From: Hugh Dickins <hughd@google.com>
To: David Herrmann <dh.herrmann@gmail.com>
Cc: linux-kernel@vger.kernel.org,
Michael Kerrisk <mtk.manpages@gmail.com>,
Ryan Lortie <desrt@desrt.ca>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
linux-api@vger.kernel.org, Greg Kroah-Hartman <greg@kroah.com>,
john.stultz@linaro.org,
Lennart Poettering <lennart@poettering.net>,
Daniel Mack <zonque@gmail.com>, Kay Sievers <kay@vrfy.org>,
Hugh Dickins <hughd@google.com>,
Tony Battersby <tonyb@cybernetics.com>,
Andy Lutomirski <luto@amacapital.net>
Subject: Re: [RFC v3 6/7] shm: wait for pins to be released when sealing
Date: Wed, 16 Jul 2014 03:09:58 -0700 (PDT) [thread overview]
Message-ID: <alpine.LSU.2.11.1407160308550.1775@eggly.anvils> (raw)
In-Reply-To: <1402655819-14325-7-git-send-email-dh.herrmann@gmail.com>
On Fri, 13 Jun 2014, David Herrmann wrote:
> We currently fail setting SEAL_WRITE in case there're pending page
> references. This patch extends the pin-tests to wait up to 150ms for all
> references to be dropped. This is still not perfect in that it doesn't
> account for harmless read-only pins, but it's much better than a hard
> failure.
>
> Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Right, I didn't look through the patch itself, just compared the result
with what I sent. Okay, you prefer to separate out shmem_tag_pins().
Yes, it looks fine. There's just one change I'd like at this stage,
something I realized shortly after sending the code fragment: please
add a call to lru_add_drain() at the head of shmem_tag_pins(). The
reason being that lru_add_drain() is local to the cpu, so cheap, and
in many cases will bring down all the raised refcounts right then.
Whereas lru_add_drain_all() in the first scan of shmem_wait_for_pins()
is much more expensive, involving inter-processor interrupts to do
that on all cpus: it is appropriate to call it at that point, but we
really ought to try the cheaper lru_add_drain() at the earlier stage.
I would also like never to embark on this scan of the radix_tree
and wait for pins, if the pages were never given out in a VM_SHARED
mapping - or is that unrealistic, because every memfd is read-write,
and typical initialization expected to be by mmap() rather than write()?
But anyway, you're quite right not to get into that at this stage:
it's best left as an optimization once the basics are safely in.
Hugh
next prev parent reply other threads:[~2014-07-16 10:11 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-13 10:36 [PATCH v3 0/7] File Sealing & memfd_create() David Herrmann
2014-06-13 10:36 ` [PATCH v3 1/7] mm: allow drivers to prevent new writable mappings David Herrmann
2014-07-09 8:55 ` Hugh Dickins
2014-07-19 16:12 ` David Herrmann
2014-06-13 10:36 ` [PATCH v3 2/7] shm: add sealing API David Herrmann
2014-07-16 10:06 ` Hugh Dickins
2014-07-19 16:17 ` David Herrmann
2014-06-13 10:36 ` [PATCH v3 3/7] shm: add memfd_create() syscall David Herrmann
2014-06-13 12:27 ` Michael Kerrisk (man-pages)
2014-06-13 12:41 ` David Herrmann
2014-06-13 14:20 ` Michael Kerrisk (man-pages)
2014-06-13 16:20 ` John Stultz
2014-06-16 4:12 ` Michael Kerrisk (man-pages)
2014-07-08 18:39 ` David Herrmann
2014-06-15 10:50 ` Jann Horn
2014-07-16 10:07 ` Hugh Dickins
2014-07-19 16:29 ` David Herrmann
2014-06-13 10:36 ` [PATCH v3 4/7] selftests: add memfd_create() + sealing tests David Herrmann
2014-07-16 10:07 ` Hugh Dickins
2014-07-19 16:31 ` David Herrmann
2014-06-13 10:36 ` [PATCH v3 5/7] selftests: add memfd/sealing page-pinning tests David Herrmann
2014-07-16 10:08 ` Hugh Dickins
2014-07-19 16:32 ` David Herrmann
2014-06-13 10:36 ` [RFC v3 6/7] shm: wait for pins to be released when sealing David Herrmann
2014-07-16 10:09 ` Hugh Dickins [this message]
2014-07-19 16:36 ` David Herrmann
2014-06-13 10:36 ` [RFC v3 7/7] shm: isolate pinned pages when sealing files David Herrmann
2014-06-13 15:06 ` Andy Lutomirski
2014-06-13 15:27 ` David Herrmann
2014-06-13 17:23 ` Andy Lutomirski
2014-07-09 8:57 ` Hugh Dickins
2014-07-19 16:40 ` David Herrmann
2014-06-13 15:10 ` [PATCH v3 0/7] File Sealing & memfd_create() Andy Lutomirski
2014-06-13 15:15 ` David Herrmann
2014-06-13 15:17 ` Andy Lutomirski
2014-06-13 15:33 ` David Herrmann
2014-06-17 9:54 ` Florian Weimer
2014-06-17 10:01 ` David Herrmann
2014-06-17 10:04 ` Florian Weimer
2014-06-17 10:10 ` David Herrmann
2014-06-17 12:13 ` Florian Weimer
2014-06-17 13:26 ` David Herrmann
[not found] ` <CALCETrVpZ0vFM4usHK+tQhk234Y2jWzB1522kGcGvdQQFAqsZQ@mail.gmail.com>
2014-06-17 16:36 ` David Herrmann
2014-06-17 16:41 ` Andy Lutomirski
2014-06-17 16:51 ` David Herrmann
2014-06-17 17:01 ` Andy Lutomirski
2014-06-17 20:31 ` Hugh Dickins
2014-06-17 21:25 ` Andy Lutomirski
2014-07-08 16:54 ` David Herrmann
2014-07-09 8:53 ` Hugh Dickins
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