[linux-lvm] LVM2 modifies the buffer_head struct?

[Tom Walcott]

Hello,

Browsing the patch submitted for 2.4 inclusion, I noticed that LVM2 modifies 
the buffer_head struct. Why does LVM2 require the addition of it's own 
private field in the buffer_head? It seems that it should be able to use the 
existing b_private field.

How does that extra field affect performance relative to the cache? Won't 
any negative effects be seen by everything that uses buffer_heads? Also, as 
I understand the slab code and hardware cache alignment, won't the addition 
of the new field cause the each buffer_head to consume 128 bytes instead of 
96?

Just curious to know why this field was added, when the buffer_head already 
had a field for this purpose.

-Tom



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