linux-kernel - Re: [PATCH] remove memory.limit v.s. memsw.limit comparison.

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Message-ID: <20090604083110.GD7504@balbir.in.ibm.com>
Date:	Thu, 4 Jun 2009 16:31:10 +0800
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>
Subject: Re: [PATCH] remove memory.limit v.s. memsw.limit comparison.

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-06-04 14:10:43]:

> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> 
> Removes memory.limit < memsw.limit at setting limit check completely.
> 
> The limitation "memory.limit <= memsw.limit" was added just because
> it seems sane ...if memory.limit > memsw.limit, only memsw.limit works.
> 
> But To implement this limitation, we needed to use private mutex and make
> the code a bit complated.
> As Nishimura pointed out, in real world, there are people who only want
> to use memsw.limit.
> 
> Then, this patch removes the check. user-land library or middleware can check
> this in userland easily if this really concerns.
> 
> And this is a good change to charge-and-reclaim.
> 
> Now, memory.limit is always checked before memsw.limit
> and it may do swap-out. But, if memory.limit == memsw.limit, swap-out is
> finally no help and hits memsw.limit again. So, let's allow the condition
> memory.limit > memsw.limit. Then we can skip unnecesary swap-out.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

We can't change behaviour this way without breaking userspace scripts,
API and code. What does it mean for people already using these
features? Does it break their workflow?

-- 
	Balbir
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