From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: Armin Rigo <arigo@tunes.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
peterz@infradead.org, mingo@kernel.org
Subject: Re: [PATCHv2 0/2] remap_file_pages() decommission
Date: Thu, 8 May 2014 19:02:05 +0300 (EEST) [thread overview]
Message-ID: <20140508160205.A0EC7E009B@blue.fi.intel.com> (raw)
In-Reply-To: <CAMSv6X0+3-uNeiyEPD3sA5dA6Af_M+BT0aeVpa3qMv1aga0q9g@mail.gmail.com>
Armin Rigo wrote:
> Hi everybody,
>
> Here is a note from the PyPy project (mentioned earlier in this
> thread, and at https://lwn.net/Articles/587923/ ).
>
> Yes, we use remap_file_pages() heavily on the x86-64 architecture.
> However, the individual calls to remap_file_pages() are not
> performance-critical, so it is easy to switch to using multiple
> mmap()s. We need to perform more measurements to know exactly what
> the overhead would be, in terms notably of kernel memory.
>
> However, an issue with that approach is the upper bound on the number
> of VMAs. By default, it is not large enough. Right now, it is
> possible to remap say 10% of the individual pages from an anonymous
> mmap of multiple GBs in size; but doing so with individual calls to
> mmap hits this arbitrary limit.
The limit is not totaly random. We use ELF format for coredumps and ELF has
limitation (16-bit field) on number of sections it can store.
With ELF extended numbering we can bypass 16-bit limit, but some userspace
can be surprised by that.
> I have no particular weight to give
> for or against keeping remap_file_pages() in the kernel, but if it is
> removed or emulated, it would be a plus if the programs would run on a
> machine with the default configuration --- i.e. if you remove or
> emulate remap_file_pages(), please increase the default limit as well.
It's fine to me. Andrew?
--
Kirill A. Shutemov
next prev parent reply other threads:[~2014-05-08 16:02 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-08 12:41 [PATCHv2 0/2] remap_file_pages() decommission Kirill A. Shutemov
2014-05-08 12:41 ` [PATCH 1/2] mm: mark remap_file_pages() syscall as deprecated Kirill A. Shutemov
2014-06-12 5:48 ` Michael Kerrisk
2014-06-12 9:40 ` Kirill A. Shutemov
2014-06-12 9:44 ` Michael Kerrisk (man-pages)
2014-05-08 12:41 ` [PATCH 2/2] mm: replace remap_file_pages() syscall with emulation Kirill A. Shutemov
2014-05-08 21:57 ` Andrew Morton
2014-05-12 15:11 ` Sasha Levin
2014-05-12 17:05 ` Kirill A. Shutemov
2014-05-14 20:52 ` Sasha Levin
2014-05-14 21:17 ` Kirill A. Shutemov
2014-05-14 21:40 ` Andrew Morton
2014-05-13 7:32 ` Armin Rigo
2014-05-13 12:57 ` Sasha Levin
2014-05-08 15:35 ` [PATCHv2 0/2] remap_file_pages() decommission Linus Torvalds
2014-05-08 15:44 ` Armin Rigo
2014-05-08 16:02 ` Kirill A. Shutemov [this message]
2014-05-08 16:08 ` Linus Torvalds
2014-05-09 14:05 ` Kirill A. Shutemov
2014-05-09 15:14 ` Linus Torvalds
2014-05-09 18:19 ` Kirill A. Shutemov
2014-05-12 12:43 ` Kirill A. Shutemov
2014-05-12 14:59 ` Konstantin Khlebnikov
2014-05-12 3:36 ` Andi Kleen
2014-05-12 5:16 ` Konstantin Khlebnikov
2014-05-12 7:50 ` Armin Rigo
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