Re: Discard support (was Re: [PATCH] swap: send callback when swapslot is freed)

[Mark Lord]

Alan Cox wrote:
> Flush barriers are nightmare for more than enterprise. You drive
> basically goes for a hike for a bit which trashes interactivity as well.
> If the device can't do trim and the like without a drain I don't see much
> point doing it at all, except maybe to wait for idle devices and run a
> filesystem managed background 'strimmer' thread to just weed out now idle
> blocks that have stayed idle - eg by adding an inode of all the deleted
> untrimmed blocks and giving it an irregular empty ?
..

Agreed.  And I believe Matthew also said something similar already.
TRIM for the current (only!) SSDs needs to be a "batched, once in a while"
operation, rather than something done continuously.

And ideally, "once in a while" might be once a day, or once we have more
than a significant percentage of the drive capacity ready for a TRIM.

It needs to batch a lot of stuff into a single TRIM,
and not do it very often at all.

Cheers
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