linux/mm/page-writeback.c
David Rientjes 2da02997e0 mm: add dirty_background_bytes and dirty_bytes sysctls
This change introduces two new sysctls to /proc/sys/vm:
dirty_background_bytes and dirty_bytes.

dirty_background_bytes is the counterpart to dirty_background_ratio and
dirty_bytes is the counterpart to dirty_ratio.

With growing memory capacities of individual machines, it's no longer
sufficient to specify dirty thresholds as a percentage of the amount of
dirtyable memory over the entire system.

dirty_background_bytes and dirty_bytes specify quantities of memory, in
bytes, that represent the dirty limits for the entire system.  If either
of these values is set, its value represents the amount of dirty memory
that is needed to commence either background or direct writeback.

When a `bytes' or `ratio' file is written, its counterpart becomes a
function of the written value.  For example, if dirty_bytes is written to
be 8096, 8K of memory is required to commence direct writeback.
dirty_ratio is then functionally equivalent to 8K / the amount of
dirtyable memory:

	dirtyable_memory = free pages + mapped pages + file cache

	dirty_background_bytes = dirty_background_ratio * dirtyable_memory
		-or-
	dirty_background_ratio = dirty_background_bytes / dirtyable_memory

		AND

	dirty_bytes = dirty_ratio * dirtyable_memory
		-or-
	dirty_ratio = dirty_bytes / dirtyable_memory

Only one of dirty_background_bytes and dirty_background_ratio may be
specified at a time, and only one of dirty_bytes and dirty_ratio may be
specified.  When one sysctl is written, the other appears as 0 when read.

The `bytes' files operate on a page size granularity since dirty limits
are compared with ZVC values, which are in page units.

Prior to this change, the minimum dirty_ratio was 5 as implemented by
get_dirty_limits() although /proc/sys/vm/dirty_ratio would show any user
written value between 0 and 100.  This restriction is maintained, but
dirty_bytes has a lower limit of only one page.

Also prior to this change, the dirty_background_ratio could not equal or
exceed dirty_ratio.  This restriction is maintained in addition to
restricting dirty_background_bytes.  If either background threshold equals
or exceeds that of the dirty threshold, it is implicitly set to half the
dirty threshold.

Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: David Rientjes <rientjes@google.com>
Cc: Andrea Righi <righi.andrea@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-01-06 15:59:03 -08:00

