linux-kernel - Re: [RFC][PATCH 1/7] Resource counters

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Date:	Tue, 13 Mar 2007 18:41:05 +0300
From:	Pavel Emelianov <xemul@...ru>
To:	Herbert Poetzl <herbert@...hfloor.at>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	containers@...ts.osdl.org, Paul Menage <menage@...gle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kirill Korotaev <dev@...ru>, Balbir Singh <balbir@...ibm.com>
Subject: Re: [RFC][PATCH 1/7] Resource counters

>>> PS: atomic_add_unless() didn't exist back then
>>> (at least I think so) but that might be an option
>>> too ...
>> I think as far as having this discussion if you can remove that race
>> people will be more willing to talk about what vserver does.
> 
> well, shouldn't be a big deal to brush that patch up
> (if somebody actually _is_ interested)
> 
>> That said anything that uses locks or atomic operations (finer grained
>> locks) because of the cache line ping pong is going to have scaling
>> issues on large boxes.
> 
> right, but atomic ops have much less impact on most
> architectures than locks :)

Right. But atomic_add_unless() is slower as it is
essentially a loop. See my previous letter in this sub-thread.

>> So in that sense anything short of per cpu variables sucks at scale.
>> That said I would much rather get a simple correct version without the
>> complexity of per cpu counters, before we optimize the counters that
>> much.
> 
> actually I thought about per cpu counters quite a lot, and
> we (Llinux-VServer) use them for accounting, but please
> tell me how you use per cpu structures for implementing 
> limits

Did you ever look at how get_empty_filp() works?
I agree, that this is not a "strict" limit, but it
limits the usage wit some "precision".

/* off-the-topic */ Herbert, you've lost Balbir again:
In this sub-thread some letters up Eric wrote a letter with
Balbir in Cc:. The next reply from you doesn't include him.
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