linux-kernel - Re: [dm-devel] [PATCH] md/dm-ioctl.c: optimize memory allocation in copy

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Message-ID: <20140722020458.GE6822@agk-dp.fab.redhat.com>
Date:	Tue, 22 Jul 2014 03:04:58 +0100
From:	Alasdair G Kergon <agk@...hat.com>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Mikulas Patocka <mpatocka@...hat.com>,
	"xinhui.pan" <xinhuix.pan@...el.com>, linux-kernel@...r.kernel.org,
	agk@...hat.com, snitzer@...hat.com, dm-devel@...hat.com,
	"Liu, ShuoX" <shuox.liu@...el.com>
Subject: Re: [dm-devel] [PATCH] md/dm-ioctl.c: optimize memory allocation
	in copy_params

On Tue, Jul 22, 2014 at 02:23:52AM +0100, Alasdair G Kergon wrote:
> Unanswered.  Let's ask the same question in a different way:

A quick search for 'vold' returns:
  https://android.googlesource.com/platform/system/vold/
and the code there requests a fixed 64K allocation to hold the names of
active volumes.

So unlike libdevmapper-based applications where a smaller allocation is
used at first and only extended if needed, Android just assumes that
64KB is enough for everyone.

So is your claim that:

1. This 64KB allocation for the brief duration of the ioctl to store the
names of active device-mapper volumes leads to memory problems?
[Mustn't the system *already* be in a bad state if this pushes it over
the limit?]

and

2. The systems on which this memory shortage occurs have so many volumes
(with long names?) that a smaller allocation would not suffice?

Alasdair

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