linux-kernel - Re: remap_file

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Message-ID: <20160215221748.GB35514@black.fi.intel.com>
Date:	Tue, 16 Feb 2016 01:17:48 +0300
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Grazvydas Ignotas <notasas@...il.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: remap_file_pages regression

On Tue, Feb 16, 2016 at 12:08:34AM +0200, Grazvydas Ignotas wrote:
> On Mon, Feb 15, 2016 at 12:26 PM, Kirill A. Shutemov
> <kirill.shutemov@...ux.intel.com> wrote:
> > On Mon, Feb 15, 2016 at 03:32:55AM +0200, Grazvydas Ignotas wrote:
> >> Hi,
> >>
> >> since remap_file_pages() rework the following simple program fails.
> >> I haven't actually bisected this, only know it worked on 3.19 at least
> >> (I bought a new system now and need 4.2+ for hardware support).
> >
> > The patch below should fix the issue. Please test.
> 
> It works, thanks.
> Tested-by: Grazvydas Ignotas <notasas@...il.com>
> 
> >
> >> If you are curious, the program is an emulator and is using
> >> remap_file_pages() to implement memory mirroring efficiently (and to
> >> remap things during run time).
> >
> > Could you elaborate on this?
> >
> > Why creating file on tmpfs/shmem (using memfd_create() for example) plus
> > plain mmap()s wouldn't work for you?
> 
> It works, but remap_file_pages() is just more convenient, you don't
> need many mmap()/munmap() calls (less syscalls)

mmap(MAP_FIXED) would do munmap() for you.

> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> 
> Cc: stable?
> Fixes: c8d78c182 (I guess?)

Right.

Cc: stable@...r.kernel.org # v4.0+
Fixes: c8d78c1823f4 ("mm: replace remap_file_pages() syscall with emulation")

-- 
 Kirill A. Shutemov