On 09/12/2013 09:09 PM, Fengguang Wu wrote:
On Fri, Sep 13, 2013 at 08:51:33AM +0800, Fengguang Wu wrote:
Hi Peter,
FYI, we noticed much increased vmap_area_lock contentions since this
commit:
commit 20bafb3d23d108bc0a896eb8b7c1501f4f649b77
Author: Peter Hurley <pe...@hurleysoftware.com>
Date: Sat Jun 15 10:21:19 2013 -0400
n_tty: Move buffers into n_tty_data
Reduce pointer reloading and improve locality-of-reference;
allocate read_buf and echo_buf within struct n_tty_data.
Here are some comparison between this commit [o] with its parent commit [*].
[...]
8cb06c983822103da1cf 20bafb3d23d108bc0a89
------------------------ ------------------------
976.67 +108.3% 2034.67
lkp-a04/micro/netperf/120s-200%-TCP_STREAM
8971.36 +11.4% 9997.05
nhm-white/micro/aim7/exec_test
9948.03 +20.9% 12031.72 TOTAL
slabinfo.kmalloc-128.active_objs
8cb06c983822103da1cf 20bafb3d23d108bc0a89
------------------------ ------------------------
976.67 +108.3% 2034.67
lkp-a04/micro/netperf/120s-200%-TCP_STREAM
9127.64 +11.4% 10164.15
nhm-white/micro/aim7/exec_test
10104.31 +20.7% 12198.82 TOTAL
slabinfo.kmalloc-128.num_objs
The dramatic increase in 128-byte kmalloc blocks is from vmalloc overhead
with associated with each allocation. On a x86_64, struct vmap_area is 104
bytes,
rounded to 128, allocated with every vmalloc allocation. This is approx 1%
overhead
(which seems high to me).
The reason this is still visible after the test completes is the vmap area is
lazily reclaimed (see mm/vmalloc.c:__purge_vmap_area_lazy()).
1% memory overhead coupled with the unwanted vmap_area_lock contention (even
though it is
test-induced) -- I might revert this anyway.
Regards,
Peter Hurley
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