[dm-devel] Revert "dm space maps: don't reset space map allocation cursor when committing"

[luomeng]

Yes, ramdisk itself is a thinly provisioned device. But We can't 
restrict what disks users use. So if disk doesn't support discard, it 
will cause this problem.
在 2022/3/2 0:06, Edward Thornber 写道:
> I'm having trouble understanding your issue.  Does your ramdisk only 
> allocate backing memory on demand?  (ie. is the ramdisk itself a thinly 
> provisioned device?).  If so, not supporting discard seems to be the 
> problem.
> 
> Thinp makes no promises about where it will allocate your data.  If you 
> write a file, delete it, discard and then rewrite the file there is no 
> guarantee that the file will be written to the same location.
> 
> On Tue, Mar 1, 2022 at 2:08 PM luomeng <luomeng12 at huawei.com 
> <mailto:luomeng12 at huawei.com>> wrote:
> 
>     Because thin-pool is storage over-commitment, one of the following
>     scenarios exists: constantly create and delete file, then the search
>     doesn't hit the end of the metadata device, but ramdisk hits the end
>     (not support discard). So the cursor doesn't reset.
> 
>     在 2022/2/28 23:37, Mike Snitzer 写道:
>      > What you're saying doesn't make any sense.  Especially when you
>      > consider this last part of the commit message:
>      > "Fix these issues by leaving the cursor alone, only resetting
>     when the
>      >   search hits the end of the metadata device."
>