Re: drop_caches ...

Zdenek Kabelac
2009-03-04T12:32:43Z

Wu Fengguang napsal(a):
> 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?

Maybe try this:

cat /proc/`pidof X`/smaps | grep drm | wc -l

you will see some growing numbers.

Also check cat /proc/dri/0/gem_objects
there should be some number # object bytes - which should be close to your
missing cached pages.

If you are using Intel GEM driver - there is some unlimited caching issue

see: http://bugs.freedesktop.org/show_bug.cgi?id=20404

Zdenek