mm: remove compressed copy from zram in-memory

Swap subsystem does lazy swap slot free with expecting the page would be
swapped out again so we can avoid unnecessary write.

But the problem in in-memory swap(ex, zram) is that it consumes memory
space until vm_swap_full(ie, used half of all of swap device) condition
meet.  It could be bad if we use multiple swap device, small in-memory
swap and big storage swap or in-memory swap alone.

This patch makes swap subsystem free swap slot as soon as swap-read is
completed and make the swapcache page dirty so the page should be
written out the swap device to reclaim it.  It means we never lose it.

I tested this patch with kernel compile workload.

1. before

   compile time : 9882.42
   zram max wasted space by fragmentation: 13471881 byte
   memory space consumed by zram: 174227456 byte
   the number of slot free notify: 206684

2. after

   compile time : 9653.90
   zram max wasted space by fragmentation: 11805932 byte
   memory space consumed by zram: 154001408 byte
   the number of slot free notify: 426972

[[email protected]: tweak comment text]
[[email protected]: fix BUG due to non-swapcache pages in end_swap_bio_read()]
[[email protected]: invert unlikely() test, augment comment, 80-col cleanup]
Signed-off-by: Dan Magenheimer <[email protected]>
Signed-off-by: Minchan Kim <[email protected]>
Signed-off-by: Artem Savkov <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Seth Jennings <[email protected]>
Cc: Nitin Gupta <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Shaohua Li <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions