From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt To: David Gibson , Cc: "David S. Miller" Subject: Re: consistent_alloc() revisited Date: Sat, 20 Jul 2002 17:28:30 +0200 Message-Id: <20020720152830.1555@192.168.4.1> In-Reply-To: <20020717012442.GA22786@zax> References: <20020717012442.GA22786@zax> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: owner-linuxppc-embedded@lists.linuxppc.org List-Id: >As far as I can tell there's no problem with get_free_pages() (or >rather, alloc_pages()), except that we need to add GFP_ATOMIC to the >flags if we're in interrupt context. > >The problems are in get_vm_area() which does a kmalloc() without >GFP_ATOMIC and in map_page() which can sleep. (Note do DaveM: this thread from linuxppc-embedded talks about out consistent_alloc() functions used to get non-cacheable DMA consistent memory for peripherials on the various non-PCI type busses you can find on such embedded CPUs) We can't rely on in_interrupt(). We can be called with a spinlock held or on the VM path. In those cases, we need GFP_ATOMIC but in_interrupt() won't be set. I would rather pass a gfp_mask argument to consistent_alloc. I know the pci_xxx version lacks that argument, I yet have to talk to DaveM about it, in the meantime, it should be implemented as calling consistent_alloc(..., GFP_ATOMIC). I want the gfp argument to be passed since some drivers will want a quite large pool to be allocated at insmod/kernel init time, and I want to let those drivers to be able to sleep while VM gets the pages back in this case instead of failing as they would probably do with a GFP_ATOMIC on a machine that have been running for some time. Ben. ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/