linux-kernel - Re: [PATCH v3] mm: add mremap flag for preserving the old mapping

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Message-ID: <542B67C1.9080303@gmail.com>
Date:	Tue, 30 Sep 2014 22:32:33 -0400
From:	Daniel Micay <danielmicay@...il.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jason Evans <jasone@...onware.com>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH v3] mm: add mremap flag for preserving the old mapping

On 30/09/14 01:49 PM, Andy Lutomirski wrote:
> 
> I think it might pay to add an explicit vm_op to authorize
> duplication, especially for non-cow mappings.  IOW this kind of
> extension seems quite magical for anything that doesn't have the
> normal COW semantics, including for plain old read-only mappings.

This sounds like the best way forwards.

Setting up the op for private, anonymous mappings and having it check
vm_flags & VM_WRITE dynamically seems like it would be enough for the
intended use case in general purpose allocators. It can be extended to
other mapping types later if there's a compelling use case.
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