Re: [PATCH]vmscan: handle underflow for get_scan_ratio

[Shaohua Li]

On Tue, 2010-03-30 at 14:08 +0800, KOSAKI Motohiro wrote:
> Hi
> 
> > Commit 84b18490d1f1bc7ed5095c929f78bc002eb70f26 introduces a regression.
> > With it, our tmpfs test always oom. The test has a lot of rotated anon
> > pages and cause percent[0] zero. Actually the percent[0] is a very small
> > value, but our calculation round it to zero. The commit makes vmscan
> > completely skip anon pages and cause oops.
> > An option is if percent[x] is zero in get_scan_ratio(), forces it
> > to 1. See below patch.
> > But the offending commit still changes behavior. Without the commit, we scan
> > all pages if priority is zero, below patch doesn't fix this. Don't know if
> > It's required to fix this too.
> 
> Can you please post your /proc/meminfo 
attached.
> and reproduce program? I'll digg it.
our test is quite sample. mount tmpfs with double memory size and store several
copies (memory size * 2/G) of kernel in tmpfs, and then do kernel build.
for example, there is 3G memory and then tmpfs size is 6G and there is 6
kernel copy.
> Very unfortunately, this patch isn't acceptable. In past time, vmscan 
> had similar logic, but 1% swap-out made lots bug reports. 
can you elaborate this?
Completely restore previous behavior (do full scan with priority 0) is
ok too.
MemTotal:        3078372 kB
MemFree:           34612 kB
Buffers:             960 kB
Cached:          2577644 kB
SwapCached:        24580 kB
Active:          2125712 kB
Inactive:         541972 kB
Active(anon):    2120276 kB
Inactive(anon):   534696 kB
Active(file):       5436 kB
Inactive(file):     7276 kB
Unevictable:           0 kB
Mlocked:               0 kB
SwapTotal:       6297472 kB
SwapFree:        6184988 kB
Dirty:              1720 kB
Writeback:         24024 kB
AnonPages:         64888 kB
Mapped:             3996 kB
Shmem:           2566004 kB
Slab:             290416 kB
SReclaimable:     113840 kB
SUnreclaim:       176576 kB
KernelStack:        3072 kB
PageTables:         6832 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:     7836656 kB
Committed_AS:    2811564 kB
VmallocTotal:   34359738367 kB
VmallocUsed:      289724 kB
VmallocChunk:   34359444080 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
DirectMap4k:       10240 kB
DirectMap2M:     3127296 kB