mtdswap? [LWN.net]

mtdswap?

Posted Apr 1, 2011 14:51 UTC (Fri) by knobunc (subscriber, #4678)
Parent article: The 2.6.39 merge window concludes

Does the mtdswap mean that I can have a swap device on a SD card (e.g. in an Android phone)? And how does it differ from the normal swap stuff?

The patch adds the following conf help:

  Provides volatile block device driver on top of mtd partition
  suitable for swapping.  The mapping of written blocks is not saved.
  The driver provides wear leveling by storing erase counter into the
  OOB.

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mtdswap?

Posted Apr 2, 2011 15:35 UTC (Sat) by BenHutchings (subscriber, #37955) [Link]

No, you cannot treat an SD card as an MTD. The flash translation layer is implemented on the card itself and there is no (standard) way to bypass this.

mtdswap?

Posted Apr 2, 2011 17:48 UTC (Sat) by knobunc (subscriber, #4678) [Link]

Ah, rats. Thanks for the info.

mtdswap?

Posted Apr 3, 2011 1:20 UTC (Sun) by giraffedata (subscriber, #1954) [Link]

But why can't you use the SD card for swapping already? The whole point of that flash translation layer in the SD card is so Linux wouldn't need special code like this. Doesn't the SD card look to Linux like a disk drive?

I would be afraid to swap to an SD card because of the wear. These products are sold for things like storing photographs -- applications where a heavy user would be unlikely to write to the same block even twice in a day. Swapping would probably wear one out pretty quickly, with a pretty nasty failure mode.