From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from firewall.hyperwave.com (firewall.hyperwave.com [129.27.200.34]) by kvack.org (8.8.7/8.8.7) with ESMTP id MAA20987 for ; Fri, 28 Aug 1998 12:04:35 -0400 Date: Fri, 28 Aug 1998 18:03:17 +0200 (MET DST) Message-Id: <199808281603.SAA05389@hwal02.hyperwave.com> From: Bernhard Heidegger MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Subject: Re: [PATCH] 498+ days uptime In-Reply-To: References: <199808262153.OAA13651@cesium.transmeta.com> <87ww7v73zg.fsf@atlas.CARNet.hr> <199808271207.OAA15842@hwal02.hyperwave.com> <87emu2zkc0.fsf@atlas.CARNet.hr> <199808271243.OAA28073@hwal02.hyperwave.com> <199808280909.LAA19060@hwal02.hyperwave.com> Sender: owner-linux-mm@kvack.org To: "Eric W. Biederman" Cc: Bernhard Heidegger , Zlatko.Calusic@CARNet.hr, "H. Peter Anvin" , Linux Kernel List , Linux-MM List List-ID: >>>>> ">" == Eric W Biederman writes: >>>> No. Major performance problem. BH> Why? BH> Imagine an application which has most of the (index) file pages in memory BH> and many of the pages are dirty. bdflush will flush the pages regularly, BH> but the pages will get dirty immediately again. BH> If you can be sure, that the power cannot fail the performance should be BH> much better without bdflush, because kflushd has to write pages only if BH> the system is running low on memory... >> The performance improvement comes when looking for free memory. In >> most cases bdflush's slow but steady writing of pages keeps buffers >> clean. When the application wants more memory with bdflush in the >> background unsually the pages it needs will be clean (because the I/O >> started before the application needed it), so they can just be dropped >> out of memory. Relying on kflushd means nothing is written until an >> application needs the memory and then it must wait until something is >> written to disk, which is much slower. >> Further >> a) garanteeing no power failure is hard. Use and UPS and regularly flush/sync the primary data to disk from the application >> b) generally there is so much data on the disk you must write it >> sometime, because you can't hold it all in memory. only a question of how much RAM you can put in your PC >> c) I have trouble imagining a case where a small file would be rewritten >> continually. Not really small, but a database application may use btree based indexes, where many blocks will get dirty when inserting/deleting data. If you flush the dirty buffers and the next insertion dirty the same buffer(s) you have lost performance (Note: the btree based indexes are secondary data; you can rebuild it from scratch if the system fails) Bernhard get my pgp key from a public keyserver (keyID=0x62446355) ----------------------------------------------------------------------------- Bernhard Heidegger bheide@hyperwave.com Hyperwave Software Research & Development Schloegelgasse 9/1, A-8010 Graz Voice: ++43/316/820918-25 Fax: ++43/316/820918-99 ----------------------------------------------------------------------------- -- This is a majordomo managed list. To unsubscribe, send a message with the body 'unsubscribe linux-mm me@address' to: majordomo@kvack.org