On Tue, 15 Oct 2019, Hannes Reinecke wrote: > On 10/15/19 1:35 PM, Matthew Wilcox wrote: > > On Tue, Oct 15, 2019 at 01:38:27PM +0900, Naohiro Aota wrote: > >> A zoned block device consists of a number of zones. Zones are > >> either conventional and accepting random writes or sequential and > >> requiring that writes be issued in LBA order from each zone write > >> pointer position. For the write restriction, zoned block devices are > >> not suitable for a swap device. Disallow swapon on them. > > > > That's unfortunate. I wonder what it would take to make the swap code be > > suitable for zoned devices. It might even perform better on conventional > > drives since swapout would be a large linear write. Swapin would be a > > fragmented, seeky set of reads, but this would seem like an excellent > > university project. > > > The main problem I'm seeing is the eviction of pages from swap. > While swapin is easy (as you can do random access on reads), evict pages > from cache becomes extremely tricky as you can only delete entire zones. > So how to we mark pages within zones as being stale? > Or can we modify the swapin code to always swap in an entire zone and > discard it immediately? On swapout you would change the block number on the swap device to the latest and increment it? Mark the prio block number as unused and then at some convenient time scan the map and see if you can somehow free up a zone?
