From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Ming Lin <mlin@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Hugh Dickins <hughd@google.com>, Simon Ser <contact@emersion.fr>,
Matthew Wilcox <willy@infradead.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org
Subject: Re: [PATCH v2 2/2] mm: adds NOSIGBUS extension to mmap()
Date: Fri, 4 Jun 2021 18:24:07 +0300 [thread overview]
Message-ID: <20210604152407.ouchyfuxjvchfroe@box> (raw)
In-Reply-To: <1622792602-40459-3-git-send-email-mlin@kernel.org>
On Fri, Jun 04, 2021 at 12:43:22AM -0700, Ming Lin wrote:
> Adds new flag MAP_NOSIGBUS of mmap() to specify the behavior of
> "don't SIGBUS on fault". Right now, this flag is only allowed
> for private mapping.
That's not what your use case asks for.
SIGBUS can be generated for a number of reasons, not only on fault beyond
end-of-file. vmf_error() would convert any errno, except ENOMEM to
VM_FAULT_SIGBUS.
Do you want to ignore -EIO or -ENOSPC? I don't think so.
> For MAP_NOSIGBUS mapping, map in the zero page on read fault
> or fill a freshly allocated page with zeroes on write fault.
I don't like the resulting semantics: if you had a read fault beyond EOF
and got zero page, you will still see zero page even if the file grows.
Yes, it's allowed by POSIX for MAP_PRIVATE to get out-of-sync with the
file, but it's not what users used to.
It might be enough for the use case, but I would rather avoid one-user
features.
--
Kirill A. Shutemov
next prev parent reply other threads:[~2021-06-04 15:55 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-04 7:43 [PATCH v2 0/2] mm: support NOSIGBUS on fault of mmap Ming Lin
2021-06-04 7:43 ` [PATCH v2 1/2] mm: make "vm_flags" be an u64 Ming Lin
2021-06-04 7:43 ` [PATCH v2 2/2] mm: adds NOSIGBUS extension to mmap() Ming Lin
2021-06-04 15:24 ` Kirill A. Shutemov [this message]
2021-06-04 16:22 ` Ming Lin
2021-06-28 14:27 ` Vivek Goyal
2021-06-30 16:37 ` Ming Lin
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