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Re: COPY_DELAY could perform worse than COPY_NONE

From: Samuel Thibault
Subject: Re: COPY_DELAY could perform worse than COPY_NONE
Date: Tue, 4 Oct 2011 10:06:12 +0200
User-agent: Mutt/1.5.21+34 (58baf7c9f32f) (2010-12-30)

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?


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