linux-kernel - Re: [PATCH 3/5] x86: mm: Eliminate redundant page table walk during TLB range flushing

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Date:	Thu, 09 Jan 2014 14:49:35 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>, Alex Shi <alex.shi@...aro.org>,
	Ingo Molnar <mingo@...nel.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	H Peter Anvin <hpa@...or.com>, Linux-X86 <x86@...nel.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/5] x86: mm: Eliminate redundant page table walk during
 TLB range flushing

On 01/09/2014 09:34 AM, Mel Gorman wrote:
> When choosing between doing an address space or ranged flush, the x86
> implementation of flush_tlb_mm_range takes into account whether there are
> any large pages in the range. A per-page flush typically requires fewer
> entries than would covered by a single large page and the check is redundant.
>
> There is one potential exception. THP migration flushes single THP entries
> and it conceivably would benefit from flushing a single entry instead
> of the mm. However, this flush is after a THP allocation, copy and page
> table update potentially with any other threads serialised behind it. In
> comparison to that, the flush is noise. It makes more sense to optimise
> balancing to require fewer flushes than to optimise the flush itself.
>
> This patch deletes the redundant huge page check.
>
> Signed-off-by: Mel Gorman <mgorman@...e.de>

Reviewed-by: Rik van Riel <riel@...hat.com>

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