1144,7 +1163,7 @@
* separate, external IO completion path and ->sync_fs for guaranteeing
* inode metadata is written back correctly.
*/
- if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) {
+ if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync && !skip_metadata) {
int err = filemap_fdatawait(mapping);
if (ret == 0)
ret = err;
@@ -1157,8 +1176,12 @@
*/
spin_lock(&inode->i_lock);
- dirty = inode->i_state & I_DIRTY;
- inode->i_state &= ~I_DIRTY;
+ if (skip_metadata)
+ dirty = inode->i_state & I_DIRTY_PAGES;
+ else
+ dirty = inode->i_state & I_DIRTY;
+
+ inode->i_state &= ~dirty;
/*
* Paired with smp_mb() in __mark_inode_dirty_dctx(). This allows
