Copy via mmap speed?

Asked Jan 19 '18 at 22:35

Active Jan 19 '18 at 22:35

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An answer to this question:

Can I do a copy-on-write memcpy in Linux?

suggests one can achieve copy-on-write of a bunch of memory by:

opening a file
mmap()'ing the source to a file
mmap()'ing the destination to the same file (with MAP_PRIVATE)

But this seems rather fishy w.r.t. speed. I'm sure the I/O costs you something; and maybe there's more unforeseen overhead other than page table work.

So, what can be said with certainty about the speed of this procedure (perhaps as a function of the Linux kernel version)?

asked Jan 19 '18 at 22:35

einpoklum

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There's no I/O, just copying memory pages and adjusting page tables. – Barmar Jan 19 '18 at 23:40
@Barmar: Well, you have to open a file on disk. You could say that's a "preprocessing step", I suppose. – einpoklum Jan 20 '18 at 06:05
Yes, I thought you were asking about I/O during the copying. – Barmar Jan 22 '18 at 04:21

Copy via mmap speed?

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