linux-kernel - Re: [PATCHSET v4 0/8] Make background writeback not suck

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Date:	Tue, 26 Apr 2016 09:07:32 -0600
From:	Jens Axboe <axboe@...com>
To:	<sedat.dilek@...il.com>
CC:	<linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
	<linux-block@...r.kernel.org>, <jack@...e.cz>,
	<dchinner@...hat.com>
Subject: Re: [PATCHSET v4 0/8] Make background writeback not suck

On 04/26/2016 01:04 AM, Sedat Dilek wrote:
> Hi Jens,
>
> I am testing current linux-block.git#wb-buf-throttle on top of Linux
> v4.6-rc5 here on my Ubuntu/precise AMD64.
> ( Was installed as a WUBI "test" system - "testing" since April 2012 :-) .)

Great! Thanks for testing.

> Here are some numbers:
>
> # df -T | egrep  'sda|loop'
> /dev/sda2      fuseblk  465546236 210981868 254564368   46% /host
> /dev/loop0     ext4      17753424  15586612   1241936   93% /
>
> # egrep 'sda|loop|ext4' /etc/fstab
> /host/ubuntu/disks/root.disk    /               ext4
> loop,errors=remount-ro  0       1
> /host/ubuntu/disks/swap.disk    none            swap    loop,sw
>           0       0

What kind of device is sda?

> ( Not sure why I cannot do a find on /sys/block/ .)

Probably the symlinks that confuse it.

> # find /sys/devices/ -name '*wb_stat*' | egrep 'loop0|sda'
> /sys/devices/pci0000:00/0000:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/block/sda/queue/wb_stats
> /sys/devices/virtual/block/loop0/queue/wb_stats
>
> # find /sys/devices/ -name '*wb_lat*' | egrep 'loop0|sda'
> /sys/devices/pci0000:00/0000:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/block/sda/queue/wb_lat_usec
> /sys/devices/virtual/block/loop0/queue/wb_lat_usec
>
> # cat /sys/devices/pci0000:00/0000:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/block/sda/queue/wb_stats
> /sys/devices/pci0000:00/0000:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/block/sda/queue/wb_lat_usec
> background=8, normal=16, max=31, inflight=0, wait=0, bdp_wait=0
> 75000
>
> # cat /sys/devices/virtual/block/loop0/queue/wb_stats
> /sys/devices/virtual/block/loop0/queue/wb_lat_usec
> background=16, normal=32, max=64, inflight=0, wait=0, bdp_wait=0
> 75000
>
> Questions...
>
> Planning a v5?

Yes, I'll post a v5 today or something like that. Functionally not a 
huge amount of changes, but it does have a few important bug fixes that 
make it perform better. The biggest part is making it generic, so it can 
be plugged into NFS as well, for instance.

> Will this go to Linux v4.7 or later?
> How should someone test?

Probably a bit too tight for 4.7, but one can always hope. 4.8 is 
probably a more realistic target.

Testing is really having some readers while you have writes going on. 
One example is doing something that reads while you have a dd writing to 
your device. Or interactive feel while installing a lot of packages, 
which tends to generate a ton of writes as well.

If you are so inclined, I'd encourage you to test the v5 I'll post later 
today. I've run that through the paces on various devices.

> Documentation...
>
> Can you add some more docs about getting infos (see above cat#s etc.)
> below Documentation/ directory?
> ( Talking about the stuff you have embedded in the commit-messages. )

Yeah, I'll do that, it is a bit light right now. It'll be in the next 
release.


-- 
Jens Axboe