linux-kernel - Re: Convert namespace

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Message-ID: <20070517071720.GC4462@in.ibm.com>
Date:	Thu, 17 May 2007 12:47:20 +0530
From:	Bharata B Rao <bharata@...ux.vnet.ibm.com>
To:	Al Viro <viro@....linux.org.uk>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Convert namespace_sem to a mutex

On Thu, May 17, 2007 at 06:00:46AM +0100, Al Viro wrote:
> On Thu, May 17, 2007 at 10:20:41AM +0530, Bharata B Rao wrote:
> > From: Bharata B Rao <bharata@...ux.vnet.ibm.com>
> > 
> > namespace_sem is a rwsem. It is acquired as read sem at only one place(used
> > by /proc/mounts, /proc/<pid>/mounts and /proc/<pid>/mountstats). In all other
> > cases it is acquired as a write sem. So, as there is not more than one reader
> > for this sem, this can be a generic sem (and not rwsem) and if so it can be
> > a mutex.
> 
> Except that read accesses outnumber write ones by far and we have no reason
> for serializing them against each other.  NAK.

Ok, I wasn't aware that this rwsem had many concurrent readers. From whatever
little I could see (during system boot and during kernel compilation with
make -j), the number of concurrent readers very rarely touched 3 and was 1
mostly. May be there are other concurrent readers of this sem. Any idea
from where they could be coming from ?

Regards,
Bharata.
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