1448 lines
39 KiB
C

/*
* mm/page-writeback.c
*
* Copyright (C) 2002, Linus Torvalds.
* Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
*
* Contains functions related to writing back dirty pages at the
* address_space level.
*
* 10Apr2002 Andrew Morton
* Initial version
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/slab.h>
#include <linux/pagemap.h>
#include <linux/writeback.h>
#include <linux/init.h>
#include <linux/backing-dev.h>
#include <linux/task_io_accounting_ops.h>
#include <linux/blkdev.h>
#include <linux/mpage.h>
#include <linux/rmap.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/smp.h>
#include <linux/sysctl.h>
#include <linux/cpu.h>
#include <linux/syscalls.h>
#include <linux/buffer_head.h>
#include <linux/pagevec.h>
/*
* The maximum number of pages to writeout in a single bdflush/kupdate
* operation. We do this so we don't hold I_SYNC against an inode for
* enormous amounts of time, which would block a userspace task which has
* been forced to throttle against that inode. Also, the code reevaluates
* the dirty each time it has written this many pages.
*/
#define MAX_WRITEBACK_PAGES 1024
/*
* After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
* will look to see if it needs to force writeback or throttling.
*/
static long ratelimit_pages = 32;
/*
* When balance_dirty_pages decides that the caller needs to perform some
* non-background writeback, this is how many pages it will attempt to write.
* It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably
* large amounts of I/O are submitted.
*/
static inline long sync_writeback_pages(void)
{
return ratelimit_pages + ratelimit_pages / 2;
}
/* The following parameters are exported via /proc/sys/vm */
/*
* Start background writeback (via pdflush) at this percentage
*/
int dirty_background_ratio = 5;
/*
* dirty_background_bytes starts at 0 (disabled) so that it is a function of
* dirty_background_ratio * the amount of dirtyable memory
*/
unsigned long dirty_background_bytes;
/*
* free highmem will not be subtracted from the total free memory
* for calculating free ratios if vm_highmem_is_dirtyable is true
*/
int vm_highmem_is_dirtyable;
/*
* The generator of dirty data starts writeback at this percentage
*/
int vm_dirty_ratio = 10;
/*
* vm_dirty_bytes starts at 0 (disabled) so that it is a function of
* vm_dirty_ratio * the amount of dirtyable memory
*/
unsigned long vm_dirty_bytes;
/*
* The interval between `kupdate'-style writebacks, in jiffies
*/
int dirty_writeback_interval = 5 * HZ;
/*
* The longest number of jiffies for which data is allowed to remain dirty
*/
int dirty_expire_interval = 30 * HZ;
/*
* Flag that makes the machine dump writes/reads and block dirtyings.
*/
int block_dump;
/*
* Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
* a full sync is triggered after this time elapses without any disk activity.
*/
int laptop_mode;
EXPORT_SYMBOL(laptop_mode);
/* End of sysctl-exported parameters */
static void background_writeout(unsigned long _min_pages);
/*
* Scale the writeback cache size proportional to the relative writeout speeds.
*
* We do this by keeping a floating proportion between BDIs, based on page
* writeback completions [end_page_writeback()]. Those devices that write out
* pages fastest will get the larger share, while the slower will get a smaller
* share.
*
* We use page writeout completions because we are interested in getting rid of
* dirty pages. Having them written out is the primary goal.
*
* We introduce a concept of time, a period over which we measure these events,
* because demand can/will vary over time. The length of this period itself is
* measured in page writeback completions.
*
*/
static struct prop_descriptor vm_completions;
static struct prop_descriptor vm_dirties;
/*
* couple the period to the dirty_ratio:
*
* period/2 ~ roundup_pow_of_two(dirty limit)
*/
static int calc_period_shift(void)
{
unsigned long dirty_total;
if (vm_dirty_bytes)
dirty_total = vm_dirty_bytes / PAGE_SIZE;
else
dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) /
100;
return 2 + ilog2(dirty_total - 1);
}
/*
* update the period when the dirty threshold changes.
*/
static void update_completion_period(void)
{
int shift = calc_period_shift();
prop_change_shift(&vm_completions, shift);
prop_change_shift(&vm_dirties, shift);
}
int dirty_background_ratio_handler(struct ctl_table *table, int write,
struct file *filp, void __user *buffer, size_t *lenp,
loff_t *ppos)
{
int ret;
ret = proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos);
if (ret == 0 && write)
dirty_background_bytes = 0;
return ret;
}
int dirty_background_bytes_handler(struct ctl_table *table, int write,
struct file *filp, void __user *buffer, size_t *lenp,
loff_t *ppos)
{
int ret;
ret = proc_doulongvec_minmax(table, write, filp, buffer, lenp, ppos);
if (ret == 0 && write)
dirty_background_ratio = 0;
return ret;
}
int dirty_ratio_handler(struct ctl_table *table, int write,
struct file *filp, void __user *buffer, size_t *lenp,
loff_t *ppos)
{
int old_ratio = vm_dirty_ratio;
int ret;
ret = proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos);
if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
update_completion_period();
vm_dirty_bytes = 0;
}
return ret;
}
int dirty_bytes_handler(struct ctl_table *table, int write,
