svn commit: r292299 - head/sys/kern

[Konstantin Belousov]

On Wed, Dec 16, 2015 at 12:13:16AM +0000, Adrian Chadd wrote:
> Author: adrian
> Date: Wed Dec 16 00:13:16 2015
> New Revision: 292299
> URL: https://svnweb.freebsd.org/changeset/base/292299
> 
> Log:
>   Don't call wakeup if we're just returning reserved space; just
>   return the reservation and wait for more space to appear.
Issue which is supposedly fixed by the commit is not due to the possibly
excessive wakeups. bufspace_release() and bufspace_wakeup() clear
the needsbuffer variable, while the code flow in getnewbuf() calls
bufspace_wait() to wait for the condition, which prevented the buffer
allocation from succeeding, to pass.

>   
>   Submitted by:	jeff
>   Reviewed by:	kib
> 
> Modified:
>   head/sys/kern/vfs_bio.c
> 
> Modified: head/sys/kern/vfs_bio.c
> ==============================================================================
> --- head/sys/kern/vfs_bio.c	Wed Dec 16 00:09:57 2015	(r292298)
> +++ head/sys/kern/vfs_bio.c	Wed Dec 16 00:13:16 2015	(r292299)
> @@ -2909,7 +2909,7 @@ getnewbuf(struct vnode *vp, int slpflag,
>  	} while(buf_scan(false) == 0);
>  
>  	if (reserved)
> -		bufspace_release(maxsize);
> +		atomic_subtract_long(&bufspace, maxsize);
>  	if (bp != NULL) {
>  		bp->b_flags |= B_INVAL;
>  		brelse(bp);