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Merge branch 'writeback-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg/linux

Browse source 
* 'writeback-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg/linux:
  writeback: move MIN_WRITEBACK_PAGES to fs-writeback.c
  writeback: balanced_rate cannot exceed write bandwidth
  writeback: do strict bdi dirty_exceeded
  writeback: avoid tiny dirty poll intervals
  writeback: max, min and target dirty pause time
  writeback: dirty ratelimit - think time compensation
  btrfs: fix dirtied pages accounting on sub-page writes
  writeback: fix dirtied pages accounting on redirty
  writeback: fix dirtied pages accounting on sub-page writes
  writeback: charge leaked page dirties to active tasks
  writeback: Include all dirty inodes in background writeback
This commit is contained in:
Linus Torvalds 2012-01-10 16:59:59 -08:00
commit 001a541ea9
8 changed files with 231 additions and 70 deletions
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3
fs/btrfs/file.c
View file

@ -1136,7 +1136,8 @@ static noinline int prepare_pages(struct btrfs_root *root, struct file *file,
GFP_NOFS);
}
for (i = 0; i < num_pages; i++) {
clear_page_dirty_for_io(pages[i]);
if (clear_page_dirty_for_io(pages[i]))
account_page_redirty(pages[i]);
set_page_extent_mapped(pages[i]);
WARN_ON(!PageLocked(pages[i]));
}

16
fs/fs-writeback.c
View file

@ -20,6 +20,7 @@
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
#include <linux/writeback.h>
@ -28,6 +29,11 @@
#include <linux/tracepoint.h>
#include "internal.h"
/*
* 4MB minimal write chunk size
*/
#define MIN_WRITEBACK_PAGES (4096UL >> (PAGE_CACHE_SHIFT - 10))
/*
* Passed into wb_writeback(), essentially a subset of writeback_control
*/
@ -742,11 +748,17 @@ static long wb_writeback(struct bdi_writeback *wb,
if (work->for_background && !over_bground_thresh(wb->bdi))
break;
/*
* Kupdate and background works are special and we want to
* include all inodes that need writing. Livelock avoidance is
* handled by these works yielding to any other work so we are
* safe.
*/
if (work->for_kupdate) {
oldest_jif = jiffies -
msecs_to_jiffies(dirty_expire_interval * 10);
work->older_than_this = &oldest_jif;
}
} else if (work->for_background)
oldest_jif = jiffies;
trace_writeback_start(wb->bdi, work);
if (list_empty(&wb->b_io))

1
include/linux/sched.h
View file

@ -1544,6 +1544,7 @@ 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;

9
include/linux/writeback.h
View file

@ -7,6 +7,8 @@
#include <linux/sched.h>
#include <linux/fs.h>
DECLARE_PER_CPU(int, dirty_throttle_leaks);
/*
* The 1/4 region under the global dirty thresh is for smooth dirty throttling:
*
@ -23,11 +25,6 @@
#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;
/*
@ -194,6 +191,8 @@ 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. */

14
include/trace/events/writeback.h
View file

@ -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 */
)
);

3
kernel/exit.c
View file

@ -51,6 +51,7 @@
#include <trace/events/sched.h>
#include <linux/hw_breakpoint.h>
#include <linux/oom.h>
#include <linux/writeback.h>
#include <asm/uaccess.h>
#include <asm/unistd.h>
@ -1035,6 +1036,8 @@ NORET_TYPE void do_exit(long code)
validate_creds_for_do_exit(tsk);
preempt_disable();
if (tsk->nr_dirtied)
__this_cpu_add(dirty_throttle_leaks, tsk->nr_dirtied);
exit_rcu();
/* causes final put_task_struct in finish_task_switch(). */
tsk->state = TASK_DEAD;

1
kernel/fork.c
View file

@ -1294,6 +1294,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
p->nr_dirtied = 0;
p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);
p->dirty_paused_when = 0;
/*
* Ok, make it visible to the rest of the system.

