From bb0822954aab7d23a3f902c2a103ee0242f6046e Mon Sep 17 00:00:00 2001 From: Wu Fengguang Date: Tue, 16 Aug 2011 13:37:14 -0600 Subject: squeeze max-pause area and drop pass-good area Revert the pass-good area introduced in ffd1f609ab10 ("writeback: introduce max-pause and pass-good dirty limits") and make the max-pause area smaller and safe. This fixes ~30% performance regression in the ext3 data=writeback fio_mmap_randwrite_64k/fio_mmap_randrw_64k test cases, where there are 12 JBOD disks, on each disk runs 8 concurrent tasks doing reads+writes. Using deadline scheduler also has a regression, but not that big as CFQ, so this suggests we have some write starvation. The test logs show that - the disks are sometimes under utilized - global dirty pages sometimes rush high to the pass-good area for several hundred seconds, while in the mean time some bdi dirty pages drop to very low value (bdi_dirty << bdi_thresh). Then suddenly the global dirty pages dropped under global dirty threshold and bdi_dirty rush very high (for example, 2 times higher than bdi_thresh). During which time balance_dirty_pages() is not called at all. So the problems are 1) The random writes progress so slow that they break the assumption of the max-pause logic that "8 pages per 200ms is typically more than enough to curb heavy dirtiers". 2) The max-pause logic ignored task_bdi_thresh and thus opens the possibility for some bdi's to over dirty pages, leading to (bdi_dirty >> bdi_thresh) and then (bdi_thresh >> bdi_dirty) for others. 3) The higher max-pause/pass-good thresholds somehow leads to the bad swing of dirty pages. The fix is to allow the task to slightly dirty over task_bdi_thresh, but no way to exceed bdi_dirty and/or global dirty_thresh. Tests show that it fixed the JBOD regression completely (both behavior and performance), while still being able to cut down large pause times in balance_dirty_pages() for single-disk cases. Reported-by: Li Shaohua Tested-by: Li Shaohua Acked-by: Jan Kara Signed-off-by: Wu Fengguang --- include/linux/writeback.h | 11 ----------- 1 file changed, 11 deletions(-) (limited to 'include/linux/writeback.h') diff --git a/include/linux/writeback.h b/include/linux/writeback.h index f1bfa12ea246..2b8963ff0f35 100644 --- a/include/linux/writeback.h +++ b/include/linux/writeback.h @@ -12,15 +12,6 @@ * * (thresh - thresh/DIRTY_FULL_SCOPE, thresh) * - * The 1/16 region above the global dirty limit will be put to maximum pauses: - * - * (limit, limit + limit/DIRTY_MAXPAUSE_AREA) - * - * The 1/16 region above the max-pause region, dirty exceeded bdi's will be put - * to loops: - * - * (limit + limit/DIRTY_MAXPAUSE_AREA, limit + limit/DIRTY_PASSGOOD_AREA) - * * Further beyond, all dirtier tasks will enter a loop waiting (possibly long * time) for the dirty pages to drop, unless written enough pages. * @@ -31,8 +22,6 @@ */ #define DIRTY_SCOPE 8 #define DIRTY_FULL_SCOPE (DIRTY_SCOPE / 2) -#define DIRTY_MAXPAUSE_AREA 16 -#define DIRTY_PASSGOOD_AREA 8 /* * 4MB minimal write chunk size -- cgit v1.2.3 From af6a311384bce6c88e15c80ab22ab051a918b4eb Mon Sep 17 00:00:00 2001 From: Wu Fengguang Date: Mon, 3 Oct 2011 20:46:17 -0600 Subject: writeback: add bg_threshold parameter to __bdi_update_bandwidth() No behavior change. Signed-off-by: Wu Fengguang --- include/linux/writeback.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux/writeback.h') diff --git a/include/linux/writeback.h b/include/linux/writeback.h index 2b8963ff0f35..ddb4652cb337 100644 --- a/include/linux/writeback.h +++ b/include/linux/writeback.h @@ -143,6 +143,7 @@ unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, void __bdi_update_bandwidth(struct backing_dev_info *bdi, unsigned long thresh, + unsigned long bg_thresh, unsigned long dirty, unsigned long bdi_thresh, unsigned long bdi_dirty, -- cgit v1.2.3 From 0e175a1835ffc979e55787774e58ec79e41957d7 Mon Sep 17 00:00:00 2001 From: Curt Wohlgemuth Date: Fri, 7 Oct 2011 21:54:10 -0600 Subject: writeback: Add a 'reason' to wb_writeback_work This creates a new 'reason' field in a wb_writeback_work structure, which unambiguously identifies who initiates writeback activity. A 'wb_reason' enumeration has been added to writeback.h, to enumerate the possible reasons. The 'writeback_work_class' and tracepoint event class and 'writeback_queue_io' tracepoints are updated to include the symbolic 'reason' in all trace events. And the 'writeback_inodes_sbXXX' family of routines has had a wb_stats parameter added to them, so callers can specify why writeback is being started. Acked-by: Jan Kara Signed-off-by: Curt Wohlgemuth Signed-off-by: Wu Fengguang --- include/linux/writeback.h | 32 ++++++++++++++++++++++++++------ 1 file changed, 26 insertions(+), 6 deletions(-) (limited to 'include/linux/writeback.h') diff --git a/include/linux/writeback.h b/include/linux/writeback.h index ddb4652cb337..a378c295851f 100644 --- a/include/linux/writeback.h +++ b/include/linux/writeback.h @@ -38,6 +38,23 @@ enum writeback_sync_modes { WB_SYNC_ALL, /* Wait on every mapping */ }; +/* + * why some writeback work was initiated + */ +enum wb_reason { + WB_REASON_BACKGROUND, + WB_REASON_TRY_TO_FREE_PAGES, + WB_REASON_SYNC, + WB_REASON_PERIODIC, + WB_REASON_LAPTOP_TIMER, + WB_REASON_FREE_MORE_MEM, + WB_REASON_FS_FREE_SPACE, + WB_REASON_FORKER_THREAD, + + WB_REASON_MAX, +}; +extern const char *wb_reason_name[]; + /* * A control structure which tells the writeback code what to do. These are * always on the stack, and hence need no locking. They are always initialised @@ -69,14 +86,17 @@ struct writeback_control { */ struct bdi_writeback; int inode_wait(void *); -void writeback_inodes_sb(struct super_block *); -void writeback_inodes_sb_nr(struct super_block *, unsigned long nr); -int writeback_inodes_sb_if_idle(struct super_block *); -int writeback_inodes_sb_nr_if_idle(struct super_block *, unsigned long nr); +void writeback_inodes_sb(struct super_block *, enum wb_reason reason); +void writeback_inodes_sb_nr(struct super_block *, unsigned long nr, + enum wb_reason reason); +int writeback_inodes_sb_if_idle(struct super_block *, enum wb_reason reason); +int writeback_inodes_sb_nr_if_idle(struct super_block *, unsigned long nr, + enum wb_reason reason); void sync_inodes_sb(struct super_block *); -long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages); +long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages, + enum wb_reason reason); long wb_do_writeback(struct bdi_writeback *wb, int force_wait); -void wakeup_flusher_threads(long nr_pages); +void wakeup_flusher_threads(long nr_pages, enum wb_reason reason); /* writeback.h requires fs.h; it, too, is not included from here. */ static inline void wait_on_inode(struct inode *inode) -- cgit v1.2.3