linux-kernel - Re: [PATCH resend] fs/proc: Move kfree outside pde_unload

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Date:	Thu, 4 Apr 2013 12:12:05 -0500
From:	Nathan Zimmer <nzimmer@....com>
To:	Al Viro <viro@...IV.linux.org.uk>
CC:	<akpm@...ux-foundation.org>, <linux-kernel@...r.kernel.org>,
	<linux-fsdevel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	David Woodhouse <dwmw2@...radead.org>, <stable@...r.kernel.org>
Subject: Re: [PATCH resend] fs/proc: Move kfree outside pde_unload_lock

On 04/04/2013 11:11 AM, Al Viro wrote:
> On Thu, Apr 04, 2013 at 10:53:39AM -0500, Nathan Zimmer wrote:
>> This moves a kfree outside a spinlock to help scaling on larger (512 core)
>> systems.  This should be some relief until we can move the section to use
>> the rcu.
> Umm...  That'll get wrecked as soon as fixes from #experimental go in;
> FWIW, I'd probably make close_pdeo() return pdeo or NULL, depending on
> whether we want it freed.  With kfree() itself taken to callers.
> But there's much bigger fish to fry there - turn use_pde() into
> return atomic_inc_unless_negative(&pde->pde_users), unuse_pde() into
> if (atomic_dec_return(&pde->pde_users) == BIAS) complete(pde->....)
> and make sure entry_rundown() sets completion *before* adding BIAS
> to pde_users and waits for it only if the sum was equal to BIAS.
> The spinlock is still needed, but only on the "now taking care of
> any pdeo that might still be around" side of things - it protects
> pdeo list.
>
> Again, see the last two commits of vfs.git#experimental.  I'd certainly
> appreciate any extra eyes on that sucker...
Ok I am cloning the tree now.
It does look like the patches would conflict.
I'll run some tests and take a deeper look.
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