linux-kernel - Re: [PATCH v7 2/2] mm: make lru_add_drain

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Message-ID: <20130814130526.GA28628@htj.dyndns.org>
Date:	Wed, 14 Aug 2013 09:05:26 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Chris Metcalf <cmetcalf@...era.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Cody P Schafer <cody@...ux.vnet.ibm.com>
Subject: Re: [PATCH v7 2/2] mm: make lru_add_drain_all() selective

Hello,

On Tue, Aug 13, 2013 at 11:46:29PM -0700, Andrew Morton wrote:
> What does "nest" mean?  lru_add_drain_all() calls itself recursively,
> presumably via some ghastly alloc_percpu()->alloc_pages(GFP_KERNEL)
> route?  If that ever happens then we'd certainly want to know about it.
> Hopefully PF_MEMALLOC would prevent infinite recursion.
> 
> If "nest" means something else then please enlighten me!
> 
> As for "doing it simultaneously", I assume we're referring to
> concurrent execution from separate threads.  If so, why would that "buy
> us anything"?  Confused.  As long as each thread sees "all pages which
> were in pagevecs at the time I called lru_add_drain_all() get spilled
> onto the LRU" then we're good.  afaict the implementation will do this.

I was wondering whether we can avoid all allocations by just
pre-allocating all resources.  If it can't call itself if we get rid
of all allocations && running multiple instances of them doesn't buy
us anything, the best solution would be allocating work items
statically and synchronize their use using a mutex.  That way the
whole thing wouldn't need any allocation.

Thanks.

-- 
tejun
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