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SubjectRe: vm-pageout-throttling.patch: hanging in throttle_vm_writeout/blk_congestion_wait
Hans Reiser <reiser@namesys.com> wrote:
>
> >>>loop-AES-2.2d)... I think (!) it caused this deadlock.
> >>>
> >>>
> >>That's not at all surprising. See the swap_extent work Andrew did
> >>for 2.5 (in mm/swapfile.c), by which swap to a swapfile now avoids
> >>the filesystem altogether (except while swapon prepares the map of
> >>disk blocks). By swapping to a loop device over a file, you're
> >>sneaking past his work, and putting the filesystem back under swap.
> >>
> >>
>
> Does Andrew's approach prevent putting swap on a compressed file (useful
> for reiser4 once the compression plugin is stable, not reiserfs)? (And
> no, I don't have any idea what the performance effect of that would be
> before it is tried and benchmarked....)

swapfiles bypass the filesystem completely, so if you're implementing
compression at the writepage() level, swap will cheerfully ignore all that
and will launch submit_bio() direct against your blockdev anyway.

encrypted swap should be done via dm-crypt. compressed swap would I guess
require dm-compress.
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