On 09/30/2015 05:46 PM, Vitaly Wool wrote:
On Wed, Sep 30, 2015 at 5:37 PM, Vlastimil Babka <vbabka@xxxxxxx> wrote:
On 09/25/2015 11:54 AM, Vitaly Wool wrote:
Hello Minchan,
the main use case where I see unacceptably long stalls in UI with
zsmalloc is switching between users in Android.
There is a way to automate user creation and switching between them so
the test I run both to get vmstat statistics and to profile stalls is
to create a user, switch to it and switch back. Each test cycle does
that 10 times, and all the results presented below are averages for 20
runs.
Kernel configurations used for testing:
(1): vanilla
(2): (1) plus "make SLUB atomic" patch [1]
(3): (1) with zbud instead of zsmalloc
(4): (2) with compaction defer logic mostly disabled
Disabling compaction deferring leads to less compaction stalls? That indeed
looks very weird and counter-intuitive. Also what's "mostly" disabled mean?
Not that I'm not surprised myself. However, this is how it goes.
Namely, I reverted the following patches:
- mm, compaction: defer each zone individually instead of preferred zone
Oh, I see. Then you didn't disable compaction defer logic, but made it
coarse again instead of per-zone. Which means that an allocation that
can be satisfied from Normal zone will use the Normal zone's deferred
state to decide whether to compact also DMA and DMA32 zones *within the
same allocation attempt*. So by reverting the patch you might indeed get
less compact_stall (and success+failure) counts, but each stall will try
to compact all three zones. With individual defer, some stall might be
just for DMA32, some just for Normal, and the total number might be
higher, but the compaction overhead should be better distributed among
all the attempts. Looking at your latencies, looks like that's working fine:
The UI is blocked after user switching for, average:
(1) 1.84 seconds
(2) 0.89 seconds
(3) 1.32 seconds
(4) 0.87 seconds
Average for (2) vs (4) is roughly the same, I would guess within noise.
The UI us blocked after user switching for, worst-case:
(1) 2.91
(2) 1.12
(3) 1.79
(4) 1.34
The worst case is actually worse without individual defer, because you
end up compacting all zones in each single stall. With individual defer,
there's a low probability of that happening.
- mm, compaction: embed migration mode in compact_control
This probably affects just THPs.
- mm, compaction: add per-zone migration pfn cache for async compaction
Hard to say what's the effect of this.
- mm: compaction: encapsulate defer reset logic
This is just code consolidation.
~vitaly
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>