struct file *filp, void __user *buffer, size_t *lenp,
loff_t *ppos)
{
int old_bytes = vm_dirty_bytes;
int ret;
ret = proc_doulongvec_minmax(table, write, filp, buffer, lenp, ppos);
if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
update_completion_period();
vm_dirty_ratio = 0;
}
return ret;
}
/*
* Increment the BDI's writeout completion count and the global writeout
* completion count. Called from test_clear_page_writeback().
*/
static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
{
__prop_inc_percpu_max(&vm_completions, &bdi->completions,
bdi->max_prop_frac);
}
void bdi_writeout_inc(struct backing_dev_info *bdi)
{
unsigned long flags;
local_irq_save(flags);
__bdi_writeout_inc(bdi);
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(bdi_writeout_inc);
static inline void task_dirty_inc(struct task_struct *tsk)
{
prop_inc_single(&vm_dirties, &tsk->dirties);
}
/*
* Obtain an accurate fraction of the BDI's portion.
*/
static void bdi_writeout_fraction(struct backing_dev_info *bdi,
long *numerator, long *denominator)
{
if (bdi_cap_writeback_dirty(bdi)) {
prop_fraction_percpu(&vm_completions, &bdi->completions,
numerator, denominator);
} else {
*numerator = 0;
*denominator = 1;
}
}
/*
* Clip the earned share of dirty pages to that which is actually available.
* This avoids exceeding the total dirty_limit when the floating averages
* fluctuate too quickly.
*/
static void
clip_bdi_dirty_limit(struct backing_dev_info *bdi, long dirty, long *pbdi_dirty)
{
long avail_dirty;
avail_dirty = dirty -
(global_page_state(NR_FILE_DIRTY) +
global_page_state(NR_WRITEBACK) +
global_page_state(NR_UNSTABLE_NFS) +
global_page_state(NR_WRITEBACK_TEMP));
if (avail_dirty < 0)
avail_dirty = 0;
avail_dirty += bdi_stat(bdi, BDI_RECLAIMABLE) +
bdi_stat(bdi, BDI_WRITEBACK);
*pbdi_dirty = min(*pbdi_dirty, avail_dirty);
}
static inline void task_dirties_fraction(struct task_struct *tsk,
long *numerator, long *denominator)
{
prop_fraction_single(&vm_dirties, &tsk->dirties,
numerator, denominator);
}
/*
* scale the dirty limit
*
* task specific dirty limit:
*
* dirty -= (dirty/8) * p_{t}
*/
static void task_dirty_limit(struct task_struct *tsk, long *pdirty)
{
long numerator, denominator;
long dirty = *pdirty;
u64 inv = dirty >> 3;
task_dirties_fraction(tsk, &numerator, &denominator);
inv *= numerator;
do_div(inv, denominator);
dirty -= inv;
if (dirty < *pdirty/2)
dirty = *pdirty/2;
*pdirty = dirty;
}
/*
*
*/
static DEFINE_SPINLOCK(bdi_lock);
static unsigned int bdi_min_ratio;
int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
{
int ret = 0;
unsigned long flags;
spin_lock_irqsave(&bdi_lock, flags);
if (min_ratio > bdi->max_ratio) {
ret = -EINVAL;
} else {
min_ratio -= bdi->min_ratio;
if (bdi_min_ratio + min_ratio < 100) {
bdi_min_ratio += min_ratio;
bdi->min_ratio += min_ratio;
} else {
ret = -EINVAL;
}
}
spin_unlock_irqrestore(&bdi_lock, flags);
return ret;
}
int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
{
unsigned long flags;
int ret = 0;
if (max_ratio > 100)
return -EINVAL;
spin_lock_irqsave(&bdi_lock, flags);
if (bdi->min_ratio > max_ratio) {
ret = -EINVAL;
} else {
bdi->max_ratio = max_ratio;
bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
}
spin_unlock_irqrestore(&bdi_lock, flags);
return ret;
}
EXPORT_SYMBOL(bdi_set_max_ratio);
/*
* Work out the current dirty-memory clamping and background writeout
* thresholds.
*
* The main aim here is to lower them aggressively if there is a lot of mapped
* memory around. To avoid stressing page reclaim with lots of unreclaimable
* pages. It is better to clamp down on writers than to start swapping, and
* performing lots of scanning.
*
* We only allow 1/2 of the currently-unmapped memory to be dirtied.
*
* We don't permit the clamping level to fall below 5% - that is getting rather
* excessive.
*
* We make sure that the background writeout level is below the adjusted
* clamping level.
*/
static unsigned long highmem_dirtyable_memory(unsigned long total)
{
#ifdef CONFIG_HIGHMEM
int node;
unsigned long x = 0;
for_each_node_state(node, N_HIGH_MEMORY) {
struct zone *z =
&NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
x += zone_page_state(z, NR_FREE_PAGES) + zone_lru_pages(z);
}
/*
* Make sure that the number of highmem pages is never larger
* than the number of the total dirtyable memory. This can only
* occur in very strange VM situations but we want to make sure
* that this does not occur.
*/
return min(x, total);
#else
return 0;
#endif
}
/**
* determine_dirtyable_memory - amount of memory that may be used
*
* Returns the numebr of pages that can currently be freed and used
* by the kernel for direct mappings.
*/
unsigned long determine_dirtyable_memory(void)
{
unsigned long x;
x = global_page_state(NR_FREE_PAGES) + global_lru_pages();
if (!vm_highmem_is_dirtyable)
x -= highmem_dirtyable_memory(x);
return x + 1; /* Ensure that we never return 0 */
}
void
get_dirty_limits(unsigned long *pbackground, unsigned long *pdirty,
unsigned long *pbdi_dirty, struct backing_dev_info *bdi)
{
unsigned long background;
unsigned long dirty;
unsigned long available_memory = determine_dirtyable_memory();
struct task_struct *tsk;
if (vm_dirty_bytes)
dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
else {
int dirty_ratio;
dirty_ratio = vm_dirty_ratio;
if (dirty_ratio < 5)
dirty_ratio = 5;
