lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Wed, 30 Dec 2009 13:15:40 +0800 From: Wu Fengguang <fengguang.wu@...el.com> To: Andi Kleen <andi@...stfloor.org> Cc: Quentin Barnes <qbarnes+nfs@...oo-inc.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org>, linux-fsdevel@...r.kernel.org, Nick Piggin <npiggin@...e.de>, Steven Whitehouse <swhiteho@...hat.com> Subject: Re: [RFC][PATCH] Disabling read-ahead makes I/O of large reads small Andi, On Wed, Dec 30, 2009 at 02:04:43AM +0800, Andi Kleen wrote: > Quentin Barnes <qbarnes+nfs@...oo-inc.com> 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-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists