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Commit 8311c29d authored by NeilBrown's avatar NeilBrown Committed by Linus Torvalds
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md: reduce CPU wastage on idle md array with a write-intent bitmap 



On an md array with a write-intent bitmap, a thread wakes up every few seconds
and scans the bitmap looking for work to do.  If the array is idle, there will
be no work to do, but a lot of scanning is done to discover this.

So cache the fact that the bitmap is completely clean, and avoid scanning the
whole bitmap when the cache is known to be clean.

Signed-off-by: default avatarNeil Brown <neilb@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a35e63ef

drivers/md/bitmap.c

+17 −2
Original line number Original line Diff line number Diff line
@@ -1047,6 +1047,11 @@ void bitmap_daemon_work(struct bitmap *bitmap) 
	if (time_before(jiffies, bitmap->daemon_lastrun + bitmap->daemon_sleep*HZ))

	if (time_before(jiffies, bitmap->daemon_lastrun + bitmap->daemon_sleep*HZ))

		return;

		return;

	bitmap->daemon_lastrun = jiffies;

	bitmap->daemon_lastrun = jiffies;

	if (bitmap->allclean) {

		bitmap->mddev->thread->timeout = MAX_SCHEDULE_TIMEOUT;

		return;

	}

	bitmap->allclean = 1;





	for (j = 0; j < bitmap->chunks; j++) {

	for (j = 0; j < bitmap->chunks; j++) {

		bitmap_counter_t *bmc;

		bitmap_counter_t *bmc;
@@ -1068,8 +1073,10 @@ void bitmap_daemon_work(struct bitmap *bitmap) 
					clear_page_attr(bitmap, page, BITMAP_PAGE_NEEDWRITE);

					clear_page_attr(bitmap, page, BITMAP_PAGE_NEEDWRITE);





				spin_unlock_irqrestore(&bitmap->lock, flags);

				spin_unlock_irqrestore(&bitmap->lock, flags);

				if (need_write)

				if (need_write) {

					write_page(bitmap, page, 0);

					write_page(bitmap, page, 0);

					bitmap->allclean = 0;

				}

				continue;

				continue;

			}

			}
@@ -1098,6 +1105,9 @@ void bitmap_daemon_work(struct bitmap *bitmap) 
/*

/*

  if (j < 100) printk("bitmap: j=%lu, *bmc = 0x%x\n", j, *bmc);

  if (j < 100) printk("bitmap: j=%lu, *bmc = 0x%x\n", j, *bmc);

*/

*/

			if (*bmc)

				bitmap->allclean = 0;



			if (*bmc == 2) {

			if (*bmc == 2) {

				*bmc=1; /* maybe clear the bit next time */

				*bmc=1; /* maybe clear the bit next time */

				set_page_attr(bitmap, page, BITMAP_PAGE_CLEAN);

				set_page_attr(bitmap, page, BITMAP_PAGE_CLEAN);
@@ -1132,6 +1142,8 @@ void bitmap_daemon_work(struct bitmap *bitmap) 
		}

		}

	}

	}





	if (bitmap->allclean == 0)

		bitmap->mddev->thread->timeout = bitmap->daemon_sleep * HZ;

}

}





static bitmap_counter_t *bitmap_get_counter(struct bitmap *bitmap,

static bitmap_counter_t *bitmap_get_counter(struct bitmap *bitmap,
@@ -1226,6 +1238,7 @@ int bitmap_startwrite(struct bitmap *bitmap, sector_t offset, unsigned long sect 
			sectors -= blocks;

			sectors -= blocks;

		else sectors = 0;

		else sectors = 0;

	}

	}

	bitmap->allclean = 0;

	return 0;

	return 0;

}

}
@@ -1296,6 +1309,7 @@ int bitmap_start_sync(struct bitmap *bitmap, sector_t offset, int *blocks, 
		}

		}

	}

	}

	spin_unlock_irq(&bitmap->lock);

	spin_unlock_irq(&bitmap->lock);

	bitmap->allclean = 0;

	return rv;

	return rv;

}

}
@@ -1332,6 +1346,7 @@ void bitmap_end_sync(struct bitmap *bitmap, sector_t offset, int *blocks, int ab 
	}

	}

 unlock:

 unlock:

	spin_unlock_irqrestore(&bitmap->lock, flags);

	spin_unlock_irqrestore(&bitmap->lock, flags);

	bitmap->allclean = 0;

}

}





void bitmap_close_sync(struct bitmap *bitmap)

void bitmap_close_sync(struct bitmap *bitmap)
@@ -1399,7 +1414,7 @@ static void bitmap_set_memory_bits(struct bitmap *bitmap, sector_t offset, int n 
		set_page_attr(bitmap, page, BITMAP_PAGE_CLEAN);

		set_page_attr(bitmap, page, BITMAP_PAGE_CLEAN);

	}

	}

	spin_unlock_irq(&bitmap->lock);

	spin_unlock_irq(&bitmap->lock);



	bitmap->allclean = 0;

}

}





/* dirty the memory and file bits for bitmap chunks "s" to "e" */

/* dirty the memory and file bits for bitmap chunks "s" to "e" */

include/linux/raid/bitmap.h

+2 −0
Original line number Original line Diff line number Diff line
@@ -235,6 +235,8 @@ struct bitmap { 




	unsigned long flags;

	unsigned long flags;





	int allclean;



	unsigned long max_write_behind; /* write-behind mode */

	unsigned long max_write_behind; /* write-behind mode */

	atomic_t behind_writes;

	atomic_t behind_writes;