Re: [gentoo-user] zram / compcache, anyone?

[Florian Philipp]

Am 14.10.2011 03:10, schrieb Pandu Poluan:
>
> On Oct 13, 2011 8:32 PM, "Florian Philipp" <lists@×××××××××××.net
> <mailto:lists@×××××××××××.net>> wrote:
>>
>> Am 13.10.2011 03:52, schrieb Pandu Poluan:
>> > Just stumbled upon this blog:
>> >
>> > http://www.webupd8.org/2011/10/increased-performance-in-linux-with.html
>> >
>> > anyone got any experience with zram/compcache on Gentoo?
>> >
[...]
>> I use it on my laptop (4GB RAM, typically 1-2GB swap used). It
>> works pretty well but I can't give you any hard figures.
>>
[...]
>> Only drawback so far: When zram is full, putting the laptop into standby
>> takes longer, maybe 15s compared to 3s without. Sometimes this can lead
>> to timeouts and the kernel aborts the suspend operation with an error on
>> dmesg. Reattempting it then succeeds.
>>
>
> Point taken. Do you think it's worth the slight annoyance?
>
> Rgds,
>

As a follow-up, this is what it looks like when suspend fails with full
zram:

PM: Syncing filesystems ... done.
PM: Preparing system for mem sleep
Freezing user space processes ... (elapsed 0.01 seconds) done.
Freezing remaining freezable tasks ...
Freezing of tasks failed after 20.00 seconds (1 tasks refusing to
freeze, wq_busy=0):
khugepaged      R  running task        0   522      2 0x00800000
 ffff88010255c600 ffff88010255c8b8 ffff88013602b7c0 ffffffff81026f33
 0000000000000000 00000000ffffffff ffff8800257ab308 ffff88013602b968
 ffff88013602b7e0 ffffffff81025d00 ffffea0000e8d378 0000000000000008
Call Trace:
 [<ffffffff81025d00>] ? ptep_clear_flush_young+0x20/0x30
 [<ffffffff810a6d18>] ? __pagevec_free+0x38/0x50
 [<ffffffff810ad4fc>] ? free_page_list+0xfc/0x110
 [<ffffffff810adabd>] ? shrink_page_list+0x14d/0x5e0
 [<ffffffff810ac40f>] ? isolate_lru_pages+0x19f/0x2b0
 [<ffffffff810ae4a9>] ? shrink_inactive_list+0x2c9/0x350
 [<ffffffff810a8f25>] ? determine_dirtyable_memory+0x15/0x30
 [<ffffffff810a8fce>] ? global_dirty_limits+0x2e/0x110
 [<ffffffff810a90eb>] ? throttle_vm_writeout+0x3b/0xa0
 [<ffffffff810aebf0>] ? shrink_zone+0x480/0x550
 [<ffffffff812a3a29>] ? i915_gem_inactive_shrink+0x169/0x1f0
 [<ffffffff81061d5c>] ? ktime_get_ts+0xac/0xe0
 [<ffffffff81093aa0>] ? delayacct_end+0x80/0xa0
 [<ffffffff810a429a>] ? zone_watermark_ok+0x1a/0x20
 [<ffffffff813e7fff>] ? schedule+0x8ef/0xae0
 [<ffffffff810a5af0>] ? page_alloc_cpu_notify+0x50/0x50
 [<ffffffff810a5b01>] ? drain_local_pages+0x11/0x20
 [<ffffffff810a7bd9>] ? __alloc_pages_nodemask+0x4e9/0x830
 [<ffffffff813e884d>] ? schedule_timeout+0x16d/0x260
 [<ffffffff81049bb0>] ? del_timer+0xa0/0xa0
 [<ffffffff813e8999>] ? schedule_timeout_interruptible+0x19/0x20
 [<ffffffff810db8f7>] ? khugepaged_alloc_hugepage+0xc7/0xf0
 [<ffffffff81059260>] ? wake_up_bit+0x40/0x40
 [<ffffffff810dbd0d>] ? khugepaged+0x8d/0x11f0
 [<ffffffff81059260>] ? wake_up_bit+0x40/0x40
 [<ffffffff810dbc80>] ? collect_mm_slot+0xa0/0xa0
 [<ffffffff81058df6>] ? kthread+0x96/0xa0
 [<ffffffff813ebb54>] ? kernel_thread_helper+0x4/0x10
 [<ffffffff81058d60>] ? kthread_worker_fn+0x180/0x180
 [<ffffffff813ebb50>] ? gs_change+0xb/0xb

Restarting tasks ... done

All things considered, I think it is worth it. This is my memory usage:
free -m
      total         used free shared buffers cached
Mem:  3753          3167  586      0      16    644
-/+ buffers/cache:  2505 1247
Swap: 8018          1487 6530

cat /proc/swaps
Filename   Type      Size    Used    Priority
/dev/zram0 partition 1921700 1520320 1
/dev/sda7  partition 6289412    2968 0

There is no observable slowdown, no swapping, no system freeze when
switching active windows. It feels like the system didn't swap at all. I
even increased swappiness to use more space for caching.

Regards,
Florian Philipp