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SubjectRe: [patch] Re: 2.3.42 buffer problem/leak ?
On Feb 09, Andrea Arcangeli wrote:

> Harald could you give a try to 2.3.42aa3?
>
> ftp://ftp.*.kernel.org/pub/linux/kernel/people/andrea/kerenls/v2.3/2.3.42aa3.gz
>
> The interesting bit is here:
>
> ftp://ftp.*.kernel.org/pub/linux/kernel/people/andrea/kernels/v2.3/2.3.42aa3/icache-dcache-preshrink-1.gz
>
> I attach the interesting patch to the email too. It's against 2.3.42.
>
> It basically avoids the caching part of the icache and dcache to grow more
> than 2% of the memory in the machine. You can tune via sysctl the
> percentage. The percentage should choosed in function of the hashtable
> size to avoid an insane number of collisions in the hash that could lead
> the dcache to be potentially slower than rereading the inode and direntry
> from the buffer cache. Actually the hashtable is not yet dynamic but of
> course my thoughts will apply to the future.

thanks for attaching the patch! while in theory I would agree with Linus
that fixed limits are not the best way to go, I've run some tests
and (at least for me) interesting results:

the problem with icache and dcache filling memory is triggered through
a nightly cron job running `updatedb' and `du' on all file systems
and showed up when compiling large sources (XFree86 or kernel) where
the memory isn't reused for buffer cache.
so I tried and timed the following sequence after reboot (without X11
or other running tasks) on K6/2-400 with 128MB and two old/slow SCSI disks
(4GB 7200rpm 6MB/sec and 2GB 5400rpm 4MB/sec), most fs space is e2fs
with 1k blocks, for some slabdata info see below (times are real/user/system
in min (m) and secs)

time updatedb
time du /
time updatedb
time du /
make clean
time make bzImage modules (2.3.42 sources with gcc-2.95.2)

for 2.2.14, 2.3.39, pristine 2.3.42 and 2.3.42 plus your patch:

2.2.14:
updatedb(1) 10m25r 51u 29s
du(1) 3m38r 9u 24s
updatedb(2) 3m00r 49u 27s
du(2) 3m17r 9u 23s
make 17m46r 977u 62s

2.3.39:
updatedb(1) 11m49r
du(1) 11m22r
updatedb(2)
du(2)
make 18m55r 980u 67s

2.3.42:
updatedb(1) 11m52r 50u 26s
du(1) 11m12r 9u 24s
updatedb(2) 12m30r 30u 30s
du(2) 11m23r 9u 26s
make 18m53r 979u 68s

2.3.42+patch:
updatedb(1) 10m40r 50u 31s
du(1) 1m40r 8u 17s
updatedb(2) 9m16r 50u 31s
du(2) 3117r 8u 17s
make 18m29r 980u 66s


observations:

- 2.3.39 and 2.3.42 behave the same way (true for slabdata information below, too).
- 2.2.14 du is _much_ faster than 2.3.42 without patch
- Andrea's patch made du much faster than even 2.2.14
- kernel compilation with 2.3.42+patch is better, but 2.2.14 is still ahead
- 2.2.14 updatedb for 2nd run is _much_ faster == cached, Andrea's patch
only gives a small step in that direction




and here the output of free and slabinfo first after updatedb and du,
then after kernel compile:

clean 2.3.42:
===============================================================================
total used free shared buffers cached
Mem: 126596 115124 11472 0 2136 10028
-/+ buffers/cache: 102960 23636
Swap: 82364 2464 79900
inode_cache 214738 227496
dentry_cache 113672 166036
buffer_head 9196 9198
size-32 4297 4347
-------------------------------------------------------------------------------
total used free shared buffers cached
Mem: 126596 121924 4672 0 1120 22476
-/+ buffers/cache: 98328 28268
Swap: 82364 2592 79772
inode_cache 173888 212064
dentry_cache 82951 164951
buffer_head 19314 19320
size-32 3606 4284
===============================================================================

2.3.42+patch
===============================================================================
total used free shared buffers cached
Mem: 126596 120028 6568 0 76060 13816
-/+ buffers/cache: 30152 96444
Swap: 82364 0 82364
buffer_head 89970 92400
inode_cache 27942 33204
dentry_cache 20310 25916
size-32 1823 1953
-------------------------------------------------------------------------------
total used free shared buffers cached
Mem: 126596 119416 7180 0 75744 13556
-/+ buffers/cache: 30116 96480
Swap: 82364 0 82364
buffer_head 89334 92778
inode_cache 28737 33192
dentry_cache 21063 25730
size-32 1824 1953
===============================================================================

2.3.39:
===============================================================================
total used free shared buffers cached
Mem: 126624 120804 5820 0 2408 7196
-/+ buffers/cache: 111200 15424
Swap: 82364 1088 81276
inode_cache 248914 248928
dentry_cache 145545 155806
buffer_head 8561 12138
size-32 4258 4284
-------------------------------------------------------------------------------
total used free shared buffers cached
Mem: 126624 122800 3824 0 1204 24956
-/+ buffers/cache: 96640 29984
Swap: 82364 1240 81124
inode_cache 188034 203556
dentry_cache 90865 155062
buffer_head 21687 21714
size-32 3766 4347
===============================================================================

2.2.14:
===============================================================================
total used free shared buffers cached
Mem: 128216 117596 10620 4044 89500 7488
-/+ buffers/cache: 20608 107608
Swap: 82364 3632 78732
buffer_head 92800 92946
dentry_cache 13906 16740
size-32 603 10206
vm_area_struct 504 630
-------------------------------------------------------------------------------
===============================================================================

Harald
--
All SCSI disks will from now on ___ _____
be required to send an email notice 0--,| /OOOOOOO\
24 hours prior to complete hardware failure! <_/ / /OOOOOOOOOOO\
\ \/OOOOOOOOOOOOOOO\
\ OOOOOOOOOOOOOOOOO|//
Harald Koenig, \/\/\/\/\/\/\/\/\/
Inst.f.Theoret.Astrophysik // / \\ \
koenig@tat.physik.uni-tuebingen.de ^^^^^ ^^^^^
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