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From: Hugh Dickins <hugh@veritas.com>
To: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Miklos Szeredi <mszeredi@suse.cz>,
	Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	William Lee Irwin III <wli@holomorphy.com>,
	Nick Piggin <nickpiggin@yahoo.com.au>,
	Ingo Molnar <mingo@elte.hu>,
	linux-kernel@vger.kernel.org, Matt Helsley <matthltc@us.ibm.com>
Subject: Re: [PATCH] sys_remap_file_pages: fix ->vm_file accounting
Date: Wed, 6 Feb 2008 20:13:04 +0000 (GMT)	[thread overview]
Message-ID: <Pine.LNX.4.64.0802061957110.32204@blonde.site> (raw)
In-Reply-To: <20080203182952.GB5827@tv-sign.ru>

[ removed stable ]

On Sun, 3 Feb 2008, Oleg Nesterov wrote:
> Off-topic question to all. sys_remap_file_pages() doesn't work with
> shared readonly mappings, why?

Slight correction: it works with shared readonly mappings, doesn't
it, so long as the mmap'ed file was opened for reading and writing?

> IOW, why it checks VM_SHARED but not VM_MAYSHARE?

My guess has always been that it was just a misunderstanding of how
those VM_ flags end up working: assume so unless Ingo corrects me.

By the time I realized that oddity, we'd been driven into several
tiresome corners by the very existence of sys_remap_file_pages.
So whereas my usual instinct would have been to relax the restriction
and generalize, in its case I wanted to hold on to every restriction
we had.

sys_remap_file_pages does serve a useful purpose; but it subverts
vma principles, and has therefore caused us grief repeatedly.

Hugh

  reply	other threads:[~2008-02-06 20:14 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-01-30 14:20 Oleg Nesterov
2008-01-30 16:55 ` Miklos Szeredi
2008-01-30 17:26   ` Oleg Nesterov
2008-02-02 20:52     ` Matt Helsley
2008-02-02 21:17     ` Matt Helsley
2008-02-03 18:21       ` Oleg Nesterov
2008-02-06 20:33         ` Hugh Dickins
2008-02-07  0:16           ` Matt Helsley
2008-02-07 16:40             ` Hugh Dickins
2008-02-03 18:29     ` Oleg Nesterov
2008-02-06 20:13       ` Hugh Dickins [this message]
2008-02-11 10:15         ` Oleg Nesterov

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