Re: [PATCH 1/2] fs: Do not dispatch FITRIM through separate super_operation

Mark Lord
2010-11-18T21:37:40Z

On 10-11-18 12:19 PM, James Bottomley wrote:
>
> Not stepping into the debate: I'm happy to see punch go to the mapping
> data and FITRIM pick it up later.
>
> However, I think it's time to question whether we actually still want to
> allow online discard at all. Most of the benchmarks show it to be a net
> lose to almost everything (either SSD or Thinly Provisioned arrays), so
> it's become an "enable this to degrade performance" option with no
> upside.

I also suspect that online TRIM exerts significant premature wear on the SSDs.
TRIM operations most likely trigger immediate copy/erase operations internal
to most SSDs, often regardless of the amount of data being trimmed.

Performing a 256KB erase because of a 1024-byte TRIM, over and over, is going
to harm the expected lifetime of an SSD. Sure, some SSDs may do things differently
internally, but I don't see it working that way in much of the current crop of SSDs.

Currently, I patch my kernels to remove the automatic online TRIMs.
Is there a knob somewhere for this in the later kernels?

Cheers