From 54848d73f9f254631303d6eab9b976855988b266 Mon Sep 17 00:00:00 2001 From: Wu Fengguang Date: Tue, 5 Apr 2011 13:21:19 -0600 Subject: writeback: charge leaked page dirties to active tasks It's a years long problem that a large number of short-lived dirtiers (eg. gcc instances in a fast kernel build) may starve long-run dirtiers (eg. dd) as well as pushing the dirty pages to the global hard limit. The solution is to charge the pages dirtied by the exited gcc to the other random dirtying tasks. It sounds not perfect, however should behave good enough in practice, seeing as that throttled tasks aren't actually running so those that are running are more likely to pick it up and get throttled, therefore promoting an equal spread. Randy: fix compile error: 'dirty_throttle_leaks' undeclared in exit.c Acked-by: Jan Kara Acked-by: Peter Zijlstra Signed-off-by: Randy Dunlap Signed-off-by: Wu Fengguang --- include/linux/writeback.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include') diff --git a/include/linux/writeback.h b/include/linux/writeback.h index a378c295851f..05eaf5e3aad7 100644 --- a/include/linux/writeback.h +++ b/include/linux/writeback.h @@ -7,6 +7,8 @@ #include #include +DECLARE_PER_CPU(int, dirty_throttle_leaks); + /* * The 1/4 region under the global dirty thresh is for smooth dirty throttling: * -- cgit v1.2.2 From 2f800fbd777b792de54187088df19a7df0251254 Mon Sep 17 00:00:00 2001 From: Wu Fengguang Date: Mon, 8 Aug 2011 15:22:00 -0600 Subject: writeback: fix dirtied pages accounting on redirty De-account the accumulative dirty counters on page redirty. Page redirties (very common in ext4) will introduce mismatch between counters (a) and (b) a) NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied b) NR_WRITTEN, BDI_WRITTEN This will introduce systematic errors in balanced_rate and result in dirty page position errors (ie. the dirty pages are no longer balanced around the global/bdi setpoints). Acked-by: Jan Kara Acked-by: Peter Zijlstra Signed-off-by: Wu Fengguang --- include/linux/writeback.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include') diff --git a/include/linux/writeback.h b/include/linux/writeback.h index 05eaf5e3aad7..b30419cd425e 100644 --- a/include/linux/writeback.h +++ b/include/linux/writeback.h @@ -197,6 +197,8 @@ void writeback_set_ratelimit(void); void tag_pages_for_writeback(struct address_space *mapping, pgoff_t start, pgoff_t end); +void account_page_redirty(struct page *page); + /* pdflush.c */ extern int nr_pdflush_threads; /* Global so it can be exported to sysctl read-only. */ -- cgit v1.2.2 From 83712358ba0a1497ce59a4f84ce4dd0f803fe6fc Mon Sep 17 00:00:00 2001 From: Wu Fengguang Date: Sat, 11 Jun 2011 19:25:42 -0600 Subject: writeback: dirty ratelimit - think time compensation Compensate the task's think time when computing the final pause time, so that ->dirty_ratelimit can be executed accurately. think time := time spend outside of balance_dirty_pages() In the rare case that the task slept longer than the 200ms period time (result in negative pause time), the sleep time will be compensated in the following periods, too, if it's less than 1 second. Accumulated errors are carefully avoided as long as the max pause area is not hitted. Pseudo code: period = pages_dirtied / task_ratelimit; think = jiffies - dirty_paused_when; pause = period - think; 1) normal case: period > think pause = period - think dirty_paused_when = jiffies + pause nr_dirtied = 0 period time |===============================>| think time pause time |===============>|==============>| ------|----------------|---------------|------------------------ dirty_paused_when