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Date: Fri, 7 Oct 2022 12:58:31 -0600
From: Jonathan Derrick <jonathan.derrick@...ux.dev>
To: Song Liu <song@...nel.org>
Cc: linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
jonathan.derrick@...idigm.com, jonathanx.sk.derrick@...el.com
Subject: Re: [PATCH 2/2] md/bitmap: Add chunk-count-based bitmap flushing
On 10/7/2022 11:50 AM, Song Liu wrote:
> On Thu, Oct 6, 2022 at 3:09 PM Jonathan Derrick
> <jonathan.derrick@...ux.dev> wrote:
>
> [...]
>
>> diff --git a/drivers/md/md-bitmap.h b/drivers/md/md-bitmap.h
>> index cfd7395de8fd..e0aeedbdde17 100644
>> --- a/drivers/md/md-bitmap.h
>> +++ b/drivers/md/md-bitmap.h
>> @@ -11,10 +11,12 @@
>> /* version 4 insists the bitmap is in little-endian order
>> * with version 3, it is host-endian which is non-portable
>> * Version 5 is currently set only for clustered devices
>> ++ * Version 6 supports the flush-chunks threshold
>> */
>> #define BITMAP_MAJOR_HI 4
>> #define BITMAP_MAJOR_CLUSTERED 5
>> #define BITMAP_MAJOR_HOSTENDIAN 3
>> +#define BITMAP_MAJOR_CHUNKFLUSH 6
>>
>> /*
>> * in-memory bitmap:
>> @@ -135,7 +137,8 @@ typedef struct bitmap_super_s {
>> * reserved for the bitmap. */
>> __le32 nodes; /* 68 the maximum number of nodes in cluster. */
>> __u8 cluster_name[64]; /* 72 cluster name to which this md belongs */
>> - __u8 pad[256 - 136]; /* set to zero */
>> + __le32 daemon_flush_chunks; /* 136 dirty chunks between flushes */
>> + __u8 pad[256 - 140]; /* set to zero */
>> } bitmap_super_t;
>
> Do we really need this to be persistent? How about we configure it at run
> time via a sysfs file?
>
> Also, please share more data on the performance benefit of the set.
>
> Thanks,
> Song
>
Hi Song,
Patch 1/2 changes default behavior, which patch 2/2 tries to address.
I can change it to be configurable via sysfs instead.
Should there be a default?
Here are my observations via biosnoop and RAID1, 4M chunksize, 238436 chunks, bitmap=internal
fio --name=test --direct=1 --filename=/dev/md0 --rw=randwrite --runtime=60
--percentile_list=1.0:25.0:50.0:75.0:90.0:95.0:99.0:99.9:99.99:99..999999:100.0
Default, bitmap updates happened concurrently with I/O:
bw ( KiB/s): min=18690, max=30618, per=99.94%, avg=23822.07, stdev=2522.73, samples=119
iops : min= 4672, max= 7654, avg=5955.20, stdev=630.71, samples=119
TIME(s) COMM PID DISK T SECTOR BYTES LAT(ms)
38.090366 md0_raid1 4800 nvme6n1 W 40 4096 0.01
38.090423 md0_raid1 4800 nvme3n1 W 40 4096 0.07
38.090442 md0_raid1 4800 nvme3n1 W 1016633184 4096 0.01
38.090439 md0_raid1 4800 nvme6n1 W 1016633184 4096 0.01
38.090479 md0_raid1 4800 nvme6n1 W 56 4096 0.01
38.090493 md0_raid1 4800 nvme6n1 W 1449894256 4096 0.01
38.090477 md0_raid1 4800 nvme3n1 W 56 4096 0.01
38.090496 md0_raid1 4800 nvme3n1 W 1449894256 4096 0.01
38.090530 md0_raid1 4800 nvme3n1 W 16 4096 0.01
38.090555 md0_raid1 4800 nvme3n1 W 110493568 4096 0.01
38.090538 md0_raid1 4800 nvme6n1 W 16 4096 0.01
38.090551 md0_raid1 4800 nvme6n1 W 110493568 4096 0.01
