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

[Sebastien Buisson]

> > 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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