From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id 7ED166B003D for ; Tue, 24 Mar 2009 11:08:41 -0400 (EDT) From: Nick Piggin Subject: Re: why my systems never cache more than ~900 MB? Date: Wed, 25 Mar 2009 02:20:45 +1100 References: <49C89CE0.2090103@wpkg.org> In-Reply-To: <49C89CE0.2090103@wpkg.org> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200903250220.45575.nickpiggin@yahoo.com.au> Sender: owner-linux-mm@kvack.org To: Tomasz Chmielewski Cc: linux-mm@kvack.org List-ID: On Tuesday 24 March 2009 19:42:08 Tomasz Chmielewski wrote: > On my (32 bit) systems with more than 1 GB memory it is impossible to cache > more than about 900 MB. Why? > > Caching never goes beyond ~900 MB (i.e. when I read a mounted drive with > dd): Because blockdev mappings are limited to lowmem due to sharing their cache with filesystem metadata cache, which needs kernel mapped memory. It will >900MB of pagecache data OK (data from regular files) > # free > total used free shared buffers cached > Mem: 2076164 966788 1109376 0 855132 68932 > -/+ buffers/cache: 42724 2033440 > Swap: 2097144 0 2097144 > > > Same behaviour on 32 bit machines with 4 GB RAM. > > No problems on 64 bit machines. > I have one 32 bit machine that caches beyond ~900 MB without problems. Does it have a different user/kernel split? > Is it some kernel/proc/sys setting that I'm missing? No, it just can't be done without changing code. -- 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