Re: drop_caches ...

[Wu Fengguang]

On Wed, Mar 04, 2009 at 01:29:40PM +0200, Markus wrote:
> > > > The memory mapped pages won't be dropped in this way.
> > > > "cat /proc/meminfo" will show you the number of mapped pages.
> > > 
> > > # sync ; echo 3 > /proc/sys/vm/drop_caches ; free -m ; 
> cat /proc/meminfo
> > >              total       used       free     shared    buffers     
> > > cached
> > > Mem:          3950       3262        688          0          0        
> > > 359
> > > -/+ buffers/cache:       2902       1047
> > > Swap:         5890       1509       4381
> > > MemTotal:        4045500 kB
> > > MemFree:          705180 kB
> > > Buffers:             508 kB
> > > Cached:           367748 kB
> > > SwapCached:       880744 kB
> > > Active:          1555032 kB
> > > Inactive:        1634868 kB
> > > Active(anon):    1527100 kB
> > > Inactive(anon):  1607328 kB
> > > Active(file):      27932 kB
> > > Inactive(file):    27540 kB
> > > Unevictable:         816 kB
> > > Mlocked:               0 kB
> > > SwapTotal:       6032344 kB
> > > SwapFree:        4486496 kB
> > > Dirty:                 0 kB
> > > Writeback:             0 kB
> > > AnonPages:       2378112 kB
> > > Mapped:            52196 kB
> > > Slab:              65640 kB
> > > SReclaimable:      46192 kB
> > > SUnreclaim:        19448 kB
> > > PageTables:        28200 kB
> > > NFS_Unstable:          0 kB
> > > Bounce:                0 kB
> > > WritebackTmp:          0 kB
> > > CommitLimit:     8055092 kB
> > > Committed_AS:    4915636 kB
> > > VmallocTotal:   34359738367 kB
> > > VmallocUsed:       44580 kB
> > > VmallocChunk:   34359677239 kB
> > > DirectMap4k:     3182528 kB
> > > DirectMap2M:     1011712 kB
> > > 
> > > The cached reduced to 359 MB (after the dropping).
> > > I dont know where to read the "number of mapped pages".
> > > "Mapped" is about 51 MB.
> > 
> > Does your tmpfs store lots of files?
> 
> Dont think so:
> 
> # df -h
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/md6               14G  8.2G  5.6G  60% /
> udev                   10M  304K  9.8M   3% /dev
> cachedir              4.0M  100K  4.0M   3% /lib64/splash/cache
> /dev/md4               19G   15G  3.1G  83% /home
> /dev/md3              8.3G  4.5G  3.9G  55% /usr/portage
> shm                   2.0G     0  2.0G   0% /dev/shm
> /dev/md1               99M   19M   76M  20% /boot
> 
> # mount
> /dev/md6 on / type ext3 (rw,noatime,nodiratime,barrier=0)
> /proc on /proc type proc (rw,noexec,nosuid,noatime,nodiratime)
> sysfs on /sys type sysfs (rw,nosuid,nodev,noexec)
> udev on /dev type tmpfs (rw,nosuid,size=10240k,mode=755)
> devpts on /dev/pts type devpts (rw,nosuid,noexec,gid=5,mode=620)
> cachedir on /lib64/splash/cache type tmpfs (rw,size=4096k,mode=644)
> /dev/md4 on /home type ext3 (rw,noatime,nodiratime,barrier=0)
> /dev/md3 on /usr/portage type ext4 (rw,noatime,nodiratime,barrier=0)
> shm on /dev/shm type tmpfs (rw,noexec,nosuid,nodev)
> usbfs on /proc/bus/usb type usbfs 
> (rw,noexec,nosuid,devmode=0664,devgid=85)
> automount(pid6507) on /mnt/.autofs/misc type autofs 
> (rw,fd=4,pgrp=6507,minproto=2,maxproto=4)
> automount(pid6521) on /mnt/.autofs/usb type autofs 
> (rw,fd=4,pgrp=6521,minproto=2,maxproto=4)
> /dev/md1 on /boot type ext2 (rw,noatime,nodiratime)
> 
> I dont know what exactly all that memory is used for. It varies from 
> about 300 MB to up to one GB.
> Tell me where to look and I will!

So you don't have lots of mapped pages(Mapped=51M) or tmpfs files.  It's
strange to me that there are so many undroppable cached pages(Cached=359M),
and most of them lie out of the LRU queue(Active+Inactive file=53M)...

Anyone have better clues on these 'hidden' pages?

Thanks,
Fengguang
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