38.090596 md0_raid1 4800 nvme6n1 W 56 4096 0.01
38.090647 md0_raid1 4800 nvme3n1 W 56 4096 0.06
38.090666 md0_raid1 4800 nvme3n1 W 1455846976 4096 0.01
38.090663 md0_raid1 4800 nvme6n1 W 1455846976 4096 0.01
38.090707 md0_raid1 4800 nvme6n1 W 64 4096 0.01
38.090699 md0_raid1 4800 nvme3n1 W 64 4096 0.01
38.090723 md0_raid1 4800 nvme3n1 W 1665013728 4096 0.01
38.090720 md0_raid1 4800 nvme6n1 W 1665013728 4096 0.01
38.090764 md0_raid1 4800 nvme6n1 W 64 4096 0.01
38.090812 md0_raid1 4800 nvme3n1 W 64 4096 0.06
38.090832 md0_raid1 4800 nvme3n1 W 1637994296 4096 0.01
38.090828 md0_raid1 4800 nvme6n1 W 1637994296 4096 0.01
With patch 1/2, bitmaps only update on the 'delay' parameter (default 5s):
bw ( KiB/s): min=135712, max=230938, per=100.00%, avg=209308.56, stdev=29254.31, samples=119
iops : min=33928, max=57734, avg=52326.78, stdev=7313.57, samples=119
TIME(s) COMM PID DISK T SECTOR BYTES LAT(ms)
16.292235 md0_raid1 4841 nvme6n1 W 297367432 4096 0.01
16.292258 md0_raid1 4841 nvme6n1 W 16 4096 0.01
16.292266 md0_raid1 4841 nvme6n1 W 24 4096 0.01
16.292277 md0_raid1 4841 nvme6n1 W 32 4096 0.01
16.292259 md0_raid1 4841 nvme3n1 W 16 4096 0.01
16.292280 md0_raid1 4841 nvme3n1 W 32 4096 0.01
16.292305 md0_raid1 4841 nvme3n1 W 56 4096 0.01
16.292286 md0_raid1 4841 nvme6n1 W 40 4096 0.01
16.292295 md0_raid1 4841 nvme6n1 W 48 4096 0.01
16.292326 md0_raid1 4841 nvme3n1 W 72 1536 0.01
16.292323 md0_raid1 4841 nvme6n1 W 64 4096 0.02
16.292326 md0_raid1 4841 nvme6n1 W 56 4096 0.03
16.292334 md0_raid1 4841 nvme6n1 W 72 1536 0.02
16.300697 md0_raid1 4841 nvme3n1 W 1297533744 4096 0.01
16.300702 md0_raid1 4841 nvme6n1 W 1297533744 4096 0.01
16.300803 md0_raid1 4841 nvme6n1 W 1649080856 4096 0.01
16.300798 md0_raid1 4841 nvme3n1 W 1649080856 4096 0.01
16.300823 md0_raid1 4841 nvme3n1 W 1539317792 4096 0.01
16.300845 md0_raid1 4841 nvme3n1 W 1634570232 4096 0.01
16.300867 md0_raid1 4841 nvme3n1 W 579232208 4096 0.01
16.300889 md0_raid1 4841 nvme3n1 W 1818140424 4096 0.01
16.300922 md0_raid1 4841 nvme3n1 W 412971920 4096 0.02
...
21.293225 md0_raid1 4841 nvme3n1 W 1279122360 4096 0.01
21.293242 md0_raid1 4841 nvme3n1 W 40326272 4096 0.01
21.293223 md0_raid1 4841 nvme6n1 W 1279122360 4096 0.01
21.293243 md0_raid1 4841 nvme6n1 W 40326272 4096 0.01
21.293261 md0_raid1 4841 nvme6n1 W 16 4096 0.01
21.293266 md0_raid1 4841 nvme6n1 W 24 4096 0.01
21.293271 md0_raid1 4841 nvme6n1 W 32 4096 0.01
21.293275 md0_raid1 4841 nvme3n1 W 32 4096 0.01
21.293292 md0_raid1 4841 nvme3n1 W 48 4096 0.01
21.293296 md0_raid1 4841 nvme3n1 W 56 4096 0.01
21.293309 md0_raid1 4841 nvme3n1 W 72 1536 0.01
21.293266 md0_raid1 4841 nvme3n1 W 24 4096 0.01
21.293326 md0_raid1 4841 nvme6n1 W 48 4096 0.05
21.293328 md0_raid1 4841 nvme6n1 W 40 4096 0.06
21.293331 md0_raid1 4841 nvme6n1 W 72 1536 0.03
21.293333 md0_raid1 4841 nvme6n1 W 64 4096 0.04
21.293334 md0_raid1 4841 nvme6n1 W 56 4096 0.05
21.298526 md0_raid1 4841 nvme3n1 W 681973000 4096 0.01
Good, but with the granularity of N seconds, it might be too infrequent.
