From: Jeff Garzik Subject: Re: [PATCH 0/3] Ext3 latency improvement patches Date: Fri, 27 Mar 2009 20:14:04 -0400 Message-ID: <49CD6BCC.6080602@garzik.org> References: <1238185471-31152-1-git-send-email-tytso@mit.edu> <1238187031.27455.212.camel@think.oraclecorp.com> <1238187818.27455.217.camel@think.oraclecorp.com> <20090327213052.GC5176@mit.edu> <20090327215454.GH31071@duck.suse.cz> <20090327230902.GG5176@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit To: Theodore Tso , Jan Kara , Chris Mason , Ric Wheeler , Linux Kernel Developers List Received: from srv5.dvmed.net ([207.36.208.214]:55017 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751993AbZC1AOa (ORCPT ); Fri, 27 Mar 2009 20:14:30 -0400 In-Reply-To: <20090327230902.GG5176@mit.edu> Sender: linux-ext4-owner@vger.kernel.org List-ID: Theodore Tso wrote: > OTOH, the really big databases will tend to use direct I/O, so they > won't be dirtying the page cache anyway. So maybe it's not worth the Not necessarily... From what I understand, a lot of the individual low-level components in cloud storage, such as GoogleFS's chunk server[1] do not bypass the page cache, even though they do care about the details of data caching and data consistency. I am looking at the same areas for my own distributed storage work, and am finding that the current crop of Linux-specific, database/server-friendly syscalls permit more application control over pagecache usage than in past years, decreasing the need for O_DIRECT. Things like readahead(2), sync_file_range(2), fadvise(3), really help. Jeff [1] http://labs.google.com/papers/gfs-sosp2003.pdf