From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tomasz Chmielewski Subject: does SCSI eat my PC's memory? Date: Mon, 12 Feb 2007 11:08:46 +0100 Message-ID: <45D03CAE.8050205@wpkg.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-2; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail.syneticon.net ([213.239.212.131]:43415 "EHLO mail2.syneticon.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964849AbXBLKhV (ORCPT ); Mon, 12 Feb 2007 05:37:21 -0500 Received: from localhost (localhost [127.0.0.1]) by mail2.syneticon.net (Postfix) with ESMTP id 7769053CDB for ; Mon, 12 Feb 2007 11:09:13 +0100 (CET) Received: from mail2.syneticon.net ([127.0.0.1]) by localhost (linux [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 07649-04 for ; Mon, 12 Feb 2007 11:08:50 +0100 (CET) Received: from postfix1.syneticon.net (postfix1.syneticon.net [192.168.112.6]) by mail2.syneticon.net (Postfix) with ESMTP for ; Mon, 12 Feb 2007 11:08:50 +0100 (CET) Received: from localhost (filter1.syneticon.net [192.168.113.3]) by postfix1.syneticon.net (Postfix) with ESMTP id B77D393E1 for ; Mon, 12 Feb 2007 11:08:51 +0100 (CET) Received: from postfix1.syneticon.net ([192.168.113.4]) by localhost (192.168.113.3 [192.168.113.3]) (amavisd-new, port 10025) with ESMTP id yFkD1RrJZ6xj for ; Mon, 12 Feb 2007 11:08:49 +0100 (CET) Received: from [81.173.182.160] (xdsl-81-173-182-160.netcologne.de [81.173.182.160]) by postfix1.syneticon.net (Postfix) with ESMTP for ; Mon, 12 Feb 2007 11:08:49 +0100 (CET) Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: linux-scsi@vger.kernel.org Does SCSI eat my PC's memory? Probably not, but I can't find an explanation of what uses so much RAM when I use SCSI disks. A little background first. Overall, the system has 1 GB memory. When it boots and everything has started, about 60 MB of memory is used (excluding buffers). One partition is on a iSCSI target (I access it using open-iscsi): /dev/sda 570G 402G 139G 75% /mnt/iscsi_backup It contains lots of data, many files, hardlinked multiple times (in total, almost 100 000 000 files). When I run "find /mnt/iscsi_backup" for some time, and run "free" to see memory usage, I can see almost 500 MB is used (excluding buffers/cache): # free total used free shared buffers cached Mem: 1048576 1029360 19216 0 530972 17628 -/+ buffers/cache: 480760 567816 Swap: 1048568 68 1048500 Also, stopping all deamons and dropping cache doesn't help (sum of the memory used by all processes, displayed by "ps", is about 60 MB): # echo 1 > /proc/sys/vm/drop_caches # free total used free shared buffers cached Mem: 1048576 453932 594644 0 352 6408 -/+ buffers/cache: 447172 601404 Swap: 1048568 68 1048500 A single "umount" command releases almost 400 MB of memory: # umount /mnt/iscsi_backup/ # free total used free shared buffers cached Mem: 1048576 64188 984388 0 232 6528 -/+ buffers/cache: 57428 991148 Swap: 1048568 64 1048504 What used almost 400 MB? SCSI buffers? I can't find any documentation on that. I noticed that when I add RAM to the system, more "unexplained" RAM will be used. When I remove some RAM (i.e. so that the system has 512 MB), "unexplained" RAM usage will drop - as a rule of thumb, I observed that about 50% of RAM is used by something I can't identify. -- Tomasz Chmielewski http://wpkg.org