From: Andrea Arcangeli <aarcange@redhat.com>
To: Prakash Sangappa <prakash.sangappa@oracle.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-api@vger.kernel.org, rppt@linux.vnet.ibm.com,
akpm@linux-foundation.org, mike.kravetz@oracle.com
Subject: Re: [RESEND PATCH 1/2] userfaultfd: Add feature to request for a signal delivery
Date: Wed, 26 Jul 2017 16:19:22 +0200 [thread overview]
Message-ID: <20170726141922.GV29716@redhat.com> (raw)
In-Reply-To: <1500958062-953846-2-git-send-email-prakash.sangappa@oracle.com>
On Tue, Jul 25, 2017 at 12:47:41AM -0400, Prakash Sangappa wrote:
> In some cases, userfaultfd mechanism should just deliver a SIGBUS signal
> to the faulting process, instead of the page-fault event. Dealing with
> page-fault event using a monitor thread can be an overhead in these
> cases. For example applications like the database could use the signaling
> mechanism for robustness purpose.
>
> Database uses hugetlbfs for performance reason. Files on hugetlbfs
> filesystem are created and huge pages allocated using fallocate() API.
> Pages are deallocated/freed using fallocate() hole punching support.
> These files are mmapped and accessed by many processes as shared memory.
> The database keeps track of which offsets in the hugetlbfs file have
> pages allocated.
>
> Any access to mapped address over holes in the file, which can occur due
> to bugs in the application, is considered invalid and expect the process
> to simply receive a SIGBUS. However, currently when a hole in the file is
> accessed via the mapped address, kernel/mm attempts to automatically
> allocate a page at page fault time, resulting in implicitly filling the
> hole in the file. This may not be the desired behavior for applications
> like the database that want to explicitly manage page allocations of
> hugetlbfs files.
>
> Using userfaultfd mechanism with this support to get a signal, database
> application can prevent pages from being allocated implicitly when
> processes access mapped address over holes in the file.
>
> This patch adds UFFD_FEATURE_SIGBUS feature to userfaultfd mechnism to
> request for a SIGBUS signal.
>
> See following for previous discussion about the database requirement
> leading to this proposal as suggested by Andrea.
>
> http://www.spinics.net/lists/linux-mm/msg129224.html
>
> Signed-off-by: Prakash Sangappa <prakash.sangappa@oracle.com>
> ---
> fs/userfaultfd.c | 3 +++
> include/uapi/linux/userfaultfd.h | 10 +++++++++-
> 2 files changed, 12 insertions(+), 1 deletions(-)
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
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next prev parent reply other threads:[~2017-07-26 14:19 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-25 4:47 [RESEND PATCH 0/2] userfaultfd: Add feature to request for a signal delivery Prakash Sangappa
2017-07-25 4:47 ` [RESEND PATCH 1/2] " Prakash Sangappa
2017-07-26 7:54 ` Mike Rapoport
2017-07-26 14:19 ` Andrea Arcangeli [this message]
2017-07-27 11:58 ` Michal Hocko
2017-07-28 1:13 ` Prakash Sangappa
2017-07-25 4:47 ` [RESEND PATCH 2/2] userfaultfd: selftest: Add tests for UFFD_FREATURE_SIGBUS Prakash Sangappa
2017-07-26 7:53 ` Mike Rapoport
2017-07-26 18:54 ` Prakash Sangappa
2017-07-26 14:27 ` Andrea Arcangeli
2017-07-26 19:02 ` Prakash Sangappa
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