Re: [PATCH 3/5] dm: support retrieving struct dm_target from struct dm_dev
From: YangYang
Date: Sun May 19 2024 - 23:13:19 EST
On 2024/5/17 22:33, Benjamin Marzinski wrote:
On Fri, May 17, 2024 at 03:48:49PM +0800, YangYang wrote:
On 2024/5/16 23:29, Benjamin Marzinski wrote:
On Thu, May 16, 2024 at 09:55:53AM +0800, YangYang wrote:
On 2024/5/15 23:42, Benjamin Marzinski wrote:
On Tue, May 14, 2024 at 05:04:42PM +0800, Yang Yang wrote:
If I understand correctly, you are suggesting to iterate through all the
targets, handling those with sends_pass_around_flush set, and skipping
those where sends_pass_around_flush is not set. I believe this approach
may result in some CPU wastage.
for i in {0..1023}; do
echo $((8000*$i)) 8000 linear /dev/sda2 $((16384*$i))
done | sudo dmsetup create example
In this specific scenario, a single iteration of the loop is all that
is needed.
It's just one iteration of the loop either way. You either loop through
the targets or the devices. It's true that if you have lots of targets
all mapped to the same device, you would waste time looping through all
the targets instead of looping through the devices. But if you only had
one striped target mapped to lots of devices, you would waste time
looping through all of the devices instead of looping through the
targets.
Yes, I get your point. This patchset may make things even worse for
the striped target.
I am just curious, in what scenario is the "dm-strip" target mapped to
a large number of underlying devices from the same block device.
I don't think anyone in the real world does create dm-stripe devices with a
huge number of stripe table devices. My point was that it didn't seem
obvious me that looping through the targets was a significant problem
compared to looping through the devices.
At any rate, Mikulas's patch already does this optimally, even for
targets like dm-stripe, so it doesn't really matter now.
-Ben
Yeah. Thanks for the explanation and your patience.