From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Morton <akpm@digeo.com>
Subject: Re: simultaneous creates in a directory
Date: Fri, 27 Sep 2002 12:44:18 -0700
Sender: linux-fsdevel-owner@vger.kernel.org
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To: Matthew Wilcox <willy@debian.org>
List-Id: linux-fsdevel.vger.kernel.org

Matthew Wilcox wrote:
> 
> At startup, tiobench does a large number of open(O_CREAT) calls, all
> in the same directory.  This leads to a large number of processes all
> trying to do down() on the parent directory's i_sem.  That wouldn't be
> so bad, but each one is sleeping with an entire page (of ZONE_NORMAL)
> allocated.  800MB of ZONE_NORMAL / 4k pages.. ok, it'd take 200,000
> tasks to completely OOM your box, but a user can certainly make life
> difficult for us with fewer tasks.
> 
> The most important question is: Do we care?  tiobench is only a benchmark.

If the fs was mounted -o sync or -o dirsync, those creates would involve
synchronous I/O inside i_sem.  So the problem is potentially more serious
in such a setup.

Even then, do we care?  Well hrm.  One page of ZONE_NORMAL per process
doesn't sound like the end of the world...