kern/178997: Heavy disk I/O may hang system

[Klaus Weber]

The following reply was made to PR kern/178997; it has been noted by GNATS.

From: Klaus Weber <fbsd-bugs-2013-1 at unix-admin.de>
To: Klaus Weber <fbsd-bugs-2013-1 at unix-admin.de>
Cc: Bruce Evans <brde at optusnet.com.au>, freebsd-gnats-submit at FreeBSD.org
Subject: Re: kern/178997: Heavy disk I/O may hang system
Date: Sun, 21 Jul 2013 19:45:25 +0200

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 On Sun, Jul 21, 2013 at 07:42:15PM +0200, Klaus Weber wrote:
 > With the following patch (also attached)
 
 Attachment was missing.
 
 Klaus
 
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 Content-Disposition: attachment; filename="bo_dirty.bv_cnt_FIX_prod.patch"
 
 Index: sys/kern/vfs_bio.c
 ===================================================================
 --- sys/kern/vfs_bio.c	(revision 253339)
 +++ sys/kern/vfs_bio.c	(working copy)
 @@ -1146,7 +1146,7 @@
  	if (bo->bo_dirty.bv_cnt > dirtybufthresh + 10) {
  		(void) VOP_FSYNC(bp->b_vp, MNT_NOWAIT, curthread);
  		altbufferflushes++;
 -	} else if (bo->bo_dirty.bv_cnt > dirtybufthresh) {
 +	} else if ( bdflush_required(bo) ) {
  		BO_LOCK(bo);
  		/*
  		 * Try to find a buffer to flush.
 @@ -1438,6 +1438,28 @@
  }
  
  /*
 + * Flushing is deemed necessary if at least one of the following is true:
 + * - bo is hogging more than dirtybufthresh buffers (previous behavior)
 + * - numdirtybuffers exceeds dirtybufthresh
 + * - we are or act as bufdaemon (TDP_NORUNNINGBUF)
 + *
 + * Used by bufbdflush (above) and ffs_bdflush (in ffs_snapshot).
 + */
 +int
 +bdflush_required(struct bufobj *bo)
 +{
 +  struct thread *td = curthread;
 +
 +  KASSERT(bo != NULL, ("bdflush_required: NULL bo"));
 +
 +  if ((bo->bo_dirty.bv_cnt > dirtybufthresh) ||
 +      (numdirtybuffers > dirtybufthresh) ||
 +      (td && (td->td_pflags & TDP_NORUNNINGBUF)) )
 +    return(1);
 +  return(0);
 +  }
 +
 +/*
   *	brelse:
   *
   *	Release a busy buffer and, if requested, free its resources.  The
 Index: sys/sys/bio.h
 ===================================================================
 --- sys/sys/bio.h	(revision 253339)
 +++ sys/sys/bio.h	(working copy)
 @@ -151,6 +151,10 @@
  #define physread physio
  #define physwrite physio
  
 +extern struct bufobj *bo;
 +int bdflush_required(struct bufobj *bo);
 +
 +
  #endif /* _KERNEL */
  
  #endif /* !_SYS_BIO_H_ */
 Index: sys/ufs/ffs/ffs_snapshot.c
 ===================================================================
 --- sys/ufs/ffs/ffs_snapshot.c	(revision 253339)
 +++ sys/ufs/ffs/ffs_snapshot.c	(working copy)
 @@ -2161,7 +2161,7 @@
  	struct buf *nbp;
  	int bp_bdskip;
  
 -	if (bo->bo_dirty.bv_cnt <= dirtybufthresh)
 +	if ( !bdflush_required(bo) )
  		return;
  
  	td = curthread;
 
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