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

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Message-ID: <CA+55aFxhfkBDqVo+-rRHgkA4os7GkApvjNXW5SWXH03MW8Vw5A@mail.gmail.com>
Date:	Wed, 10 Jun 2015 09:42:34 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	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 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..)

                  Linus
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