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[PATCH 3.18 38/42] bcache: correct cache_dirty_target in __update_writeback_rate()

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3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tang Junhui <tang.junhui@zte.com.cn>

commit a8394090a9129b40f9d90dcb7f4a49d60c727ca6 upstream.

__update_write_rate() uses a Proportion-Differentiation Controller
algorithm to control writeback rate. A dirty target number is used in
this PD controller to control writeback rate. A larger target number
will make the writeback rate smaller, on the versus, a smaller target
number will make the writeback rate larger.

bcache uses the following steps to calculate the target number,
1) cache_sectors = all-buckets-of-cache-set * buckets-size
2) cache_dirty_target = cache_sectors * cached-device-writeback_percent
3) target = cache_dirty_target *
(sectors-of-cached-device/sectors-of-all-cached-devices-of-this-cache-set)

The calculation at step 1) for cache_sectors is incorrect, which does
not consider dirty blocks occupied by flash only volume.

A flash only volume can be took as a bcache device without cached
device. All data sectors allocated for it are persistent on cache device
and marked dirty, they are not touched by bcache writeback and garbage
collection code. So data blocks of flash only volume should be ignore
when calculating cache_sectors of cache set.

Current code does not subtract dirty sectors of flash only volume, which
results a larger target number from the above 3 steps. And in sequence
the cache device's writeback rate is smaller then a correct value,
writeback speed is slower on all cached devices.

This patch fixes the incorrect slower writeback rate by subtracting
dirty sectors of flash only volumes in __update_writeback_rate().

(Commit log composed by Coly Li to pass checkpatch.pl checking)

Signed-off-by: Tang Junhui <tang.junhui@zte.com.cn>
Reviewed-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/md/bcache/writeback.c |    3 ++-
 drivers/md/bcache/writeback.h |   19 +++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -21,7 +21,8 @@
 static void __update_writeback_rate(struct cached_dev *dc)
 {
 	struct cache_set *c = dc->disk.c;
-	uint64_t cache_sectors = c->nbuckets * c->sb.bucket_size;
+	uint64_t cache_sectors = c->nbuckets * c->sb.bucket_size -
+				bcache_flash_devs_sectors_dirty(c);
 	uint64_t cache_dirty_target =
 		div_u64(cache_sectors * dc->writeback_percent, 100);
 
--- a/drivers/md/bcache/writeback.h
+++ b/drivers/md/bcache/writeback.h
@@ -14,6 +14,25 @@ static inline uint64_t bcache_dev_sector
 	return ret;
 }
 
+static inline uint64_t  bcache_flash_devs_sectors_dirty(struct cache_set *c)
+{
+	uint64_t i, ret = 0;
+
+	mutex_lock(&bch_register_lock);
+
+	for (i = 0; i < c->nr_uuids; i++) {
+		struct bcache_device *d = c->devices[i];
+
+		if (!d || !UUID_FLASH_ONLY(&c->uuids[i]))
+			continue;
+	   ret += bcache_dev_sectors_dirty(d);
+	}
+
+	mutex_unlock(&bch_register_lock);
+
+	return ret;
+}
+
 static inline unsigned offset_to_stripe(struct bcache_device *d,
 					uint64_t offset)
 {

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[PATCH 3.18 00/42] 3.18.72-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 11/42] [PATCH - RESEND] crypto: AF_ALG - remove SGL terminator indicator when  chaining Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 25/42] scsi: sg: use standard lists for sg_requests Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 03/42] Revert "net: phy: Correctly process PHY_HALTED in phy_stop_machine()" Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 42/42] mac80211: flush hw_roc_start work before cancelling the ROC Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 05/42] ipv6: fix memory leak with multiple tables during netns destruction Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 27/42] scsi: sg: factor out sg_fill_request_table() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 12/42] ext4: fix incorrect quotaoff if the quota feature is enabled Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 01/42] ipv6: accept 64k - 1 packet length in ip6_find_1stfragopt() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 21/42] scsi: zfcp: fix payload with full FCP_RSP IU in SCSI trace records Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 29/42] scsi: qla2xxx: Fix an integer overflow in sysfs code Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 08/42] [PATCH] Revert "usb: musb: fix tx fifo flush handling again" Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 16/42] skd: Avoid that module unloading triggers a use-after-free Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 30/42] ftrace: Fix selftest goto location on error Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 07/42] f2fs: check hot_data for roll-forward recovery Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 37/42] bcache: Fix leak of bdev reference Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 40/42] bcache: fix for gc and write-back race Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 39/42] bcache: Correct return value for sysfs attach errors Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 41/42] bcache: fix bch_hprint crash and improve output Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 33/42] PCI: shpchp: Enable bridge bus mastering if MSI is enabled Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 06/42] ipv6: fix typo in fib6_net_exit() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 31/42] tracing: Apply trace_clock changes to instance max buffer Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 38/42] bcache: correct cache_dirty_target in __update_writeback_rate() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 32/42] ARC: Re-enable MMU upon Machine Check exception Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 28/42] scsi: sg: fixup infoleak when using SG_GET_REQUEST_TABLE Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 34/42] media: v4l2-compat-ioctl32: Fix timespec conversion Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 04/42] tcp: initialize rcv_mss to TCP_MIN_MSS instead of 0 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 35/42] media: uvcvideo: Prevent heap overflow when accessing mapped controls Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 24/42] scsi: sg: remove save_scat_len Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 14/42] block: Relax a check in blk_start_queue() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 18/42] scsi: zfcp: fix queuecommand for scsi_eh commands when DIX enabled Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 22/42] scsi: zfcp: trace HBA FSF response by default on dismiss or timedout late response Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 26/42] scsi: sg: off by one in sg_ioctl() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 23/42] scsi: zfcp: trace high part of "new" 64 bit SCSI LUN Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 02/42] qlge: avoid memcpy buffer overflow Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 13/42] powerpc: Fix DAR reporting when alignment handler faults Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  Re: [PATCH 3.18 00/42] 3.18.72-stable review Guenter Roeck <linux@roeck-us.net> - 2017-09-25 03:10 +0200
    Re: [PATCH 3.18 00/42] 3.18.72-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-25 08:40 +0200
      Re: [PATCH 3.18 00/42] 3.18.72-stable review Guenter Roeck <linux@roeck-us.net> - 2017-09-25 13:10 +0200
        Re: [PATCH 3.18 00/42] 3.18.72-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-25 14:30 +0200
  Re: [PATCH 3.18 00/42] 3.18.72-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2017-09-26 01:20 +0200

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