[Pvfs2-users] running executables from PVFS filesystems

[Murali Vilayannur]

Hi,
Problem with running executables off PVFS volumes is that page-ins of the
text segment will cause a flurry of I/O requests of 4KB/8KB (as the page
size may be) to the servers which is really not optimal and could hence
slow things down for a lot of people.
In PVFS2, we have a readahead mmap cache in the client core daemon which
can be enabled by configure --enable-mmap-racache which will basically
help in such situations by prefetching the entire executable and service
it from client-core cache instead of from servers.
Perhaps that can mitigate this problem a bit..
Hope this helps,
Murali

On Tue, 8 Aug 2006, Mark Bartelt wrote:

> Someone forwarded me the following URL ...
>
> http://thunderhead.gsfc.nasa.gov/Users_Guide/PVFS.shtml
>
> ... an excerpt from which is appended below.  Does this
> seem reasonable?  I'm a bit puzzled about why running an
> executable that happens to live on a PVFS filesystem is
> likely to cause much grief.  Is it frequent page-ins of
> the a.out's text segment, or something else entirely?
>
> (Or for that matter, is the claim below even true?)
>
> =============================================
>
>  Can I run my executables from my user directory in
>  /data1 (on the PVFS server)?
>
>  NO, PLEASE DON'T DO THIS!  It will cause PVFS to run
>  painfully slowly for all of the users and the sysadmins
>  will become quite manic.  Be a good neighbor, and run
>  from home/rhome, please don't run executables from PVFS.
>
>  If you decide to run from PVFS anyway, you could correctly
>  visualize your office as being similar to Frankenstein's
>  castle being stormed by furious torch-bearing Thunderhead
>  users and anxious system administrators.
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