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/*
* mm/page-writeback.c.
*
* Copyright (C) 2002, Linus Torvalds.
*
* Contains functions related to writing back dirty pages at the
* address_space level.
*
* 10Apr2002 akpm@zip.com.au
* 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/blkdev.h>
#include <linux/mpage.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>
/*
* The maximum number of pages to writeout in a single bdflush/kupdate
* operation. We do this so we don't hold I_LOCK 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;
static long total_pages; /* The total number of pages in the machine. */
static int dirty_exceeded; /* Dirty mem may be over limit */
/*
* 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 = 10;
/*
* The generator of dirty data starts writeback at this percentage
*/
int vm_dirty_ratio = 40;
/*
* The interval between `kupdate'-style writebacks, in centiseconds
* (hundredths of a second)
*/
int dirty_writeback_centisecs = 5 * 100;
/*
* The longest number of centiseconds for which data is allowed to remain dirty
*/
int dirty_expire_centisecs = 30 * 100;
/*
* Flag that makes the machine dump writes/reads and block dirtyings.
*/
int block_dump;
/*
* Flag that puts the machine in "laptop mode".
*/
int laptop_mode;
EXPORT_SYMBOL(laptop_mode);
/* End of sysctl-exported parameters */
static void background_writeout(unsigned long _min_pages);
struct writeback_state
{
unsigned long nr_dirty;
unsigned long nr_unstable;
unsigned long nr_mapped;
unsigned long nr_writeback;
};
static void get_writeback_state(struct writeback_state *wbs)
{
wbs->nr_dirty = read_page_state(nr_dirty);
wbs->nr_unstable = read_page_state(nr_unstable);
wbs->nr_mapped = read_page_state(nr_mapped);
wbs->nr_writeback = read_page_state(nr_writeback);
}
/*
* 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 void
get_dirty_limits(struct writeback_state *wbs, long *pbackground, long *pdirty,
struct address_space *mapping)
{
int background_ratio; /* Percentages */
int dirty_ratio;
int unmapped_ratio;
long background;
long dirty;
unsigned long available_memory = total_pages;
struct task_struct *tsk;
get_writeback_state(wbs);
#ifdef CONFIG_HIGHMEM
/*
* If this mapping can only allocate from low memory,
* we exclude high memory from our count.
*/
if (mapping && !(mapping_gfp_mask(mapping) & __GFP_HIGHMEM))
available_memory -= totalhigh_pages;
#endif
unmapped_ratio = 100 - (wbs->nr_mapped * 100) / total_pages;
dirty_ratio = vm_dirty_ratio;
if (dirty_ratio > unmapped_ratio / 2)
dirty_ratio = unmapped_ratio / 2;
if (dirty_ratio < 5)
dirty_ratio = 5;
background_ratio = dirty_background_ratio;
if (background_ratio >= dirty_ratio)
background_ratio = dirty_ratio / 2;
background = (background_ratio * available_memory) / 100;
dirty = (dirty_ratio * available_memory) / 100;
tsk = current;
if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
background += background / 4;
dirty += dirty / 4;
}
*pbackground = background;
*pdirty = 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)
{
struct writeback_state wbs;
long nr_reclaimable;
long background_thresh;
long dirty_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,
};
get_dirty_limits(&wbs, &background_thresh,
&dirty_thresh, mapping);
nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable;
if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
break;
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 (nr_reclaimable) {
writeback_inodes(&wbc);
get_dirty_limits(&wbs, &background_thresh,
&dirty_thresh, mapping);
nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable;
if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
break;
pages_written += write_chunk - wbc.nr_to_write;
if (pages_written >= write_chunk)
break; /* We've done our duty */
}
blk_congestion_wait(WRITE, HZ/10);
}
if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
dirty_exceeded<
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