Re: drop_caches ...

Wu Fengguang
2009-03-04T11:58:01Z

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