zsmalloc: remove zspage isolation for migration

zsmalloc: remove zspage isolation for migration

zspage isolation for migration introduced additional exceptions to be
dealt with since the zspage was isolated from class list.  The reason why
I isolated zspage from class list was to prevent race between obj_malloc
and page migration via allocating zpage from the zspage further.  However,
it couldn't prevent object freeing from zspage so it needed corner case
handling.

This patch removes the whole mess.  Now, we are fine since class->lock and
zspage->lock can prevent the race.

Link: https://lkml.kernel.org/r/20211115185909.3949505-7-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>