Re: COPY_DELAY could perform worse than COPY_NONE

[Samuel Thibault]

Sergio López, le Tue 04 Oct 2011 09:54:55 +0200, a écrit :
> In objects where copy attribute is MEMORY_OBJECT_COPY_DELAY, for every
> read operation (usually done with vm_copy) all pages in the source
> object are write protected to be able to use copy-on-write
> optimizations. The cost for this operation seems to be higher than
> actually copying the pages for objects larger than just a bunch of
> pages. Moreover, this CoW optimization is lost for requests larger
> than 2k, since MiG stubs copy (with a conventional memcpy) the data
> from the buffer received in the message, to the actual address
> expected by the client.

I see. I guess it'll be the same for other FSes, and maybe
storeio/pager.c too?  Could you send a patch so that you show up as
author of the change?

Samuel