linux-kernel - Re: Distributed storage.

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Message-ID: <20070803134943.GA21221@2ka.mipt.ru>
Date:	Fri, 3 Aug 2007 17:49:44 +0400
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Daniel Phillips <phillips@...nq.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: Distributed storage.

On Fri, Aug 03, 2007 at 02:27:52PM +0200, Peter Zijlstra (peterz@...radead.org) wrote:
> On Fri, 2007-08-03 at 14:57 +0400, Evgeniy Polyakov wrote:
> 
> > For receiving situation is worse, since system does not know in advance
> > to which socket given packet will belong to, so it must allocate from
> > global pool (and thus there must be independent global reserve), and
> > then exchange part of the socket's reserve to the global one (or just
> > copy packet to the new one, allocated from socket's reseve is it was
> > setup, or drop it otherwise). Global independent reserve is what I
> > proposed when stopped to advertise network allocator, but it seems that
> > it was not taken into account, and reserve was always allocated only
> > when system has serious memory pressure in Peter's patches without any
> > meaning for per-socket reservation.
> 
> This is not true. I have a global reserve which is set-up a priori. You
> cannot allocate a reserve when under pressure, that does not make sense.

I probably did not cut enough details - my main position is to allocate
per socket reserve from socket's queue, and copy data there from main
reserve, all of which are allocated either in advance (global one) or
per sockoption, so that there would be no fairness issues what to mark 
as special and what to not.

Say we have a page per socket, each socket can assign a reserve for
itself from own memory, this accounts both tx and rx side. Tx is not
interesting, it is simple, rx has global reserve (always allocated on 
startup or sometime way before reclaim/oom)where data is originally 
received (including skb, shared info and whatever is needed, page is 
just an exmaple), then it is copied into per-socket reserve and reused 
for the next packet. Having per-socket reserve allows to have progress 
in any situation not only in cases where single action must be 
received/processed, and allows to be completely fair for all users, but
not only special sockets, thus admin for example would be allowed to
login, ipsec would work and so on...

-- 
	Evgeniy Polyakov
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