From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <46CE7211.2010708@redhat.com> Date: Fri, 24 Aug 2007 01:52:17 -0400 From: Chris Snook MIME-Version: 1.0 Subject: Re: Drop caches - is this safe behavior? References: <46CE3617.6000708@redhat.com> <1187930857.6406.12.camel@norville.austin.ibm.com> <46CE69DE.9040807@redhat.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: mike Cc: Dave Kleikamp , linux-mm@kvack.org List-ID: mike wrote: > On 8/23/07, Chris Snook wrote: >> Mike -- >> >> Try Dave's suggestion to increase vm.vfs_cache_pressure. drop_pages >> should never be needed, regardless of which caches you're dropping. >> >> -- Chris >> > > thanks all. i will try it on one of the machines and see how it performs. > > this is an opteron 1.8ghz (amd64), ubuntu, latest stable linux kernel, > 3 gigs of ram (just FYI) - SATA disk. > > i thought i'd do it every 5 minutes not because of a horrible memory > leak that fast, but figured "why not just free up all RAM as often as > possible" I think the caches you had in mind were the ones that would be dropped by echoing '1' into /proc/sys/vm/drop_caches, not the ones that would be dropped by echoing '2' into it. If you were dropping pagecache every five minutes, it would kill your performance as you described. As for the question of safety, '3' should also be safe, but terrible for performance, as it does all the harm of '1', plus some. > when you said "sar" are you talking about this: > > atsar - system activity reporter > Description: system activity reporter > Monitor system resources such as CPU, network, memory & disk I/O, and > record data for later analysis I'm not familiar with the "atsar" implementation, but it appears to be an alternate implementation of the same thing. It's an excellent tool for long-term workload profiling. -- Chris -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org