Namecache lock contention?

[John Baldwin]

On Friday, January 28, 2011 8:46:07 am Ivan Voras wrote:
> I have this situation on a PHP server:
> 
> 36623 www         1  76    0   237M 30600K *Name   6   0:14 47.27% php-cgi
> 36638 www         1  76    0   237M 30600K *Name   3   0:14 46.97% php-cgi
> 36628 www         1 105    0   237M 30600K *Name   2   0:14 46.88% php-cgi
> 36627 www         1 105    0   237M 30600K *Name   0   0:14 46.78% php-cgi
> 36639 www         1 105    0   237M 30600K *Name   5   0:14 46.58% php-cgi
> 36643 www         1 105    0   237M 30600K *Name   7   0:14 46.39% php-cgi
> 36629 www         1  76    0   237M 30600K *Name   1   0:14 46.39% php-cgi
> 36642 www         1 105    0   237M 30600K *Name   2   0:14 46.39% php-cgi
> 36626 www         1 105    0   237M 30600K *Name   5   0:14 46.19% php-cgi
> 36654 www         1 105    0   237M 30600K *Name   7   0:13 46.19% php-cgi
> 36645 www         1 105    0   237M 30600K *Name   1   0:14 45.75% php-cgi
> 36625 www         1 105    0   237M 30600K *Name   0   0:14 45.56% php-cgi
> 36624 www         1 105    0   237M 30600K *Name   6   0:14 45.56% php-cgi
> 36630 www         1  76    0   237M 30600K *Name   7   0:14 45.17% php-cgi
> 36631 www         1 105    0   237M 30600K RUN     4   0:14 45.17% php-cgi
> 36636 www         1 105    0   237M 30600K *Name   3   0:14 44.87% php-cgi
> 
> It looks like periodically most or all of the php-cgi processes are 
> blocked in "*Name" for long enough that "top" notices, then continue, 
> probably in a "thundering herd" way. From grepping inside /sys the most 
> likely suspect seems to be something in the namecache, but I can't find 
> exactly a symbol named "Name" or string beginning with "Name" that would 
> be connected to a lock.

In vfs_cache.c:

static struct rwlock cache_lock;
RW_SYSINIT(vfscache, &cache_lock, "Name Cache");

What are the php scripts doing?  Do they all try to create and delete files at 
the same time (or do renames)?

-- 
John Baldwin