On Tue 05-02-08 10:07:44, Al Boldi wrote:
quoted text > Jan Kara wrote:
> > On Sat 02-02-08 00:26:00, Al Boldi wrote:
> > > Chris Mason wrote:
> > > > Al, could you please compare the write throughput from vmstat for the
> > > > data=ordered vs data=writeback runs? I would guess the data=ordered
> > > > one has a lower overall write throughput.
> > >
> > > That's what I would have guessed, but it's actually going up 4x fold for
> > > mysql from 559mb to 2135mb, while the db-size ends up at 549mb.
> >
> > So you say we write 4-times as much data in ordered mode as in writeback
> > mode. Hmm, probably possible because we force all the dirty data to disk
> > when committing a transation in ordered mode (and don't do this in
> > writeback mode). So if the workload repeatedly dirties the whole DB, we
> > are going to write the whole DB several times in ordered mode but in
> > writeback mode we just keep the data in memory all the time. But this is
> > what you ask for if you mount in ordered mode so I wouldn't consider it a
> > bug.
>
> Ok, maybe not a bug, but a bit inefficient. Check out this workload:
>
> sync;
>
> while :; do
> dd < /dev/full > /mnt/sda2/x.dmp bs=1M count=20
> rm -f /mnt/sda2/x.dmp
> usleep 10000
> done
>
> vmstat 1 ( with mount /dev/sda2 /mnt/sda2 -o data=writeback) << note io-bo >>
>
> procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
> r b swpd free buff cache si so bi bo in cs us sy id wa
> 2 0 0 293008 5232 57436 0 0 0 0 18 206 4 80 16 0
> 1 0 0 282840 5232 67620 0 0 0 0 18 238 3 81 16 0
> 1 0 0 297032 5244 53364 0 0 0 152 21 211 4 79 17 0
> 1 0 0 285236 5244 65224 0 0 0 0 18 232 4 80 16 0
> 1 0 0 299464 5244 50880 0 0 0 0 18 222 4 80 16 0
> 1 0 0 290156 5244 60176 0 0 0 0 18 236 3 80 17 0
> 0 0 0 302124 5256 47788 0 0 0 152 21 213 4 80 16 0
> 1 0 0 292180 5256 58248 0 0 0 0 18 239 3 81 16 0
> 1 0 0 287452 5256 62444 0 0 0 0 18 202 3 80 17 0
> 1 0 0 293016 5256 57392 0 0 0 0 18 250 4 80 16 0
> 0 0 0 302052 5256 47788 0 0 0 0 19 194 3 81 16 0
> 1 0 0 297536 5268 52928 0 0 0 152 20 233 4 79 17 0
> 1 0 0 286468 5268 63872 0 0 0 0 18 212 3 81 16 0
> 1 0 0 301572 5268 48812 0 0 0 0 18 267 4 79 17 0
> 1 0 0 292636 5268 57776 0 0 0 0 18 208 4 80 16 0
> 1 0 0 302124 5280 47788 0 0 0 152 21 237 4 80 16 0
> 1 0 0 291436 5280 58976 0 0 0 0 18 205 3 81 16 0
> 1 0 0 302068 5280 47788 0 0 0 0 18 234 3 81 16 0
> 1 0 0 293008 5280 57388 0 0 0 0 18 221 4 79 17 0
> 1 0 0 297288 5292 52532 0 0 0 156 22 233 2 81 16 1
> 1 0 0 294676 5292 55724 0 0 0 0 19 199 3 81 16 0
>
>
> vmstat 1 (with mount /dev/sda2 /mnt/sda2 -o data=ordered)
>
> procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
> r b swpd free buff cache si so bi bo in cs us sy id wa
> 2 0 0 291052 5156 59016 0 0 0 0 19 223 3 82 15 0
> 1 0 0 291408 5156 58704 0 0 0 0 18 218 3 81 16 0
> 1 0 0 291888 5156 58276 0 0 0 20 23 229 3 80 17 0
> 1 0 0 300764 5168 49472 0 0 0 12864 91 235 3 69 13 15
> 1 0 0 300740 5168 49456 0 0 0 0 19 215 3 80 17 0
> 1 0 0 301088 5168 49044 0 0 0 0 18 241 4 80 16 0
> 1 0 0 298220 5168 51872 0 0 0 0 18 225 3 81 16 0
> 0 1 0 289168 5168 60752 0 0 0 12712 45 237 3 77 15 5
> 1 0 0 300260 5180 49852 0 0 0 152 68 211 4 72 15 9
> 1 0 0 298616 5180 51460 0 0 0 0 18 237 3 81 16 0
> 1 0 0 296988 5180 53092 0 0 0 0 18 223 3 81 16 0
> 1 0 0 296608 5180 53480 0 0 0 0 18 223 3 81 16 0
> 0 0 0 301640 5192 48036 0 0 0 12868 93 206 4 67 13 16
> 0 0 0 301624 5192 48036 0 0 0 0 21 218 3 81 16 0
> 0 0 0 301600 5192 48036 0 0 0 0 18 212 3 81 16 0
> 0 0 0 301584 5192 48036 0 0 0 0 18 209 4 80 16 0
> 0 0 0 301568 5192 48036 0 0 0 0 18 208 3 81 16 0
> 1 0 0 285520 5204 64548 0 0 0 12864 95 216 3 69 13 15
> 2 0 0 285124 5204 64924 0 0 0 0 18 222 4 80 16 0
> 1 0 0 283612 5204 66392 0 0 0 0 18 231 3 81 16 0
> 1 0 0 284216 5204 65736 0 0 0 0 18 218 4 80 16 0
> 0 1 0 289160 5204 60752 0 0 0 12712 56 213 3 74 15 8
> 1 0 0 285884 5216 64128 0 0 0 152 54 209 4 75 15 6
> 1 0 0 287472 5216 62572 0 0 0 0 18 223 3 81 16 0
>
> Do you think these 12mb redundant writeouts could be buffered?
No, I don't think so. At least when I run it, number of blocks written
out varies which confirms that these 12mb are just data blocks which happen
to be in the file when transaction commits (which is every 5 seconds). And
to satisfy journaling gurantees in ordered mode you must write them so you
really have no choice...
Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR
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