zswap: fix writeback lock ordering for zsmalloc

Patch series "Implement writeback for zsmalloc", v7.

Unlike other zswap allocators such as zbud or z3fold, zsmalloc currently
lacks the writeback mechanism.  This means that when the zswap pool is
full, it will simply reject further allocations, and the pages will be
written directly to swap.

This series of patches implements writeback for zsmalloc. When the zswap
pool becomes full, zsmalloc will attempt to evict all the compressed
objects in the least-recently used zspages.


This patch (of 6):

zswap's customary lock order is tree->lock before pool->lock, because the
tree->lock protects the entries' refcount, and the free callbacks in the
backends acquire their respective pool locks to dispatch the backing
object.  zsmalloc's map callback takes the pool lock, so zswap must not
grab the tree->lock while a handle is mapped.  This currently only happens
during writeback, which isn't implemented for zsmalloc.  In preparation
for it, move the tree->lock section out of the mapped entry section

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Johannes Weiner <[email protected]>
Signed-off-by: Nhat Pham <[email protected]>
Reviewed-by: Sergey Senozhatsky <[email protected]>
Cc: Dan Streetman <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Nitin Gupta <[email protected]>
Cc: Seth Jennings <[email protected]>
Cc: Vitaly Wool <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions