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SubjectRe: drop_caches ...
On Wed, Mar 04, 2009 at 12:32:02PM +0200, Markus wrote:
> Hello Fengguang!
>
> > Hi Markus,
> >
> > On Wed, Mar 04, 2009 at 10:57:33AM +0100, Markus wrote:
> > > Hello!
> > >
> > > I have a small problem. Maybe its just a misunderstanding but I cant
> > > solve it.
> > >
> > > I think that writing "3" to drop_caches should drop all buffers and
> > > caches which are already written. So its recommended to put a "sync"
> > > infront of it.
> > > So I did "free -m ; sync ; echo 3 > /proc/sys/vm/drop_caches ;
> free -m"
> > > And it gave me:
> > > total used free shared buffers
> > > cached
> > > Mem: 3950 3922 28 0 1
> > > 879
> > > -/+ buffers/cache: 3041 909
> > > Swap: 5342 205 5136
> > > total used free shared buffers
> > > cached
> > > Mem: 3950 3907 43 0 0
> > > 864
> > > -/+ buffers/cache: 3041 908
> > > Swap: 5341 206 5135
> > >
> > > So the buffer was 1 and is 0 afterthat. But cached is at 879 MB
> before
> > > and is still 864 MB (!!!) after that!
> > >
> > > I am at swappiness=0 and when I remove and readd one swap-partition
> > > after another (so there is always swap). It will keep the cached and
> > > put the swapped memory on other swaps?!
> > >
> > > I _think_ thats not the way it should go?
> > >
> > > It would be really kind if someone could explain that issue and
> > > what "cached" is at all!
> >
> > 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?

Thanks,
Fengguang



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