From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx101.postini.com [74.125.245.101]) by kanga.kvack.org (Postfix) with SMTP id 6A0D56B007E for ; Wed, 18 Apr 2012 03:36:36 -0400 (EDT) Received: by vbbey12 with SMTP id ey12so6722963vbb.14 for ; Wed, 18 Apr 2012 00:36:35 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: Date: Wed, 18 Apr 2012 15:36:35 +0800 Message-ID: Subject: Re: how to avoid allocating or freeze MOVABLE memory in userspace From: Haojian Zhuang Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Lameter Cc: linaro-mm-sig@lists.linaro.org, linux-mm@kvack.org, m.szyprowski@samsung.com On Mon, Apr 16, 2012 at 9:55 PM, Christoph Lameter wrote: > On Sat, 14 Apr 2012, Haojian Zhuang wrote: > >> On Sat, Apr 14, 2012 at 2:27 AM, Christoph Lameter wrote: >> > On Fri, 13 Apr 2012, Haojian Zhuang wrote: >> > >> >> I have one question on memory migration. As we know, malloc() from >> >> user app will allocate MIGRATE_MOVABLE pages. But if we want to use >> >> this memory as DMA usage, we can't accept MIGRATE_MOVABLE type. Could >> >> we change its behavior before DMA working? >> > >> > MIGRATE_MOVABLE works fine for DMA. If you keep a reference from a device >> > driver to user pages then you will have to increase the page refcount >> > which will in turn pin the page and make it non movable for as long as you >> > keep the refcount. >> >> Hi Christoph, >> >> Thanks for your illustration. But it's a little abstract. Could you >> give me a simple example >> or show me the code? > > Run get_user_pages() on the memory you are interest in pinning. See how > other drivers do that by looking up other use cases. F.e. ib_umem_get() > does a similar thing. > > Got it. And I think there's conflict in CMA. For example, user process A malloc() memory, page->_count is 1. After using get_user_pages() in device driver for DMA usage, page->_count becomes 2. If the page is in CMA region, it results migrate_pages() returns -EAGAIN. But error handling in CMA is in below. ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA); if (ret == 0) { bitmap_set(cma->bitmap, pageno, count); break; } else if (ret != -EBUSY) { goto error; } Since EAGAIN doesn't equal to EBUSY, dma_alloc_from_contiguous() aborts. Should dma_alloc_from_contiguous() handle EAGAIN? Best Regards Haojian -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org