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Commit 16c4042f authored by Wu Fengguang's avatar Wu Fengguang Committed by Linus Torvalds
Browse files

writeback: avoid unnecessary calculation of bdi dirty thresholds 



Split get_dirty_limits() into global_dirty_limits()+bdi_dirty_limit(), so
that the latter can be avoided when under global dirty background
threshold (which is the normal state for most systems).

Signed-off-by: default avatarWu Fengguang <fengguang.wu@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e50e3720

fs/fs-writeback.c

+1 −1
Original line number Diff line number Diff line
@@ -590,7 +590,7 @@ static inline bool over_bground_thresh(void) 
{

	unsigned long background_thresh, dirty_thresh;



	get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);

	global_dirty_limits(&background_thresh, &dirty_thresh);



	return (global_page_state(NR_FILE_DIRTY) +

		global_page_state(NR_UNSTABLE_NFS) >= background_thresh);

include/linux/writeback.h

+3 −2
Original line number Diff line number Diff line
@@ -124,8 +124,9 @@ struct ctl_table; 
int dirty_writeback_centisecs_handler(struct ctl_table *, int,

				      void __user *, size_t *, loff_t *);



void get_dirty_limits(unsigned long *pbackground, unsigned long *pdirty,

		      unsigned long *pbdi_dirty, struct backing_dev_info *bdi);

void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty);

unsigned long bdi_dirty_limit(struct backing_dev_info *bdi,

			       unsigned long dirty);



void page_writeback_init(void);

void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,

mm/backing-dev.c

+2 −1
Original line number Diff line number Diff line
@@ -81,7 +81,8 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v) 
		nr_more_io++;

	spin_unlock(&inode_lock);



	get_dirty_limits(&background_thresh, &dirty_thresh, &bdi_thresh, bdi);

	global_dirty_limits(&background_thresh, &dirty_thresh);

	bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);



#define K(x) ((x) << (PAGE_SHIFT - 10))

	seq_printf(m,

mm/page-writeback.c

+38 −37
Original line number Diff line number Diff line
@@ -267,10 +267,11 @@ static inline void task_dirties_fraction(struct task_struct *tsk, 
 *

 *   dirty -= (dirty/8) * p_{t}

 */

static void task_dirty_limit(struct task_struct *tsk, unsigned long *pdirty)

static unsigned long task_dirty_limit(struct task_struct *tsk,

				       unsigned long bdi_dirty)

{

	long numerator, denominator;

	unsigned long dirty = *pdirty;

	unsigned long dirty = bdi_dirty;

	u64 inv = dirty >> 3;



	task_dirties_fraction(tsk, &numerator, &denominator);
@@ -278,10 +279,8 @@ static void task_dirty_limit(struct task_struct *tsk, unsigned long *pdirty) 
	do_div(inv, denominator);



	dirty -= inv;

	if (dirty < *pdirty/2)

		dirty = *pdirty/2;



	*pdirty = dirty;

	return max(dirty, bdi_dirty/2);

}



/*
@@ -391,9 +390,7 @@ unsigned long determine_dirtyable_memory(void) 
	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)

void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)

{

	unsigned long background;

	unsigned long dirty;
@@ -425,8 +422,11 @@ get_dirty_limits(unsigned long *pbackground, unsigned long *pdirty, 
	}

	*pbackground = background;

	*pdirty = dirty;

}



	if (bdi) {

unsigned long bdi_dirty_limit(struct backing_dev_info *bdi,

			       unsigned long dirty)

{

	u64 bdi_dirty;

	long numerator, denominator;
@@ -438,13 +438,12 @@ get_dirty_limits(unsigned long *pbackground, unsigned long *pdirty, 
	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;

		task_dirty_limit(current, pbdi_dirty);

	}

	return bdi_dirty;

}



/*
@@ -475,13 +474,24 @@ static void balance_dirty_pages(struct address_space *mapping, 
			.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);



		global_dirty_limits(&background_thresh, &dirty_thresh);



		/*

		 * 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;



		bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);

		bdi_thresh = task_dirty_limit(current, bdi_thresh);



		/*

		 * In order to avoid the stacked BDI deadlock we need

		 * to ensure we accurately count the 'dirty' pages when
@@ -513,15 +523,6 @@ static void balance_dirty_pages(struct address_space *mapping, 
		if (!dirty_exceeded)

			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;
@@ -634,7 +635,7 @@ void throttle_vm_writeout(gfp_t gfp_mask) 
	unsigned long dirty_thresh;



        for ( ; ; ) {

		get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);

		global_dirty_limits(&background_thresh, &dirty_thresh);



                /*

                 * Boost the allowable dirty threshold a bit for page