Nigel Sandever <[EMAIL PROTECTED]> wrote:Only duplicating shared data on demand (COW) may work well on systems that support COW in the kernel.
No, we are dealing with VM objects and structures here - no kernel is involved for COWed copies of e.g. strings.
And also, COW at the OS level (that is, of memory pages) doesn't help, because we have complex data structures filled with pointers, so copying them involves more than just duplicating a block of memory. We can use an approach similar to what we do for strings to make a COW copy of, for instance, the globals stash, but overall that will only be a speed improvement if the data structure is rarely modified. (That is, once it's modified, we will have paid the price. Unless we have clever data structure which can be COWed in sections.)
Just adding to what Leo already said.
JEff
