Re: simultaneous creates in a directory

[William Lee Irwin III <wli@holomorphy.com>]

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.

On Fri, Sep 27, 2002 at 12:44:18PM -0700, Andrew Morton wrote:
> 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...

Well, it's one of the larger contributors to one of my OOM scenarios,
which is why I asked willy to do it. Also consider /tmp/ ...


Cheers,
Bill