Re: [PATCH] Allow increasing the buffer-head per-CPU LRU size

From: Sebastien Buisson
Date: Tue Jul 08 2014 - 02:28:18 EST



Can anyone demonstrate why we shouldn't just do

I was assuming due to memory usage: with 4K blocks 32K->64K


Moreover, performance gain was not that satisfactory on ext4 when increasing BH_LRU_SIZE to 16.
Here are the performances I got with:
(a) mdtest on ramdisk device, single shared dir, with large ACL and SELinux
(b) mdtest on ramdisk device, single shared dir, with large ACL but NO SELinux

(results show performance gain in percentage when increasing BH_LRU_SIZE to 16)

(a)
files tasks dir size Creation Stat Removal
1000000 1 0 -8,7 -2,7 -0,5
1000000 1 100000 -5,2 -0,5 -1,1
1000000 1 500000 -5,1 -3,7 -1,5
1000000 1 2000000 -5,1 -4,0 -8,5
1000000 1 5000000 -4,2 -5,3 -10,2
1000000 1 10000000 -3,5 -8,0 -10,9
1000000 8 0 -0,3 -3,8 -1,2
1000000 8 100000 -1,2 -3,7 -1,5
1000000 8 500000 0,5 -3,2 -5,3
1000000 8 2000000 -1,7 -6,1 -8,7
1000000 8 5000000 -5,9 -7,7 -11,9
1000000 8 10000000 -4,1 -8,8 -13,6

(b)
files tasks dir size Creation Stat Removal
1000000 1 0 0,0 -0,9 -1,1
1000000 1 100000 1,0 -3,0 -3,5
1000000 1 500000 3,7 -3,0 -2,4
1000000 1 2000000 1,1 3,6 -0,2
1000000 1 5000000 3,5 0,1 5,9
1000000 1 10000000 9,0 3,8 6,4
1000000 8 0 2,4 -1,2 -4,3
1000000 8 100000 -0,2 -1,8 -2,4
1000000 8 500000 1,1 -0,3 2,0
1000000 8 2000000 -0,3 -2,8 -3,3
1000000 8 5000000 0,3 -3,1 -1,3
1000000 8 10000000 1,5 0,0 0,7


To compare with the performances I got on Lustre with:
(c) mds-survey on ramdisk device, quota enabled, shared directory
(d) mds-survey on ramdisk device, quota enabled, directory per process

(c)
fi dir threads create lookup destroy
1000000 1 1 11,3 1,2 7,2
1000000 1 2 6,4 2,3 6,9
1000000 1 4 1,9 3,0 1,3
1000000 1 8 -0,6 4,3 0,7
1000000 1 16 0,5 4,4 0,6

(d)
files dir threads create lookup destroy
1000000 4 4 3,2 28,5 5,3
1000000 8 8 1,2 33,9 2,0
1000000 16 16 0,6 7,9 -0,2


Sebastien.
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