Andi, On Wed, Dec 30, 2009 at 02:04:43AM +0800, Andi Kleen wrote: > Quentin Barnes <qbarnes+nfs@xxxxxxxxxxxxx> writes: > > cc fengguang who is Mr.Readahead. The full description+patch > is in the archives. Thank you for the CC. > > In porting some application code to Linux, its performance over > > NFSv3 on Linux is terrible. I'm posting this note to LKML since > > the problem was actually tracked back to the VFS layer. > [...] > > I have no idea if my patch is the appropriate fix. I'm well out of > > my area in this part of the kernel. It solves this one problem, but > > I have no idea how many boundary cases it doesn't cover or even if > > it is the right way to go about addressing this issue. > > > > Is this behavior of shorting I/O of read(2) considered a bug? And > > is this approach for a fix approriate? > > It sounds like a (performance) bug to me. Yes it's a bug. It hit my mind in some early days.. I should be blamed to lose track of it. > >From a quick look your fix looks reasonable to me. Yes, it's reasonable to directly call force_page_cache_readahead() in this case. However the ra_pages=0 trick in fadvise also asks for fix. We'd better let it set a readahead flag, because ra_pages=0 is used in many other places to really disable the (heuristic|force) readahead. See the second patch's description for more details. Thanks, Fengguang -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
