mm: remove compressed copy from zram in-memory

Swap subsystem does lazy swap slot free with expecting the page
would be swapped out again so we can avoid unnecessary write.

But the problem in in-memory swap(ex, zram) is that it consumes
memory space until vm_swap_full(ie, used half of all of swap device)
condition meet. It could be bad if we use multiple swap device,
small in-memory swap and big storage swap or in-memory swap alone.

This patch makes swap subsystem free swap slot as soon as swap-read
is completed and make the swapcache page dirty so the page should
be written out the swap device to reclaim it.
It means we never lose it.

I tested this patch with kernel compile workload.

1. before

compile time : 9882.42
zram max wasted space by fragmentation: 13471881 byte
memory space consumed by zram: 174227456 byte
the number of slot free notify: 206684

2. after

compile time : 9653.90
zram max wasted space by fragmentation: 11805932 byte
memory space consumed by zram: 154001408 byte
the number of slot free notify: 426972

Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Seth Jennings <sjenning@xxxxxxxxxxxxxxxxxx>
Cc: Nitin Gupta <ngupta@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>
Cc: Shaohua Li <shli@xxxxxxxxxx>
Signed-off-by: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
ARM: implement optimized percpu variable access

From: Rob Herring <rob.herring@calxeda.com>

Use the previously unused TPIDRPRW register to store percpu offsets.
TPIDRPRW is only accessible in PL1, so it can only be used in the kernel.

This replaces 2 loads with a mrc instruction for each percpu variable
access. With hackbench, the performance improvement is 1.4% on Cortex-A9
(highbank). Taking an average of 30 runs of "hackbench -l 1000" yields:

Before: 6.2191
After: 6.1348

Will Deacon reported similar delta on v6 with 11MPCore.

The asm "memory" constraints are needed here to ensure the percpu offset
gets reloaded. Testing by Will found that this would not happen in
__schedule() which is a bit of a special case as preemption is disabled
but the execution can move cores.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Will Deacon <will.deacon@arm.com>
ARM: keep __my_cpu_offset consistent with generic one

Commit 14318efb(ARM: 7587/1: implement optimized percpu variable access)
introduces arm's __my_cpu_offset to optimize percpu vaiable access,
which really works well on hackbench, but will cause __my_cpu_offset
to return garbage value before it is initialized in cpu_init() called
by setup_arch, so accessing percpu variable before setup_arch may cause
kernel hang. But generic __my_cpu_offset always returns zero before
percpu area is brought up, and won't hang kernel.

So the patch tries to clear __my_cpu_offset on boot CPU early
to avoid boot hang.

At least now percpu variable is accessed by lockdep before
setup_arch(), and enabling CONFIG_LOCK_STAT or CONFIG_DEBUG_LOCKDEP
can trigger kernel hang.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Nicolas Pitre <nico@linaro.org>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Ming Lei <tom.leiming@gmail.com>