fs-writeback: Add helper function to start writeback if idle

ext4, at least, would like to start pushing on writeback if it starts to get close to ENOSPC when reserving worst-case blocks for delalloc writes. Writing out delalloc data will convert those worst-case predictions into usually smaller actual usage, freeing up space before we hit ENOSPC based on this speculation.

Thanks to Jens for the suggestion for the helper function, & the naming help.

I've made the helper return status on whether writeback was started even though I don't plan to use it in the ext4 patch; it seems like it would be potentially useful to test this in some cases.

Signed-off-by Eric Sandeen <[email protected]>

---

fs/fs-writeback.c +17 -0

index 9d5360c..bff5f77 100644
@@ -1213,6 +1213,23 @@ void writeback_inodes_sb(struct super_block *sb)
 EXPORT_SYMBOL(writeback_inodes_sb);
 
 /**
+ * writeback_inodes_sb_if_idle	-	start writeback if none underway
+ * @sb: the superblock
+ *
+ * Invoke writeback_inodes_sb if no writeback is currently underway.
+ * Returns 1 if writeback was started, 0 if not.
+ */
+int writeback_inodes_sb_if_idle(struct super_block *sb)
+{
+	if (!writeback_in_progress(sb->s_bdi)) {
+		writeback_inodes_sb(sb);
+		return 1;
+	} else
+		return 0;
+}
+EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
+
+/**
  * sync_inodes_sb	-	sync sb inode pages
  * @sb: the superblock
  *

include/linux/writeback.h +1 -1

index 66ebddc..dc52482 100644
@@ -69,6 +69,7 @@ struct writeback_control {
 struct bdi_writeback;
 int inode_wait(void *);
 void writeback_inodes_sb(struct super_block *);
+int writeback_inodes_sb_if_idle(struct super_block *);
 void sync_inodes_sb(struct super_block *);
 void writeback_inodes_wbc(struct writeback_control *wbc);
 long wb_do_writeback(struct bdi_writeback *wb, int force_wait);
 
--

To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html

ext4, at least, would like to start pushing on writeback if it starts to get close to ENOSPC when reserving worst-case blocks for delalloc writes. Writing out delalloc data will convert those worst-case predictions into usually smaller actual usage, freeing up space before we hit ENOSPC based on this speculation.

Thanks to Jens for the suggestion for the helper function, & the naming help.

I've made the helper return status on whether writeback was started even though I don't plan to use it in the ext4 patch; it seems like it would be potentially useful to test this in some cases.

Quoted 9 lines · Eric Sandeen

ext4, at least, would like to start pushing on writeback if it starts to get close to ENOSPC when reserving worst-case blocks for delalloc writes. Writing out delalloc data will convert those worst-case predictions into usually smaller actual usage, freeing up space before we hit ENOSPC based on this speculation.

Thanks to Jens for the suggestion for the helper function, & the naming help.

Quoted 4 lines

I've made the helper return status on whether writeback was started even though I don't plan to use it in the ext4 patch; it seems like it would be potentially useful to test this in some cases.

Eric, how do you want to merge these? I can easily take this first one through any branch, but I suppose the ext4 one should go through the proper ext4 channels.

Quoted 15 lines · Jens Axboe

Quoted 13 lines · Eric Sandeen

ext4, at least, would like to start pushing on writeback if it starts to get close to ENOSPC when reserving worst-case blocks for delalloc writes. Writing out delalloc data will convert those worst-case predictions into usually smaller actual usage, freeing up space before we hit ENOSPC based on this speculation.

Thanks to Jens for the suggestion for the helper function, & the naming help.

I've made the helper return status on whether writeback was started even though I don't plan to use it in the ext4 patch; it seems like it would be potentially useful to test this in some cases.

Quoted 3 lines

Eric, how do you want to merge these? I can easily take this first one through any branch, but I suppose the ext4 one should go through the proper ext4 channels.

Doesn't matter to me really; maybe it'd be simpler if it all went though the ext4 tree so that there aren't any ordering problems?

Quoted 2 lines

Doesn't matter to me really; maybe it'd be simpler if it all went though the ext4 tree so that there aren't any ordering problems?

Definately :-)