dirty = (dirty_ratio * available_memory) / 100;
}
if (dirty_background_bytes)
background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
else
background = (dirty_background_ratio * available_memory) / 100;
if (background >= dirty)
background = dirty / 2;
tsk = current;
if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
background += background / 4;
dirty += dirty / 4;
}
*pbackground = background;
*pdirty = dirty;
if (bdi) {
u64 bdi_dirty;
long numerator, denominator;
/*
* Calculate this BDI's share of the dirty ratio.
*/
bdi_writeout_fraction(bdi, &numerator, &denominator);
bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
bdi_dirty *= numerator;
do_div(bdi_dirty, denominator);
bdi_dirty += (dirty * bdi->min_ratio) / 100;
if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
bdi_dirty = dirty * bdi->max_ratio / 100;
*pbdi_dirty = bdi_dirty;
clip_bdi_dirty_limit(bdi, dirty, pbdi_dirty);
task_dirty_limit(current, pbdi_dirty);
}
}
/*
* balance_dirty_pages() must be called by processes which are generating dirty
* data. It looks at the number of dirty pages in the machine and will force
* the caller to perform writeback if the system is over `vm_dirty_ratio'.
* If we're over `background_thresh' then pdflush is woken to perform some
* writeout.
*/
static void balance_dirty_pages(struct address_space *mapping)
{
long nr_reclaimable, bdi_nr_reclaimable;
long nr_writeback, bdi_nr_writeback;
unsigned long background_thresh;
unsigned long dirty_thresh;
unsigned long bdi_thresh;
unsigned long pages_written = 0;
unsigned long write_chunk = sync_writeback_pages();
struct backing_dev_info *bdi = mapping->backing_dev_info;
for (;;) {
struct writeback_control wbc = {
.bdi = bdi,
.sync_mode = WB_SYNC_NONE,
.older_than_this = NULL,
.nr_to_write = write_chunk,
.range_cyclic = 1,
};
get_dirty_limits(&background_thresh, &dirty_thresh,
&bdi_thresh, bdi);
nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
global_page_state(NR_UNSTABLE_NFS);
nr_writeback = global_page_state(NR_WRITEBACK);
bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
break;
/*
* Throttle it only when the background writeback cannot
* catch-up. This avoids (excessively) small writeouts
* when the bdi limits are ramping up.
*/
if (nr_reclaimable + nr_writeback <
(background_thresh + dirty_thresh) / 2)
break;
if (!bdi->dirty_exceeded)
bdi->dirty_exceeded = 1;
/* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
* Unstable writes are a feature of certain networked
* filesystems (i.e. NFS) in which data may have been
* written to the server's write cache, but has not yet
* been flushed to permanent storage.
*/
if (bdi_nr_reclaimable) {
writeback_inodes(&wbc);
pages_written += write_chunk - wbc.nr_to_write;
get_dirty_limits(&background_thresh, &dirty_thresh,
&bdi_thresh, bdi);
}
/*
* In order to avoid the stacked BDI deadlock we need
* to ensure we accurately count the 'dirty' pages when
* the threshold is low.
*
* Otherwise it would be possible to get thresh+n pages
* reported dirty, even though there are thresh-m pages
* actually dirty; with m+n sitting in the percpu
* deltas.
*/
if (bdi_thresh < 2*bdi_stat_error(bdi)) {
bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK);
} else if (bdi_nr_reclaimable) {
bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
}
if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
break;
if (pages_written >= write_chunk)
break; /* We've done our duty */
congestion_wait(WRITE, HZ/10);
}
if (bdi_nr_reclaimable + bdi_nr_writeback < bdi_thresh &&
bdi->dirty_exceeded)
bdi->dirty_exceeded = 0;
if (writeback_in_progress(bdi))
return; /* pdflush is already working this queue */
/*
* In laptop mode, we wait until hitting the higher threshold before
* starting background writeout, and then write out all the way down
* to the lower threshold. So slow writers cause minimal disk activity.
*
* In normal mode, we start background writeout at the lower
* background_thresh, to keep the amount of dirty memory low.
*/
if ((laptop_mode && pages_written) ||
(!laptop_mode && (global_page_state(NR_FILE_DIRTY)
+ global_page_state(NR_UNSTABLE_NFS)
> background_thresh)))
pdflush_operation(background_writeout, 0);
}
void set_page_dirty_balance(struct page *page, int page_mkwrite)
{
if (set_page_dirty(page) || page_mkwrite) {
struct address_space *mapping = page_mapping(page);
if (mapping)
balance_dirty_pages_ratelimited(mapping);
}
}
/**
* balance_dirty_pages_ratelimited_nr - balance dirty memory state
* @mapping: address_space which was dirtied
* @nr_pages_dirtied: number of pages which the caller has just dirtied
*
* Processes which are dirtying memory should call in here once for each page
* which was newly dirtied. The function will periodically check the system's
* dirty state and will initiate writeback if needed.
*
* On really big machines, get_writeback_state is expensive, so try to avoid
* calling it too often (ratelimiting). But once we're over the dirty memory
* limit we decrease the ratelimiting by a lot, to prevent individual processes
* from overshooting the limit by (ratelimit_pages) each.
*/
void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
unsigned long nr_pages_dirtied)
{
static DEFINE_PER_CPU(unsigned long, ratelimits) = 0;
unsigned long ratelimit;
unsigned long *p;
ratelimit = ratelimit_pages;
