[RFC 0/3] make vm aware of zram-swap

[Minchan Kim <minchan@kernel.org>]

VM uses nr_swap_pages as one of information when it reclaims
anonymous page because nr_swap_pages means how many freeable
space in swap so VM is able to throttle swap out if it found
there is no more space in swap.

But for zram-swap, there is size gap between virtual disksize
and physical memory to be able to store compressed memory so
nr_swap_pages is not correct parameter to throttle swap.

It causes endless anonymous reclaim(ie, swapout) even if there
is no free space in zram-swap so it makes system unresponsive.

This patch adds new hint SWAP_GET_FREE so zram can return how
many of freeable space to VM. With using that, VM can know whether
zram is full and substract remained freeable space from
nr_swap_pages to make it less than 0. IOW, from now on, VM sees
there is no more space of zram so that it will stop anonymous
reclaiming until swap_entry_free free a page which increases
nr_swap_pages again.

With this patch, user will see OOM when zram-swap is full
instead of hang with no response.

Minchan Kim (3):
  zram: generalize swap_slot_free_notify
  mm: add swap_get_free hint for zram
  zram: add swap_get_free hint

 Documentation/filesystems/Locking |  7 ++----
 drivers/block/zram/zram_drv.c     | 36 +++++++++++++++++++++++++--
 include/linux/blkdev.h            |  8 ++++--
 mm/page_io.c                      |  7 +++---
 mm/swapfile.c                     | 52 +++++++++++++++++++++++++++++++++++----
 5 files changed, 93 insertions(+), 17 deletions(-)

-- 
2.0.0

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