linux-kernel - Re: [PATCH 0/3] TLB flush multiple pages per IPI v5

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Date:	Wed, 10 Jun 2015 14:08:14 -0400
From:	Josh Boyer <jwboyer@...oraproject.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Dave Hansen <dave.hansen@...el.com>,
	Ingo Molnar <mingo@...nel.org>, Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Minchan Kim <minchan@...nel.org>,
	H Peter Anvin <hpa@...or.com>, Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 0/3] TLB flush multiple pages per IPI v5

On Wed, Jun 10, 2015 at 12:42 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Wed, Jun 10, 2015 at 9:17 AM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
>>
>> So anyway, I like the patch series. I just think that the final patch
>> - the one that actually saves the addreses, and limits things to
>> BATCH_TLBFLUSH_SIZE, should be limited.
>
> Oh, and another thing:
>
> Mel, can you please make that "struct tlbflush_unmap_batch" be just
> part of "struct task_struct" rather than a pointer?
>
> If you are worried about the cpumask size, you could use
>
>       cpumask_var_t cpumask;
>
> and
>
>         alloc_cpumask_var(..)
> ...
>         free_cpumask_var(..)
>
> for that.
>
> That way, sane configurations never have the allocation cost.
>
> (Of course, sad to say, sane configurations are probably few and far
> between. At least Fedora seems to ship with a kernel where NR_CPU's is
> 1024 and thus CONFIG_CPUMASK_OFFSTACK=y. Oh well. What a waste of CPU
> cycles that is..)

The insane part being NR_CPUS = 1024?  Or that to have said number
requires cpumask being dynamically allocated to avoid stack overflow?
(Or both I guess).

josh
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