if (mapping->backing_dev_info->dirty_exceeded)
ratelimit = 8;
/*
* Check the rate limiting. Also, we do not want to throttle real-time
* tasks in balance_dirty_pages(). Period.
*/
preempt_disable();
p = &__get_cpu_var(ratelimits);
*p += nr_pages_dirtied;
if (unlikely(*p >= ratelimit)) {
*p = 0;
preempt_enable();
balance_dirty_pages(mapping);
return;
}
preempt_enable();
}
EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
void throttle_vm_writeout(gfp_t gfp_mask)
{
unsigned long background_thresh;
unsigned long dirty_thresh;
for ( ; ; ) {
get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
/*
* Boost the allowable dirty threshold a bit for page
* allocators so they don't get DoS'ed by heavy writers
*/
dirty_thresh += dirty_thresh / 10; /* wheeee... */
if (global_page_state(NR_UNSTABLE_NFS) +
global_page_state(NR_WRITEBACK) <= dirty_thresh)
break;
congestion_wait(WRITE, HZ/10);
/*
* The caller might hold locks which can prevent IO completion
* or progress in the filesystem. So we cannot just sit here
* waiting for IO to complete.
*/
if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
break;
}
}
/*
* writeback at least _min_pages, and keep writing until the amount of dirty
* memory is less than the background threshold, or until we're all clean.
*/
static void background_writeout(unsigned long _min_pages)
{
long min_pages = _min_pages;
struct writeback_control wbc = {
.bdi = NULL,
.sync_mode = WB_SYNC_NONE,
.older_than_this = NULL,
.nr_to_write = 0,
.nonblocking = 1,
.range_cyclic = 1,
};
for ( ; ; ) {
unsigned long background_thresh;
unsigned long dirty_thresh;
get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
if (global_page_state(NR_FILE_DIRTY) +
global_page_state(NR_UNSTABLE_NFS) < background_thresh
&& min_pages <= 0)
break;
wbc.more_io = 0;
wbc.encountered_congestion = 0;
wbc.nr_to_write = MAX_WRITEBACK_PAGES;
wbc.pages_skipped = 0;
writeback_inodes(&wbc);
min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
/* Wrote less than expected */
if (wbc.encountered_congestion || wbc.more_io)
congestion_wait(WRITE, HZ/10);
else
break;
}
}
}
/*
* Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back
* the whole world. Returns 0 if a pdflush thread was dispatched. Returns
* -1 if all pdflush threads were busy.
*/
int wakeup_pdflush(long nr_pages)
{
if (nr_pages == 0)
nr_pages = global_page_state(NR_FILE_DIRTY) +
global_page_state(NR_UNSTABLE_NFS);
return pdflush_operation(background_writeout, nr_pages);
}
static void wb_timer_fn(unsigned long unused);
static void laptop_timer_fn(unsigned long unused);
static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0);
static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0);
/*
* Periodic writeback of "old" data.
*
* Define "old": the first time one of an inode's pages is dirtied, we mark the
* dirtying-time in the inode's address_space. So this periodic writeback code
* just walks the superblock inode list, writing back any inodes which are
* older than a specific point in time.
*
* Try to run once per dirty_writeback_interval. But if a writeback event
* takes longer than a dirty_writeback_interval interval, then leave a
* one-second gap.
*
* older_than_this takes precedence over nr_to_write. So we'll only write back
* all dirty pages if they are all attached to "old" mappings.
*/
static void wb_kupdate(unsigned long arg)
{
unsigned long oldest_jif;
unsigned long start_jif;
unsigned long next_jif;
long nr_to_write;
struct writeback_control wbc = {
.bdi = NULL,
.sync_mode = WB_SYNC_NONE,
.older_than_this = &oldest_jif,
.nr_to_write = 0,
.nonblocking = 1,
.for_kupdate = 1,
.range_cyclic = 1,
};
sync_supers();
oldest_jif = jiffies - dirty_expire_interval;
start_jif = jiffies;
next_jif = start_jif + dirty_writeback_interval;
nr_to_write = global_page_state(NR_FILE_DIRTY) +
global_page_state(NR_UNSTABLE_NFS) +
(inodes_stat.nr_inodes - inodes_stat.nr_unused);
while (nr_to_write > 0) {
wbc.more_io = 0;
wbc.encountered_congestion = 0;
wbc.nr_to_write = MAX_WRITEBACK_PAGES;
writeback_inodes(&wbc);
if (wbc.nr_to_write > 0) {
if (wbc.encountered_congestion || wbc.more_io)
congestion_wait(WRITE, HZ/10);
else
break; /* All the old data is written */
}
nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
}
if (time_before(next_jif, jiffies + HZ))
next_jif = jiffies + HZ;
if (dirty_writeback_interval)
mod_timer(&wb_timer, next_jif);
}
/*
* sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
*/
int dirty_writeback_centisecs_handler(ctl_table *table, int write,
struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
{
proc_dointvec_userhz_jiffies(table, write, file, buffer, length, ppos);
if (dirty_writeback_interval)
mod_timer(&wb_timer, jiffies + dirty_writeback_interval);
else
del_timer(&wb_timer);
return 0;
}
static void wb_timer_fn(unsigned long unused)
{
if (pdflush_operation(wb_kupdate, 0) < 0)
mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
}
static void laptop_flush(unsigned long unused)
{
sys_sync();
}
static void laptop_timer_fn(unsigned long unused)
{
pdflush_operation(laptop_flush, 0);
}
/*
* We've spun up the disk and we're in laptop mode: schedule writeback
* of all dirty data a few seconds from now. If the flush is already scheduled
* then push it back - the user is still using the disk.
*/
void laptop_io_completion(void)
{
mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode);
}
/*
* We're in laptop mode and we've just synced. The sync's writes will have
* caused another writeback to be scheduled by laptop_io_completion.
* Nothing needs to be written back anymore, so we unschedule the writeback.
*/
void laptop_sync_completion(void)
{
del_timer(&laptop_mode_wb_timer);
}
/*
* If ratelimit_pages is too high then we can get into dirty-data overload
* if a large number of processes all perform writes at the same time.
* If it is too low then SMP machines will call the (expensive)
* get_writeback_state too often.
*
* Here we set ratelimit_pages to a level which ensures that when all CPUs are
* dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
* thresholds before writeback cuts in.
*
* But the limit should not be set too high. Because it also controls the
* amount of memory which the balance_dirty_pages() caller has to write back.
* If this is too large then the caller will block on the IO queue all the
* time. So limit it to four megabytes - the balance_dirty_pages() caller
* will write six megabyte chunks, max.
*/
void writeback_set_ratelimit(void)
{
ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
if (ratelimit_pages < 16)
ratelimit_pages = 16;
if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
}
static int __cpuinit
ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
{
writeback_set_ratelimit();
return NOTIFY_DONE;
}
static struct notifier_block __cpuinitdata ratelimit_nb = {
.notifier_call = ratelimit_handler,
.next = NULL,
};
/*
* Called early on to tune the page writeback dirty limits.
*
* We used to scale dirty pages according to how total memory
* related to pages that could be allocated for buffers (by
* comparing nr_free_buffer_pages() to vm_total_pages.
*
* However, that was when we used "dirty_ratio" to scale with
* all memory, and we don't do that any more. "dirty_ratio"
* is now applied to total non-HIGHPAGE memory (by subtracting
* totalhigh_pages from vm_total_pages), and as such we can't
* get into the old insane situation any more where we had
* large amounts of dirty pages compared to a small amount of
* non-HIGHMEM memory.
*
* But we might still want to scale the dirty_ratio by how
* much memory the box has..
*/
void __init page_writeback_init(void)
{
int shift;
mod_timer(&wb_timer, jiffies + dirty_writeback_interval);
writeback_set_ratelimit();
register_cpu_notifier(&ratelimit_nb);
shift = calc_period_shift();
prop_descriptor_init(&vm_completions, shift);
prop_descriptor_init(&vm_dirties, shift);
}
/**
* write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
* @mapping: address space structure to write
* @wbc: subtract the number of written pages from *@wbc->nr_to_write
* @writepage: function called for each page
* @data: data passed to writepage function
*
* If a page is already under I/O, write_cache_pages() skips it, even
* if it's dirty. This is desirable behaviour for memory-cleaning writeback,
* but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
* and msync() need to guarantee that all the data which was dirty at the time
* the call was made get new I/O started against them. If wbc->sync_mode is
* WB_SYNC_ALL then we were called for data integrity and we must wait for
* existing IO to complete.
*/
int write_cache_pages(struct address_space *mapping,
struct writeback_control *wbc, writepage_t writepage,
void *data)
{
struct backing_dev_info *bdi = mapping->backing_dev_info;
int ret = 0;
int done = 0;
struct pagevec pvec;
int nr_pages;
pgoff_t uninitialized_var(writeback_index);
pgoff_t index;
pgoff_t end; /* Inclusive */
pgoff_t done_index;
int cycled;
int range_whole = 0;
long nr_to_write = wbc->nr_to_write;
if (wbc->nonblocking && bdi_write_congested(bdi)) {
wbc->encountered_congestion = 1;
return 0;
}
pagevec_init(&pvec, 0);
if (wbc->range_cyclic) {
writeback_index = mapping->writeback_index; /* prev offset */
index = writeback_index;
if (index == 0)
cycled = 1;
else
cycled = 0;
end = -1;
} else {
index = wbc->range_start >> PAGE_CACHE_SHIFT;
end = wbc->range_end >> PAGE_CACHE_SHIFT;
if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
range_whole = 1;
cycled = 1; /* ignore range_cyclic tests */
}
retry:
done_index = index;
while (!done && (index <= end)) {
int i;
nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
PAGECACHE_TAG_DIRTY,
min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
if (nr_pages == 0)
break;
for (i = 0; i < nr_pages; i++) {
struct page *page = pvec.pages[i];
/*
* At this point, the page may be truncated or
* invalidated (changing page->mapping to NULL), or
* even swizzled back from swapper_space to tmpfs file
* mapping. However, page->index will not change
* because we have a reference on the page.
*/
if (page->index > end) {
/*
* can't be range_cyclic (1st pass) because
* end == -1 in that case.
*/
done = 1;
break;
}
done_index = page->index + 1;
lock_page(page);
/*
* Page truncated or invalidated. We can freely skip it
* then, even for data integrity operations: the page
* has disappeared concurrently, so there could be no
* real expectation of this data interity operation
* even if there is now a new, dirty page at the same
* pagecache address.
*/
if (unlikely(page->mapping != mapping)) {
continue_unlock:
unlock_page(page);
continue;
}
if (!PageDirty(page)) {
