From: Zan Lynx <zlynx@acm.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
linux-kernel@vger.kernel.org, Hugh Dickins <hughd@google.com>
Subject: Re: [PATCH 1/2] msync: support syncing a small part of the file
Date: Wed, 13 Jun 2012 15:51:33 -0600 [thread overview]
Message-ID: <1339624293.2080.24.camel@knife> (raw)
In-Reply-To: <20120613142614.6af42ef5.akpm@linux-foundation.org>
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On Wed, 2012-06-13 at 14:26 -0700, Andrew Morton wrote:
> On Thu, 31 May 2012 22:43:54 +0200
> Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> > msync does not need to flush changes to the entire file, even with MS_SYNC.
> > Instead, it can use vfs_fsync_range to only synchronize a part of the file.
> >
> > In addition, not all metadata has to be synced; msync is closer to
> > fdatasync than it is to msync. So, pass 1 to vfs_fsync_range.
>
> Would be nice, but if applications were previously assuming that an
> msync() was syncing the whole file, this patch will secretly and subtly
> break them. Convince me that this change won't weaken anyone's data
> integrity ;)
As an interested observer and a programmer who uses msync()...
I never assumed msync() did the whole file. It has an address and length
argument. I always assumed it only looked for dirty pages within that
range. That is also what the msync() documentation claims.
As for weakening data integrity because of assumptions programmers *may*
have made, I think this is a bad argument which followed to its logical
conclusion can only lead to requiring an implicit sync() before and
after every system call. :-)
Asking programmers to use sync_file_range() is not a replacement for
improving msync() because msync() is POSIX and can be used everywhere.
sync_file_range() requires Linux specific code.
--
Knowledge Is Power
Power Corrupts
Study Hard
Be Evil
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next prev parent reply other threads:[~2012-06-13 22:15 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-31 20:43 [PATCH 0/2] msync improvements Paolo Bonzini
2012-05-31 20:43 ` [PATCH 1/2] msync: support syncing a small part of the file Paolo Bonzini
2012-06-13 21:26 ` Andrew Morton
2012-06-13 21:51 ` Zan Lynx [this message]
2012-06-13 22:08 ` Andrew Morton
2012-06-14 8:57 ` Paolo Bonzini
2012-05-31 20:43 ` [PATCH 2/2] msync: start async writeout when MS_ASYNC Paolo Bonzini
2012-06-13 21:29 ` Andrew Morton
2012-06-14 9:02 ` Paolo Bonzini
2012-06-14 10:07 ` Andrew Morton
2012-06-14 10:19 ` Paolo Bonzini
2012-06-14 12:24 ` Paolo Bonzini
2012-06-12 15:38 ` [PATCH 0/2] msync improvements Paolo Bonzini
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