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Date: Tue, 30 Jun 2015 08:54:41 +0300
From: Konstantin Belousov <kostikbel@gmail.com>
To: Julian Elischer <julian@freebsd.org>
Cc: Ed Schouten <ed@nuxi.nl>, src-committers@freebsd.org,
 svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject: Re: svn commit: r284887 - in head/sys: kern sys ufs/ffs
Message-ID: <20150630055441.GY2080@kib.kiev.ua>
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On Tue, Jun 30, 2015 at 11:19:30AM +0800, Julian Elischer wrote:
> On 6/29/15 8:19 PM, Ed Schouten wrote:
> > Hi Kostik,
> >
> > 2015-06-27 11:44 GMT+02:00 Konstantin Belousov <kib@freebsd.org>:
> >> @@ -2056,6 +2072,8 @@ ffs_bufwrite(struct buf *bp)
> >>                  if (bp->b_vflags & BV_BKGRDINPROG)
> >>                          panic("bufwrite: still writing");
> >>          }
> >> +       if ((bp->b_vflags & BV_BKGRDERR) != 0)
> >> +               bp->b_vflags &= ~BV_BKGRDERR;
> >>          BO_UNLOCK(bp->b_bufobj);
> >>
> >>          /*
> > This if-statement could be removed, right? The bit could just be
> > cleared unconditionally.
> true but it replaces a read and write with just a read in the case of 
> no change.

Th cache line is dirty already, test before the rwm operation would not
give any optimizations.