mm: swap: enforce updating inuse_pages at the end of swap_range_free()

Patch series "mm: zswap: simplify zswap_swapoff()", v2.

These patches aim to simplify zswap_swapoff() by removing the unnecessary
trees cleanup code.  Patch 1 makes sure that the order of operations
during swapoff is enforced correctly, making sure the simplification in
patch 2 is correct in a future-proof manner.


This patch (of 2):

In swap_range_free(), we update inuse_pages then do some cleanups (arch
invalidation, zswap invalidation, swap cache cleanups, etc).  During
swapoff, try_to_unuse() checks that inuse_pages is 0 to make sure all swap
entries are freed.  Make sure we only update inuse_pages after we are done
with the cleanups in swap_range_free(), and use the proper memory barriers
to enforce it.  This makes sure that code following try_to_unuse() can
safely assume that swap_range_free() ran for all entries in thr swapfile
(e.g.  swap cache cleanup, zswap_swapoff()).

In practice, this currently isn't a problem because swap_range_free() is
called with the swap info lock held, and the swapoff code happens to spin
for that after try_to_unuse().  However, this seems fragile and
unintentional, so make it more relable and future-proof.  This also
facilitates a following simplification of zswap_swapoff().

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Yosry Ahmed <[email protected]>
Reviewed-by: "Huang, Ying" <[email protected]>
Cc: Chengming Zhou <[email protected]>
Cc: Chris Li <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Nhat Pham <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions