* [Drbd-dev] Re: question about drbd
[not found] ` <004101c6fca1$1593f4b0$04710a0a@jacobson>
@ 2006-11-02 8:57 ` Philipp Reisner
0 siblings, 0 replies; only message in thread
From: Philipp Reisner @ 2006-11-02 8:57 UTC (permalink / raw)
To: Jacobson; +Cc: drbd-dev
Am Dienstag, 31. Oktober 2006 05:00 schrieb Jacobson:
> Dear philipp:
> I am now studying drbd code. I can not get why, in function
> _drbd_send_page(), the page send method can not be used in case of
> PageSlab(page) == 1? I am looking forword to your response:). Many thanks.
> one of drbd fan
If I remeber correctly, pages that are controlled by slab have only a
use count of one (Slab holds that single reference) [maybe it was zero,
because slab does not use the reference counting on pages].
When zero copy send is done, the network code simply decreases the
reference count to that page by one.
I think it was the slab code that does not like it if someone
modifies the reference counts of the pages with are owned by
slab.
PS: As noted in the code, the only FS at that time, was XFS, which
was using such pages...
-Phil
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