Here is chunk-flush=512 (2GB threshold in 4MB chunk size):
bw ( KiB/s): min=92692, max=134904, per=100.00%, avg=125127.43, stdev=6758.51, samples=119
iops : min=23173, max=33726, avg=31281.55, stdev=1689.63, samples=119
TIME(s) COMM PID DISK T SECTOR BYTES LAT(ms)
13.193339 md0_raid1 5972 nvme6n1 W 16 4096 0.01
13.193344 md0_raid1 5972 nvme6n1 W 32 4096 0.01
13.193346 md0_raid1 5972 nvme6n1 W 24 4096 0.01
13.193350 md0_raid1 5972 nvme6n1 W 40 4096 0.01
13.193356 md0_raid1 5972 nvme6n1 W 48 4096 0.01
13.193361 md0_raid1 5972 nvme6n1 W 64 4096 0.01
13.193363 md0_raid1 5972 nvme6n1 W 56 4096 0.01
13.193555 md0_raid1 5972 nvme6n1 W 72 1536 0.20
13.193289 md0_raid1 5972 nvme3n1 W 1912285848 4096 0.01
13.193306 md0_raid1 5972 nvme3n1 W 836455896 4096 0.01
13.193323 md0_raid1 5972 nvme3n1 W 233728136 4096 0.01
13.193339 md0_raid1 5972 nvme3n1 W 16 4096 0.01
13.193344 md0_raid1 5972 nvme3n1 W 24 4096 0.01
13.193362 md0_raid1 5972 nvme3n1 W 48 4096 0.01
13.193365 md0_raid1 5972 nvme3n1 W 64 4096 0.01
13.193366 md0_raid1 5972 nvme3n1 W 56 4096 0.01
13.193574 md0_raid1 5972 nvme3n1 W 72 1536 0.21
13.196759 md0_raid1 5972 nvme3n1 W 89571592 4096 0.01
13.196810 md0_raid1 5972 nvme6n1 W 89571592 4096 0.06
13.196913 md0_raid1 5972 nvme6n1 W 16 4096 0.01
13.196910 md0_raid1 5972 nvme3n1 W 16 4096 0.01
13.199444 md0_raid1 5972 nvme3n1 W 64 4096 0.01
13.199447 md0_raid1 5972 nvme3n1 W 137126232 4096 0.01
13.199515 md0_raid1 5972 nvme6n1 W 137126232 4096 0.08
13.199519 md0_raid1 5972 nvme6n1 W 64 4096 0.08
13.199617 md0_raid1 5972 nvme6n1 W 1216062808 4096 0.01
... (508 ios later)
13.208764 md0_raid1 5972 nvme6n1 W 16 4096 0.01
13.208768 md0_raid1 5972 nvme6n1 W 32 4096 0.01
13.208770 md0_raid1 5972 nvme6n1 W 24 4096 0.01
13.208775 md0_raid1 5972 nvme6n1 W 40 4096 0.01
13.208781 md0_raid1 5972 nvme6n1 W 48 4096 0.01
13.208786 md0_raid1 5972 nvme6n1 W 56 4096 0.01
13.208790 md0_raid1 5972 nvme6n1 W 64 4096 0.01
13.208729 md0_raid1 5972 nvme3n1 W 1607847808 4096 0.01
13.208747 md0_raid1 5972 nvme3n1 W 371214368 4096 0.01
13.208770 md0_raid1 5972 nvme3n1 W 32 4096 0.01
13.208789 md0_raid1 5972 nvme3n1 W 64 4096 0.01
13.208952 md0_raid1 5972 nvme6n1 W 72 1536 0.17
13.209079 md0_raid1 5972 nvme3n1 W 72 1536 0.29
13.212216 md0_raid1 5972 nvme3n1 W 1146106480 4096 0.01
13.212269 md0_raid1 5972 nvme6n1 W 1146106480 4096 0.06
13.212368 md0_raid1 5972 nvme6n1 W 16 4096 0.01
13.212365 md0_raid1 5972 nvme3n1 W 16 4096 0.01
Without 1/2: 6k iops
With 1/2: 52k iops
With 2/2 params as above: 31k iops
The count calculation could use some improvement to close the iops gap to delay-based flushing
>>
>> /* notes:
>> diff --git a/drivers/md/md.h b/drivers/md/md.h
>> index b4e2d8b87b61..d25574e46283 100644
>> --- a/drivers/md/md.h
>> +++ b/drivers/md/md.h
>> @@ -497,6 +497,7 @@ struct mddev {
>> struct mutex mutex;
>> unsigned long chunksize;
>> unsigned long daemon_sleep; /* how many jiffies between updates? */
>> + unsigned int daemon_flush_chunks; /* how many dirty chunks between updates */
>> unsigned long max_write_behind; /* write-behind mode */
>> int external;
>> int nodes; /* Maximum number of nodes in the cluster */
>> --
>> 2.31.1
>>
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