Re: drop_caches ...

[Zdenek Kabelac <zkabelac@redhat.com>]

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