After upgrade from 2.4.0-test7 to 2.4.0 while running tiotest v0.3.1 I found two
following problems. 

1. Tiotest is compiled for mmap() usage and there is no swap on the system with
~200Mb free memory. Tiotest tries to create mmap'ed file with size
~memory_size*2 and soon after start gets killed by OOM killer. If I add swap
space, the kernel uses only a few Mb from it.

AFAIU, it is because out_of_memory() in oom_kill.c checks for amount swap space
left, which is always 0 without swap. Apparently, it is not correct for
"no-swap" systems.

2. Second problem is related to mmap() performance. 

I ran "./tiobench.pl --size 1024 --threads 2", which is translated to 
"./tiotest -t 2 -f 512 -r 2000 -b 4096 -d . -T", with tiotest compiled for
mmap() and for conventional read()/write() usage on 2.4.0-test7 and 2.4.0. These
are results:

Size is MB, BlkSz is Bytes, Read, Write, and Seeks are MB/sec

2.4.0-test7 with mmap() 

File   Block  Num  Seq Read    Rand Read   Seq Write  Rand Write
Dir    Size   Size   Thr Rate (CPU%) Rate (CPU%) Rate (CPU%) Rate (CPU%)
------- ------ ------- --- ----------- ----------- ----------- -----------
   .     1024   4096    2  22.44 14.7% 0.456 0.78% 10.66 22.5% 0.733 1.87%

2.4.0 with mmap() 

File   Block  Num  Seq Read    Rand Read   Seq Write  Rand Write
Dir    Size   Size   Thr Rate (CPU%) Rate (CPU%) Rate (CPU%) Rate (CPU%)
------- ------ ------- --- ----------- ----------- ----------- -----------
   .     1024   4096    2  12.53 9.02% 0.489 1.16% 10.82 15.3% 0.640 1.14%

2.4.0-test7 without mmap() 

File   Block  Num  Seq Read    Rand Read   Seq Write  Rand Write
Dir    Size   Size   Thr Rate (CPU%) Rate (CPU%) Rate (CPU%) Rate (CPU%)
------- ------ ------- --- ----------- ----------- ----------- -----------
   .     1024   4096    2  14.20 17.6% 0.502 1.28% 12.85 15.1% 0.643 1.31%

2.4.0 without mmap() 

File   Block  Num  Seq Read    Rand Read   Seq Write  Rand Write
Dir    Size   Size   Thr Rate (CPU%) Rate (CPU%) Rate (CPU%) Rate (CPU%)
------- ------ ------- --- ----------- ----------- ----------- -----------
   .     1024   4096    2  28.41 42.1% 0.541 1.35% 13.16 16.8% 0.645 1.52%

You can see, mmap() read performance dropped significantly as well as read() one
raised. Plus, "interactivity" of 2.4.0 system was much worse during mmap'ed
test, than using read() (everything was quite smooth here). 2.4.0-test7 was
badly interactive in both cases.

I use /dev/hdc on IDE channel 2 for tests and /dev/hda IDE channel 2 for swap.
hdparam output for both drives:

 multcount    =  0 (off)
 I/O support  =  0 (default 16-bit)
 unmaskirq    =  0 (off)
 using_dma    =  1 (on)
 keepsettings =  0 (off)
 nowerr       =  0 (off)
 readonly     =  0 (off)
 readahead    =  8 (on)

2.4.0 and 2.4.0-test7 were compiled with one .config via "make oldconfig".
.config 
and dmesg you can find in the attachment.

Any comments?

Regards,
Vlad