jiffies 2) no pause case: period <= think don't pause; reduce future pause time by: dirty_paused_when += period nr_dirtied = 0 period time |===============================>| think time |===================================================>| ------|--------------------------------+-------------------|---- dirty_paused_when jiffies Acked-by: Jan Kara Acked-by: Peter Zijlstra Signed-off-by: Wu Fengguang --- include/linux/sched.h | 1 + include/trace/events/writeback.h | 14 +++++++++++--- 2 files changed, 12 insertions(+), 3 deletions(-) (limited to 'include') diff --git a/include/linux/sched.h b/include/linux/sched.h index 1c4f3e9b9bc5..984c3b295978 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1527,6 +1527,7 @@ struct task_struct { */ int nr_dirtied; int nr_dirtied_pause; + unsigned long dirty_paused_when; /* start of a write-and-pause period */ #ifdef CONFIG_LATENCYTOP int latency_record_count; diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h index 99d1d0decf88..8588a8918023 100644 --- a/include/trace/events/writeback.h +++ b/include/trace/events/writeback.h @@ -300,12 +300,13 @@ TRACE_EVENT(balance_dirty_pages, unsigned long dirty_ratelimit, unsigned long task_ratelimit, unsigned long dirtied, + unsigned long period, long pause, unsigned long start_time), TP_ARGS(bdi, thresh, bg_thresh, dirty, bdi_thresh, bdi_dirty, dirty_ratelimit, task_ratelimit, - dirtied, pause, start_time), + dirtied, period, pause, start_time), TP_STRUCT__entry( __array( char, bdi, 32) @@ -320,6 +321,8 @@ TRACE_EVENT(balance_dirty_pages, __field(unsigned int, dirtied_pause) __field(unsigned long, paused) __field( long, pause) + __field(unsigned long, period) + __field( long, think) ), TP_fast_assign( @@ -336,6 +339,9 @@ TRACE_EVENT(balance_dirty_pages, __entry->task_ratelimit = KBps(task_ratelimit); __entry->dirtied = dirtied; __entry->dirtied_pause = current->nr_dirtied_pause; + __entry->think = current->dirty_paused_when == 0 ? 0 : + (long)(jiffies - current->dirty_paused_when) * 1000/HZ; + __entry->period = period * 1000 / HZ; __entry->pause = pause * 1000 / HZ; __entry->paused = (jiffies - start_time) * 1000 / HZ; ), @@ -346,7 +352,7 @@ TRACE_EVENT(balance_dirty_pages, "bdi_setpoint=%lu bdi_dirty=%lu " "dirty_ratelimit=%lu task_ratelimit=%lu " "dirtied=%u dirtied_pause=%u " - "paused=%lu pause=%ld", + "paused=%lu pause=%ld period=%lu think=%ld", __entry->bdi, __entry->limit, __entry->setpoint, @@ -358,7 +364,9 @@ TRACE_EVENT(balance_dirty_pages, __entry->dirtied, __entry->dirtied_pause, __entry->paused, /* ms */ - __entry->pause /* ms */ + __entry->pause, /* ms */ + __entry->period, /* ms */ + __entry->think /* ms */ ) ); -- cgit v1.2.2 From bc31b86a5923fad5f3fbb6192f767f410241ba27 Mon Sep 17 00:00:00 2001 From: Wu Fengguang Date: Sat, 7 Jan 2012 20:41:55 -0600 Subject: writeback: move MIN_WRITEBACK_PAGES to fs-writeback.c MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Fix compile error fs/fs-writeback.c:515:33: error: ‘PAGE_CACHE_SHIFT’ undeclared (first use in this function) Reported-by: Randy Dunlap Acked-by: Randy Dunlap Signed-off-by: Wu Fengguang --- include/linux/writeback.h | 5 ----- 1 file changed, 5 deletions(-) (limited to 'include') diff --git a/include/linux/writeback.h b/include/linux/writeback.h index b30419cd425e..4e0a55493023 100644 --- a/include/linux/writeback.h +++ b/include/linux/writeback.h @@ -25,11 +25,6 @@ DECLARE_PER_CPU(int, dirty_throttle_leaks); #define DIRTY_SCOPE 8 #define DIRTY_FULL_SCOPE (DIRTY_SCOPE / 2) -/* - * 4MB minimal write chunk size - */ -#define MIN_WRITEBACK_PAGES (4096UL >> (PAGE_CACHE_SHIFT - 10)) - struct backing_dev_info; /* -- cgit v1.2.2