zswap: change zswap's default allocator to zsmalloc

Out of zswap's 3 allocators, zsmalloc is the clear superior in terms of
memory utilization, both in theory and as observed in practice, with its
high storage density and low internal fragmentation.  zsmalloc is also
more actively developed and maintained, since it is the allocator of
choice for zswap for many users, as well as the only allocator for zram.

A historical objection to the selection of zsmalloc as the default
allocator for zswap is its lack of writeback capability.  However, this
has changed, with the zsmalloc writeback patchset, and the subsequent
zswap LRU refactor.  With this, there is not a lot of good reasons to keep
zbud, an otherwise inferior allocator, as the default instead of zswap.

This patch changes the default allocator to zsmalloc.  The only exception
is on settings without MMU, in which case zbud will remain as the default.

Link: https://lkml.kernel.org/r/20230908235115.2943486-1-nphamcs@gmail.com
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Yosry Ahmed <yosryahmed@google.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/Kconfig b/mm/Kconfig
index 264a2df5ecf5b91a2883e4594bd7707219ca309c..45f2971ef642e681f8d3cd5f08d3bc64f2a274aa 100644 (file)
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -130,6 +130,7 @@ config ZSWAP_COMPRESSOR_DEFAULT
 choice
        prompt "Default allocator"
        depends on ZSWAP
+       default ZSWAP_ZPOOL_DEFAULT_ZSMALLOC if MMU
        default ZSWAP_ZPOOL_DEFAULT_ZBUD
        help
          Selects the default allocator for the compressed cache for