Hi,
Here is my dd command:
dd if=/dev/zero of=/opt/laptop.bin bs=1G count=5 oflag=direct
The file system of /opt is XFS:
[root@localhost opt]# df -T | awk '{print $1,$2,$NF}' | grep "^/dev"
/dev/mapper/cl-root xfs /
/dev/sda1 xfs /boot
And this is virtual machine on my dektop so I just use it to test fio tool only and there is no read/write running process. And I don’t think there is no problem between virtual machine and physical machine.
I have also tested on 1 VM where I hosted using Virtuozzo. The page cache still increase.
Thank you very much.
Regards,
Son
-----Original Message-----
From: Sitsofe Wheeler [mailto:sitsofe@xxxxxxxxx]
Sent: Friday, April 21, 2017 1:33 PM
To: Son Chu <son.ct@xxxxxxxxxxxxx>
Cc: Srinivasa Chamarthy <chamarthy.raju@xxxxxxxxx>; fio@xxxxxxxxxxxxxxx
Subject: Re: Does fio really bypass page cache with option direct=1?
Hi,
Can you show the exact dd command (options, "of" and all) you used?
Also which filesystem is /opt/ running on and are you sure you're looking at the page cache just for the file you're writing (e.g. is something writing/reading elsewhere on the system at the same time if you're looking at the whole system page cache stats)?
On 21 April 2017 at 06:48, Son Chu <son.ct@xxxxxxxxxxxxx> wrote:
>
> I still got page cache increasing even when I used those option.
> Here is output without those option:
> fio --filename=/opt/test --size=1G --direct=1 --sync=1 --rw=randrw
> --bs=4k --numjobs=1 --iodepth=8 --runtime=60 --time_based --group_reporting --name=journal-test --invalidate=1 --gtod_reduce=1 --ioengine=libaio HITS MISSES DIRTIES RATIO BUFFERS_MB CACHE_MB
> 337 0 0 100.0% 0 95
> 411 0 89005 100.0% 0 664
> 337 0 38526 100.0% 0 816
> 337 0 26605 100.0% 0 920
> 591 0 19906 100.0% 0 998
> 337 0 12283 100.0% 0 1046
> 457 0 11351 100.0% 0 1090
> 337 0 12398 100.0% 0 1138
> 337 0 13252 100.0% 0 1190
> 337 0 11876 100.0% 0 1237
> 337 0 8723 100.0% 0 1271
> 337 0 12844 100.0% 0 1321
> 337 0 4612 100.0% 0 1340
> 457 0 0 100.0% 0 1340
> 337 0 3 100.0% 0 1340
> 457 0 0 100.0% 0 1340
> 457 0 0 100.0% 0 1340
> 337 0 0 100.0% 0 1340
> 336 1 0 99.7% 0 316
>
> And here is output with those option:
> fio --filename=/opt/test --size=1G --direct=1 --sync=1 --rw=randrw
> --bs=4k --numjobs=1 --iodepth=8 --runtime=60 --time_based --group_reporting --name=journal-test --invalidate=1 --gtod_reduce=1 --ioengine=libaio --create_on_open=1 --fallocate=none HITS MISSES DIRTIES RATIO BUFFERS_MB CACHE_MB
> 337 0 0 100.0% 0 95
> 337 0 0 100.0% 0 95
> 337 0 0 100.0% 0 95
> 410 1 0 99.8% 0 316
> 337 0 9 100.0% 0 316
> 337 0 0 100.0% 0 316
> 337 0 3 100.0% 0 316
> 337 0 0 100.0% 0 316
> 337 0 0 100.0% 0 316
> 1828 0 10 100.0% 0 316
> 337 0 0 100.0% 0 316
> 337 0 0 100.0% 0 316
> 337 0 0 100.0% 0 316
>
> As you can see the page cache still increase from 95 to 316 when using those option.
> I don't understand why the dd command with option oflag=direct gave no page cache increasing while fio increased page cache.
--
Sitsofe | http://sucs.org/~sits/
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