254
mm/page-writeback.c
View file

@ -41,6 +41,12 @@
*/
#define MAX_PAUSE max(HZ/5, 1)
/*
* Try to keep balance_dirty_pages() call intervals higher than this many pages
* by raising pause time to max_pause when falls below it.
*/
#define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
/*
* Estimate write bandwidth at 200ms intervals.
*/
@ -898,6 +904,11 @@ static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
*/
balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
dirty_rate | 1);
/*
* balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
*/
if (unlikely(balanced_dirty_ratelimit > write_bw))
balanced_dirty_ratelimit = write_bw;
/*
* We could safely do this and return immediately:
@ -1044,25 +1055,11 @@ static unsigned long dirty_poll_interval(unsigned long dirty,
return 1;
}
static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
unsigned long bdi_dirty)
static long bdi_max_pause(struct backing_dev_info *bdi,
unsigned long bdi_dirty)
{
unsigned long bw = bdi->avg_write_bandwidth;
unsigned long hi = ilog2(bw);
unsigned long lo = ilog2(bdi->dirty_ratelimit);
unsigned long t;
/* target for 20ms max pause on 1-dd case */
t = HZ / 50;
/*
* Scale up pause time for concurrent dirtiers in order to reduce CPU
* overheads.
*
* (N * 20ms) on 2^N concurrent tasks.
*/
if (hi > lo)
t += (hi - lo) * (20 * HZ) / 1024;
long bw = bdi->avg_write_bandwidth;
long t;
/*
* Limit pause time for small memory systems. If sleeping for too long
@ -1071,13 +1068,85 @@ static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
*
* 8 serves as the safety ratio.
*/
t = min(t, bdi_dirty * HZ / (8 * bw + 1));
t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
t++;
return min_t(long, t, MAX_PAUSE);
}
static long bdi_min_pause(struct backing_dev_info *bdi,
long max_pause,
unsigned long task_ratelimit,
unsigned long dirty_ratelimit,
int *nr_dirtied_pause)
{
long hi = ilog2(bdi->avg_write_bandwidth);
long lo = ilog2(bdi->dirty_ratelimit);
long t; /* target pause */
long pause; /* estimated next pause */
int pages; /* target nr_dirtied_pause */
/* target for 10ms pause on 1-dd case */
t = max(1, HZ / 100);
/*
* The pause time will be settled within range (max_pause/4, max_pause).
* Apply a minimal value of 4 to get a non-zero max_pause/4.
* Scale up pause time for concurrent dirtiers in order to reduce CPU
* overheads.
*
* (N * 10ms) on 2^N concurrent tasks.
*/
return clamp_val(t, 4, MAX_PAUSE);
if (hi > lo)
t += (hi - lo) * (10 * HZ) / 1024;
/*
* This is a bit convoluted. We try to base the next nr_dirtied_pause
* on the much more stable dirty_ratelimit. However the next pause time
* will be computed based on task_ratelimit and the two rate limits may
* depart considerably at some time. Especially if task_ratelimit goes
* below dirty_ratelimit/2 and the target pause is max_pause, the next
* pause time will be max_pause*2 _trimmed down_ to max_pause. As a
* result task_ratelimit won't be executed faithfully, which could
* eventually bring down dirty_ratelimit.
*
* We apply two rules to fix it up:
* 1) try to estimate the next pause time and if necessary, use a lower
* nr_dirtied_pause so as not to exceed max_pause. When this happens,
* nr_dirtied_pause will be "dancing" with task_ratelimit.
* 2) limit the target pause time to max_pause/2, so that the normal
* small fluctuations of task_ratelimit won't trigger rule (1) and
* nr_dirtied_pause will remain as stable as dirty_ratelimit.
*/
t = min(t, 1 + max_pause / 2);
pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
/*
* Tiny nr_dirtied_pause is found to hurt I/O performance in the test
* case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
* When the 16 consecutive reads are often interrupted by some dirty
* throttling pause during the async writes, cfq will go into idles
* (deadline is fine). So push nr_dirtied_pause as high as possible
* until reaches DIRTY_POLL_THRESH=32 pages.
*/
if (pages < DIRTY_POLL_THRESH) {
t = max_pause;
pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
if (pages > DIRTY_POLL_THRESH) {
pages = DIRTY_POLL_THRESH;
t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
}
}