/* someone wrote it for us */
goto continue_unlock;
}
if (PageWriteback(page)) {
if (wbc->sync_mode != WB_SYNC_NONE)
wait_on_page_writeback(page);
else
goto continue_unlock;
}
BUG_ON(PageWriteback(page));
if (!clear_page_dirty_for_io(page))
goto continue_unlock;
ret = (*writepage)(page, wbc, data);
if (unlikely(ret)) {
if (ret == AOP_WRITEPAGE_ACTIVATE) {
unlock_page(page);
ret = 0;
} else {
/*
* done_index is set past this page,
* so media errors will not choke
* background writeout for the entire
* file. This has consequences for
* range_cyclic semantics (ie. it may
* not be suitable for data integrity
* writeout).
*/
done = 1;
break;
}
}
if (wbc->sync_mode == WB_SYNC_NONE) {
wbc->nr_to_write--;
if (wbc->nr_to_write <= 0) {
done = 1;
break;
}
}
if (wbc->nonblocking && bdi_write_congested(bdi)) {
wbc->encountered_congestion = 1;
done = 1;
break;
}
}
pagevec_release(&pvec);
cond_resched();
}
if (!cycled) {
/*
* range_cyclic:
* We hit the last page and there is more work to be done: wrap
* back to the start of the file
*/
cycled = 1;
index = 0;
end = writeback_index - 1;
goto retry;
}
if (!wbc->no_nrwrite_index_update) {
if (wbc->range_cyclic || (range_whole && nr_to_write > 0))
mapping->writeback_index = done_index;
wbc->nr_to_write = nr_to_write;
}
return ret;
}
EXPORT_SYMBOL(write_cache_pages);
/*
* Function used by generic_writepages to call the real writepage
* function and set the mapping flags on error
*/
static int __writepage(struct page *page, struct writeback_control *wbc,
void *data)
{
struct address_space *mapping = data;
int ret = mapping->a_ops->writepage(page, wbc);
mapping_set_error(mapping, ret);
return ret;
}
/**
* generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
* @mapping: address space structure to write
* @wbc: subtract the number of written pages from *@wbc->nr_to_write
*
* This is a library function, which implements the writepages()
* address_space_operation.
*/
int generic_writepages(struct address_space *mapping,
struct writeback_control *wbc)
{
/* deal with chardevs and other special file */
if (!mapping->a_ops->writepage)
return 0;
return write_cache_pages(mapping, wbc, __writepage, mapping);
}
EXPORT_SYMBOL(generic_writepages);
int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
{
int ret;
if (wbc->nr_to_write <= 0)
return 0;
wbc->for_writepages = 1;
if (mapping->a_ops->writepages)
ret = mapping->a_ops->writepages(mapping, wbc);
else
ret = generic_writepages(mapping, wbc);
wbc->for_writepages = 0;
return ret;
}
/**
* write_one_page - write out a single page and optionally wait on I/O
* @page: the page to write
* @wait: if true, wait on writeout
*
* The page must be locked by the caller and will be unlocked upon return.
*
* write_one_page() returns a negative error code if I/O failed.
*/
int write_one_page(struct page *page, int wait)
{
struct address_space *mapping = page->mapping;
int ret = 0;
struct writeback_control wbc = {
.sync_mode = WB_SYNC_ALL,
.nr_to_write = 1,
};
BUG_ON(!PageLocked(page));
if (wait)
wait_on_page_writeback(page);
if (clear_page_dirty_for_io(page)) {
page_cache_get(page);
ret = mapping->a_ops->writepage(page, &wbc);
if (ret == 0 && wait) {
wait_on_page_writeback(page);
if (PageError(page))
ret = -EIO;
}
page_cache_release(page);
} else {
unlock_page(page);
}
return ret;
}
EXPORT_SYMBOL(write_one_page);
/*
* For address_spaces which do not use buffers nor write back.
*/
int __set_page_dirty_no_writeback(struct page *page)
{
if (!PageDirty(page))
SetPageDirty(page);
return 0;
}
/*
* For address_spaces which do not use buffers. Just tag the page as dirty in
* its radix tree.
*
* This is also used when a single buffer is being dirtied: we want to set the
* page dirty in that case, but not all the buffers. This is a "bottom-up"
* dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
*
* Most callers have locked the page, which pins the address_space in memory.
* But zap_pte_range() does not lock the page, however in that case the
* mapping is pinned by the vma's ->vm_file reference.
*
* We take care to handle the case where the page was truncated from the
* mapping by re-checking page_mapping() inside tree_lock.
*/
int __set_page_dirty_nobuffers(struct page *page)
{
if (!TestSetPageDirty(page)) {
struct address_space *mapping = page_mapping(page);
struct address_space *mapping2;
if (!mapping)
return 1;
spin_lock_irq(&mapping->tree_lock);
mapping2 = page_mapping(page);
if (mapping2) { /* Race with truncate? */
BUG_ON(mapping2 != mapping);
WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
if (mapping_cap_account_dirty(mapping)) {
__inc_zone_page_state(page, NR_FILE_DIRTY);
__inc_bdi_stat(mapping->backing_dev_info,
BDI_RECLAIMABLE);
task_io_account_write(PAGE_CACHE_SIZE);
}
radix_tree_tag_set(&mapping->page_tree,
page_index(page), PAGECACHE_TAG_DIRTY);
}
spin_unlock_irq(&mapping->tree_lock);
if (mapping->host) {
/* !PageAnon && !swapper_space */
__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
}
return 1;
}
return 0;
}
EXPORT_SYMBOL(__set_page_dirty_nobuffers);
/*
* When a writepage implementation decides that it doesn't want to write this
* page for some reason, it should redirty the locked page via
* redirty_page_for_writepage() and it should then unlock the page and return 0
*/
int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
{
