From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alan Cox Subject: Re: kernel addresses Date: 28 Oct 2002 23:26:14 +0000 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <1035847574.3550.109.camel@irongate.swansea.linux.org.uk> References: <20021028230140.79410.qmail@web80305.mail.yahoo.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20021028230140.79410.qmail@web80305.mail.yahoo.com> List-Id: linux-scsi@vger.kernel.org To: Mark Lobo Cc: linux-scsi@vger.kernel.org kmalloc memory comes out of the pool requested GFP_DMA selects the ISA space, GFP_HIGH allows all 36bits (if I remember rightly). vmalloc comes from the whole of memory space. the highmem I/O stuff is a 2.4 patch some people use so that DMA aware drivers that support the full 32bit DMA range can avoid bounce buffers. This comes from a 2.4 transition thing. Older drivers assume memory they access is always mapped (eg when doing PIO) so the scsi code makes sure this is true. The bounce patch lets drivers that don't do PIO avoid this. 2.5 does the job properly instead as part of the block rewrite