pause = HZ * pages / (task_ratelimit + 1);
if (pause > max_pause) {
t = max_pause;
pages = task_ratelimit * t / roundup_pow_of_two(HZ);
}
*nr_dirtied_pause = pages;
/*
* The minimal pause time will normally be half the target pause time.
*/
return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
}
/*
@ -1098,16 +1167,21 @@ static void balance_dirty_pages(struct address_space *mapping,
unsigned long background_thresh;
unsigned long dirty_thresh;
unsigned long bdi_thresh;
long pause = 0;
long uninitialized_var(max_pause);
long period;
long pause;
long max_pause;
long min_pause;
int nr_dirtied_pause;
bool dirty_exceeded = false;
unsigned long task_ratelimit;
unsigned long uninitialized_var(dirty_ratelimit);
unsigned long dirty_ratelimit;
unsigned long pos_ratio;
struct backing_dev_info *bdi = mapping->backing_dev_info;
unsigned long start_time = jiffies;
for (;;) {
unsigned long now = jiffies;
/*
* Unstable writes are a feature of certain networked
* filesystems (i.e. NFS) in which data may have been
@ -1127,8 +1201,13 @@ static void balance_dirty_pages(struct address_space *mapping,
*/
freerun = dirty_freerun_ceiling(dirty_thresh,
background_thresh);
if (nr_dirty <= freerun)
if (nr_dirty <= freerun) {
current->dirty_paused_when = now;
current->nr_dirtied = 0;
current->nr_dirtied_pause =
dirty_poll_interval(nr_dirty, dirty_thresh);
break;
}
if (unlikely(!writeback_in_progress(bdi)))
bdi_start_background_writeback(bdi);
@ -1168,7 +1247,7 @@ static void balance_dirty_pages(struct address_space *mapping,
bdi_stat(bdi, BDI_WRITEBACK);
}
dirty_exceeded = (bdi_dirty > bdi_thresh) ||
dirty_exceeded = (bdi_dirty > bdi_thresh) &&
(nr_dirty > dirty_thresh);
if (dirty_exceeded && !bdi->dirty_exceeded)
bdi->dirty_exceeded = 1;
@ -1177,20 +1256,34 @@ static void balance_dirty_pages(struct address_space *mapping,
nr_dirty, bdi_thresh, bdi_dirty,
start_time);
max_pause = bdi_max_pause(bdi, bdi_dirty);
dirty_ratelimit = bdi->dirty_ratelimit;
pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
background_thresh, nr_dirty,
bdi_thresh, bdi_dirty);
task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
RATELIMIT_CALC_SHIFT;
max_pause = bdi_max_pause(bdi, bdi_dirty);
min_pause = bdi_min_pause(bdi, max_pause,
task_ratelimit, dirty_ratelimit,
&nr_dirtied_pause);
if (unlikely(task_ratelimit == 0)) {
period = max_pause;
pause = max_pause;
goto pause;
}
pause = HZ * pages_dirtied / task_ratelimit;
if (unlikely(pause <= 0)) {
period = HZ * pages_dirtied / task_ratelimit;
pause = period;
if (current->dirty_paused_when)
pause -= now - current->dirty_paused_when;
/*
* For less than 1s think time (ext3/4 may block the dirtier
* for up to 800ms from time to time on 1-HDD; so does xfs,
* however at much less frequency), try to compensate it in
* future periods by updating the virtual time; otherwise just
* do a reset, as it may be a light dirtier.
*/
if (pause < min_pause) {
trace_balance_dirty_pages(bdi,
dirty_thresh,
background_thresh,
@ -1200,12 +1293,24 @@ static void balance_dirty_pages(struct address_space *mapping,
dirty_ratelimit,
task_ratelimit,
pages_dirtied,
pause,
period,
min(pause, 0L),
start_time);
pause = 1; /* avoid resetting nr_dirtied_pause below */
if (pause < -HZ) {
current->dirty_paused_when = now;
current->nr_dirtied = 0;
} else if (period) {
current->dirty_paused_when += period;
current->nr_dirtied = 0;
} else if (current->nr_dirtied_pause <= pages_dirtied)
current->nr_dirtied_pause += pages_dirtied;
break;
}
pause = min(pause, max_pause);
if (unlikely(pause > max_pause)) {
/* for occasional dropped task_ratelimit */
now += min(pause - max_pause, max_pause);
pause = max_pause;
}
pause:
trace_balance_dirty_pages(bdi,
@ -1217,11 +1322,16 @@ static void balance_dirty_pages(struct address_space *mapping,
dirty_ratelimit,
task_ratelimit,
pages_dirtied,
period,
pause,
start_time);
__set_current_state(TASK_KILLABLE);
io_schedule_timeout(pause);
current->dirty_paused_when = now + pause;
current->nr_dirtied = 0;
current->nr_dirtied_pause = nr_dirtied_pause;
/*
* This is typically equal to (nr_dirty < dirty_thresh) and can
* also keep "1000+ dd on a slow USB stick" under control.
