direct i/o problem with 2.4.20 and 2.4.21rc7

direct i/o problem with 2.4.20 and 2.4.21rc7

[Larry Auton]

I have an application that requires direct i/o to thousands of files.
On 2.4.19 the open's would eventually fail (at around 7200 files).
On 2.4.20 and 2.4.21rc7 the machine hangs.

Here's a sample program to do the deed:

    wget http://www.skarven.net/lda/crashme.c
    cc -o crashme crashme.c	# compile it
    ./crashme 4000		# OK
    ./crashme 9999		# CRASH

It's a little obfuscated to eliminate the need for root privileges to
mess with rlimit. It simply opens a bunch of files with O_DIRECT and,
when enough files are open, the system will hang.

The system hangs when '/proc/slabinfo' reports that 'kiobuf' reaches 
just over 7230 active objects. I don't believe that this problem is
specific to any particular file system as the failure occurs when
using both ext2 and reiserfs.

Larry Auton