linux-kernel - Re: increased vmap_area_lock contentions on "n_tty: Move buffers into n_tty

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Message-Id: <20130926110551.52ad8156.akpm@linux-foundation.org>
Date:	Thu, 26 Sep 2013 11:05:51 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>, lkp@...org,
	Tejun Heo <tj@...nel.org>
Subject: Re: increased vmap_area_lock contentions on
 "n_tty: Move buffers into n_tty_data"

On Thu, 26 Sep 2013 13:35:32 -0400 Peter Hurley <peter@...leysoftware.com> wrote:

> The issue with a single large kmalloc is that it may fail where
> 3 separate, page-or-less kmallocs would not have.

Or vmalloc fails first, because of internal fragmentation of the vmap
arena.  This problem plus vmalloc's slowness are the reasons why
vmalloc should be avoided.

A tremendous number of places in the kernel perform higher-order
allocations nowadays.  The page allocator works damn hard to service
them and I expect that switching to kmalloc here will be OK.
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