linux-kernel - Re: [PATCHv2 0/2] remap_file

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Date:	Mon, 12 May 2014 09:16:38 +0400
From:	Konstantin Khlebnikov <koct9i@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Armin Rigo <arigo@...es.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>, peterz@...radead.org,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCHv2 0/2] remap_file_pages() decommission

On Mon, May 12, 2014 at 7:36 AM, Andi Kleen <andi@...stfloor.org> wrote:
> Armin Rigo <arigo@...es.org> writes:
>
>> Here is a note from the PyPy project (mentioned earlier in this
>> thread, and at https://lwn.net/Articles/587923/ ).
>
> Your use is completely bogus. remap_file_pages() pins everything
> and disables any swapping for the area.

Wait, what's wrong with swapping pages from non-linear vmas?
try_to_umap() can handle them, though not very effectively.

Some time ago I was thinking about tracking rmap for non-linear vmas, something
like second-level tree of sub-vmas stored in non-linear vma. This
could be done using
exising vm_area_struct, and in rmap tree everything will looks just as normal.
We'll waste some kernel memory, but it also will remove complexity from rmap and
make non-linear vmas usable for all filesystems not just for shmem.

But it's not worth. I ACK killing it.

Maybe we should keep flag on vma and hide/merge them in proc/maps.
Bloating files/dirs in proc might be bigger problem than non-existent
performance regression.

>
> -Andi
> --
> ak@...ux.intel.com -- Speaking for myself only
>
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