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From: Daniel Micay <danielmicay@gmail.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jason Evans <jasone@canonware.com>,
	Linux API <linux-api@vger.kernel.org>
Subject: Re: [PATCH v3] mm: add mremap flag for preserving the old mapping
Date: Thu, 02 Oct 2014 17:09:39 -0400	[thread overview]
Message-ID: <542DBF13.6000305@gmail.com> (raw)
In-Reply-To: <CALCETrVHgvhAN3neoOpJEk94uM7QKm2izZpp+=1UA6qieaQiTQ@mail.gmail.com>

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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.

Adding a vm_ops table to MAP_PRIVATE|MAP_ANONYMOUS mappings has a
significant performance impact. I haven't yet narrowed it down, but
there's at least one code path a check of `!vma->vm_ops` for the fast
path. One is for transparent huge page faults, so the performance impact
makes sense. I'll use a simpler implementation for now since the
requirements are very narrow / simple.


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      parent reply	other threads:[~2014-10-02 21:09 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-09-30  4:55 [PATCH v3] mm: add mremap flag for preserving the old mapping Daniel Micay
2014-09-30  4:55 ` Daniel Micay
     [not found] ` <1412052900-1722-1-git-send-email-danielmicay-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2014-09-30  5:53   ` Andy Lutomirski
2014-09-30  5:53     ` Andy Lutomirski
2014-09-30  5:53     ` Andy Lutomirski
2014-09-30  9:36     ` Daniel Micay
2014-09-30  9:36       ` Daniel Micay
2014-09-30 17:49       ` Andy Lutomirski
2014-09-30 17:49         ` Andy Lutomirski
2014-10-01  2:32         ` Daniel Micay
2014-10-01  2:32           ` Daniel Micay
2014-10-02 21:09         ` Daniel Micay [this message]

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