From c2a4f3183a1248f615a695fbd8905da55ad11bba Mon Sep 17 00:00:00 2001 From: Kent Overstreet Date: Mon, 23 Sep 2013 23:17:31 -0700 Subject: [PATCH] bcache: Fix a writeback performance regression Background writeback works by scanning the btree for dirty data and adding those keys into a fixed size buffer, then for each dirty key in the keybuf writing it to the backing device. When read_dirty() finishes and it's time to scan for more dirty data, we need to wait for the outstanding writeback IO to finish - they still take up slots in the keybuf (so that foreground writes can check for them to avoid races) - without that wait, we'll continually rescan when we'll be able to add at most a key or two to the keybuf, and that takes locks that starves foreground IO. Doh. Signed-off-by: Kent Overstreet Cc: linux-stable # >= v3.10 Signed-off-by: Linus Torvalds --- Reading git-format-patch failed