@ -1249,23 +1359,6 @@ static void balance_dirty_pages(struct address_space *mapping,
if (!dirty_exceeded && bdi->dirty_exceeded)
bdi->dirty_exceeded = 0;
current->nr_dirtied = 0;
if (pause == 0) { /* in freerun area */
current->nr_dirtied_pause =
dirty_poll_interval(nr_dirty, dirty_thresh);
} else if (pause <= max_pause / 4 &&
pages_dirtied >= current->nr_dirtied_pause) {
current->nr_dirtied_pause = clamp_val(
dirty_ratelimit * (max_pause / 2) / HZ,
pages_dirtied + pages_dirtied / 8,
pages_dirtied * 4);
} else if (pause >= max_pause) {
current->nr_dirtied_pause = 1 | clamp_val(
dirty_ratelimit * (max_pause / 2) / HZ,
pages_dirtied / 4,
pages_dirtied - pages_dirtied / 8);
}
if (writeback_in_progress(bdi))
return;
@ -1296,6 +1389,22 @@ void set_page_dirty_balance(struct page *page, int page_mkwrite)
static DEFINE_PER_CPU(int, bdp_ratelimits);
/*
* Normal tasks are throttled by
* loop {
* dirty tsk->nr_dirtied_pause pages;
* take a snap in balance_dirty_pages();
* }
* However there is a worst case. If every task exit immediately when dirtied
* (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
* called to throttle the page dirties. The solution is to save the not yet
* throttled page dirties in dirty_throttle_leaks on task exit and charge them
* randomly into the running tasks. This works well for the above worst case,
* as the new task will pick up and accumulate the old task's leaked dirty
* count and eventually get throttled.
*/
DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
/**
* balance_dirty_pages_ratelimited_nr - balance dirty memory state
* @mapping: address_space which was dirtied
@ -1324,8 +1433,6 @@ void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
if (bdi->dirty_exceeded)
ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
current->nr_dirtied += nr_pages_dirtied;
preempt_disable();
/*
* This prevents one CPU to accumulate too many dirtied pages without
@ -1336,12 +1443,20 @@ void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
p = &__get_cpu_var(bdp_ratelimits);
if (unlikely(current->nr_dirtied >= ratelimit))
*p = 0;
else {
*p += nr_pages_dirtied;
if (unlikely(*p >= ratelimit_pages)) {
*p = 0;
ratelimit = 0;
}
else if (unlikely(*p >= ratelimit_pages)) {
*p = 0;
ratelimit = 0;
}
/*
* Pick up the dirtied pages by the exited tasks. This avoids lots of
* short-lived tasks (eg. gcc invocations in a kernel build) escaping
* the dirty throttling and livelock other long-run dirtiers.
*/
p = &__get_cpu_var(dirty_throttle_leaks);
if (*p > 0 && current->nr_dirtied < ratelimit) {
nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
*p -= nr_pages_dirtied;
current->nr_dirtied += nr_pages_dirtied;
}
preempt_enable();
@ -1823,6 +1938,8 @@ void account_page_dirtied(struct page *page, struct address_space *mapping)
__inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
__inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
task_io_account_write(PAGE_CACHE_SIZE);
current->nr_dirtied++;
this_cpu_inc(bdp_ratelimits);
}
}
EXPORT_SYMBOL(account_page_dirtied);
@ -1882,6 +1999,24 @@ int __set_page_dirty_nobuffers(struct page *page)
}
EXPORT_SYMBOL(__set_page_dirty_nobuffers);
/*
* Call this whenever redirtying a page, to de-account the dirty counters
* (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
* counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
* systematic errors in balanced_dirty_ratelimit and the dirty pages position
* control.
*/
void account_page_redirty(struct page *page)
{
struct address_space *mapping = page->mapping;
if (mapping && mapping_cap_account_dirty(mapping)) {
current->nr_dirtied--;
dec_zone_page_state(page, NR_DIRTIED);
dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
}
}
EXPORT_SYMBOL(account_page_redirty);
/*
* When a writepage implementation decides that it doesn't want to write this
* page for some reason, it should redirty the locked page via
@ -1890,6 +2025,7 @@ EXPORT_SYMBOL(__set_page_dirty_nobuffers);
int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
{
wbc->pages_skipped++;
account_page_redirty(page);
return __set_page_dirty_nobuffers(page);
}
EXPORT_SYMBOL(redirty_page_for_writepage);