wbc->pages_skipped++;
return __set_page_dirty_nobuffers(page);
}
EXPORT_SYMBOL(redirty_page_for_writepage);
/*
* If the mapping doesn't provide a set_page_dirty a_op, then
* just fall through and assume that it wants buffer_heads.
*/
static int __set_page_dirty(struct page *page)
{
struct address_space *mapping = page_mapping(page);
if (likely(mapping)) {
int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
#ifdef CONFIG_BLOCK
if (!spd)
spd = __set_page_dirty_buffers;
#endif
return (*spd)(page);
}
if (!PageDirty(page)) {
if (!TestSetPageDirty(page))
return 1;
}
return 0;
}
int set_page_dirty(struct page *page)
{
int ret = __set_page_dirty(page);
if (ret)
task_dirty_inc(current);
return ret;
}
EXPORT_SYMBOL(set_page_dirty);
/*
* set_page_dirty() is racy if the caller has no reference against
* page->mapping->host, and if the page is unlocked. This is because another
* CPU could truncate the page off the mapping and then free the mapping.
*
* Usually, the page _is_ locked, or the caller is a user-space process which
* holds a reference on the inode by having an open file.
*
* In other cases, the page should be locked before running set_page_dirty().
*/
int set_page_dirty_lock(struct page *page)
{
int ret;
lock_page_nosync(page);
ret = set_page_dirty(page);
unlock_page(page);
return ret;
}
EXPORT_SYMBOL(set_page_dirty_lock);
/*
* Clear a page's dirty flag, while caring for dirty memory accounting.
* Returns true if the page was previously dirty.
*
* This is for preparing to put the page under writeout. We leave the page
* tagged as dirty in the radix tree so that a concurrent write-for-sync
* can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage
* implementation will run either set_page_writeback() or set_page_dirty(),
* at which stage we bring the page's dirty flag and radix-tree dirty tag
* back into sync.
*
* This incoherency between the page's dirty flag and radix-tree tag is
* unfortunate, but it only exists while the page is locked.
*/
int clear_page_dirty_for_io(struct page *page)
{
struct address_space *mapping = page_mapping(page);
BUG_ON(!PageLocked(page));
ClearPageReclaim(page);
if (mapping && mapping_cap_account_dirty(mapping)) {
/*
* Yes, Virginia, this is indeed insane.
*
* We use this sequence to make sure that
* (a) we account for dirty stats properly
* (b) we tell the low-level filesystem to
* mark the whole page dirty if it was
* dirty in a pagetable. Only to then
* (c) clean the page again and return 1 to
* cause the writeback.
*
* This way we avoid all nasty races with the
* dirty bit in multiple places and clearing
* them concurrently from different threads.
*
* Note! Normally the "set_page_dirty(page)"
* has no effect on the actual dirty bit - since
* that will already usually be set. But we
* need the side effects, and it can help us
* avoid races.
*
* We basically use the page "master dirty bit"
* as a serialization point for all the different
* threads doing their things.
*/
if (page_mkclean(page))
set_page_dirty(page);
/*
* We carefully synchronise fault handlers against
* installing a dirty pte and marking the page dirty
* at this point. We do this by having them hold the
* page lock at some point after installing their
* pte, but before marking the page dirty.
* Pages are always locked coming in here, so we get
* the desired exclusion. See mm/memory.c:do_wp_page()
* for more comments.
*/
if (TestClearPageDirty(page)) {
dec_zone_page_state(page, NR_FILE_DIRTY);
dec_bdi_stat(mapping->backing_dev_info,
BDI_RECLAIMABLE);
return 1;
}
return 0;
}
return TestClearPageDirty(page);
}
EXPORT_SYMBOL(clear_page_dirty_for_io);
int test_clear_page_writeback(struct page *page)
{
struct address_space *mapping = page_mapping(page);
int ret;
if (mapping) {
struct backing_dev_info *bdi = mapping->backing_dev_info;
unsigned long flags;
spin_lock_irqsave(&mapping->tree_lock, flags);
ret = TestClearPageWriteback(page);
if (ret) {
radix_tree_tag_clear(&mapping->page_tree,
page_index(page),
PAGECACHE_TAG_WRITEBACK);
if (bdi_cap_account_writeback(bdi)) {
__dec_bdi_stat(bdi, BDI_WRITEBACK);
__bdi_writeout_inc(bdi);
}
}
spin_unlock_irqrestore(&mapping->tree_lock, flags);
} else {
ret = TestClearPageWriteback(page);
}
if (ret)
dec_zone_page_state(page, NR_WRITEBACK);
return ret;
}
int test_set_page_writeback(struct page *page)
{
struct address_space *mapping = page_mapping(page);
int ret;
if (mapping) {
struct backing_dev_info *bdi = mapping->backing_dev_info;
unsigned long flags;
spin_lock_irqsave(&mapping->tree_lock, flags);
ret = TestSetPageWriteback(page);
if (!ret) {
radix_tree_tag_set(&mapping->page_tree,
page_index(page),
PAGECACHE_TAG_WRITEBACK);
if (bdi_cap_account_writeback(bdi))
__inc_bdi_stat(bdi, BDI_WRITEBACK);
}
if (!PageDirty(page))
radix_tree_tag_clear(&mapping->page_tree,
page_index(page),
PAGECACHE_TAG_DIRTY);
spin_unlock_irqrestore(&mapping->tree_lock, flags);
} else {
ret = TestSetPageWriteback(page);
}
if (!ret)
inc_zone_page_state(page, NR_WRITEBACK);
return ret;
}
EXPORT_SYMBOL(test_set_page_writeback);
/*
* Return true if any of the pages in the mapping are marked with the
* passed tag.
*/
int mapping_tagged(struct address_space *mapping, int tag)
{
int ret;
rcu_read_lock();
ret = radix_tree_tagged(&mapping->page_tree, tag);
rcu_read_unlock();
return ret;
}
EXPORT_SYMBOL(mapping_tagged);