svn commit: r291460 - head/sys/kern

[Kubilay Kocak]

On 30/11/2015 8:42 AM, Kirk McKusick wrote:
> Author: mckusick
> Date: Sun Nov 29 21:42:26 2015
> New Revision: 291460
> URL: https://svnweb.freebsd.org/changeset/base/291460
> 
> Log:
>   As the kernel allocates and frees vnodes, it fully initializes them
>   on every allocation and fully releases them on every free.  These
>   are not trivial costs: it starts by zeroing a large structure then
>   initializes a mutex, a lock manager lock, an rw lock, four lists,
>   and six pointers. And looking at vfs.vnodes_created, these operations
>   are being done millions of times an hour on a busy machine.
>   
>   As a performance optimization, this code update uses the uma_init
>   and uma_fini routines to do these initializations and cleanups only
>   as the vnodes enter and leave the vnode_zone. With this change the
>   initializations are only done kern.maxvnodes times at system startup
>   and then only rarely again. The frees are done only if the vnode_zone
>   shrinks which never happens in practice. For those curious about the
>   avoided work, look at the vnode_init() and vnode_fini() functions in
>   kern/vfs_subr.c to see the code that has been removed from the main
>   vnode allocation/free path.
>   
>   Reviewed by: kib
>   Tested by:   Peter Holm
> 
> Modified:
>   head/sys/kern/vfs_subr.c
> 

Kirk,

Very interesting.

Any estimation / expectation on the performance impact^W benefit of
this, and in what scenario's / use-cases it might be particularly
beneficial? Any benchmarks or tests you can share?

./koobs