Invalidating dentries

Invalidating dentries

[Jan Engelhardt]

Hello list,


how can I invalidate all buffered/cached dentries so that ls -l /somefolder 
will definitely go read the harddisk?


Jan Engelhardt
-- 

Re: Invalidating dentries

[linux-os]

On Mon, 21 Mar 2005, Jan Engelhardt wrote:

> Hello list,
>
>
> how can I invalidate all buffered/cached dentries so that ls -l /somefolder
> will definitely go read the harddisk?
>

fsync() on the file(s) in the directory then fsync() on the directory
itself. For this, one can open the directory as though it was
just a file, you don't need opendir().

FYI, this is what `man fsync` promises. It may be broken. Last
time I checked, one needed to umount() the file-system to make
sure the directories were updated. The problem may be that
somebody can have either the directory or a file within it
open. Until they get out, the directory entry may not actually
be finalized. Oh,... Unix/Linux doesn't have "folders". That's
some M$ thing. Real operating systems have directories. Your
GUI may have folders, just like it may have little houses,
trash-cans, red hats, and other odd widgets. However, the
operating system doesn't.

>
> Jan Engelhardt
> --


Cheers,
Dick Johnson
Penguin : Linux version 2.6.11 on an i686 machine (5537.79 BogoMips).
  Notice : All mail here is now cached for review by Dictator Bush.
                  98.36% of all statistics are fiction.

Re: Invalidating dentries

[Robert Hancock]

linux-os wrote:
> On Mon, 21 Mar 2005, Jan Engelhardt wrote:
> 
>> Hello list,
>>
>>
>> how can I invalidate all buffered/cached dentries so that ls -l 
>> /somefolder
>> will definitely go read the harddisk?
>>
> 
> fsync() on the file(s) in the directory then fsync() on the directory
> itself. For this, one can open the directory as though it was
> just a file, you don't need opendir().

I don't think this is what they want, it sounds like they want to 
effectively clear the read cache for the file system. I'm not sure 
there's an easy way to do that other than maybe umounting and mounting 
the file system again..

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@nospamshaw.ca
Home Page: http://www.roberthancock.com/

Re: Invalidating dentries

[Andrew Morton]

Jan Engelhardt <jengelh@linux01.gwdg.de> wrote:
>
> how can I invalidate all buffered/cached dentries so that ls -l /somefolder 
>  will definitely go read the harddisk?

Patch the kernel?

There's no way of doing this apart from unmount/mount, or by forcing a ton
of memory pressure and hoping that the dentries get reclaimed.

A quick way of doing it would be to add a new mount option to the
filesystem and call shrink_dcache_sb() from there.  do `mount -o
remount,shrink_dcache'.

Re: Invalidating dentries

[Jan Engelhardt]

>> how can I invalidate all buffered/cached dentries so that ls -l /somefolder 
>>  will definitely go read the harddisk?
>
>Patch the kernel?

Great idea.

>A quick way of doing it would be to add a new mount option to the
>filesystem and call shrink_dcache_sb() from there.  do `mount -o
>remount,shrink_dcache'.

I doubt that there is a way to define an option applicable to all fs?
But thanks for the idea.


Jan Engelhardt
--