From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: vm_ops.page_mkwrite() fails with vmalloc on 2.6.23 From: Peter Zijlstra In-Reply-To: <1193681839.27652.60.camel@twins> References: <1193064057.16541.1.camel@matrix> <20071029004002.60c7182a.akpm@linux-foundation.org> <45a44e480710290117u492dbe82ra6344baf8bb1e370@mail.gmail.com> <1193677302.27652.56.camel@twins> <45a44e480710291051s7ffbb582x64ea9524c197b48a@mail.gmail.com> <1193681839.27652.60.camel@twins> Content-Type: text/plain Date: Mon, 29 Oct 2007 23:16:50 +0100 Message-Id: <1193696211.5644.100.camel@lappy> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Jaya Kumar Cc: Andrew Morton , stefani@seibold.net, linux-kernel@vger.kernel.org, David Howells , linux-mm@kvack.org, Hugh Dickins List-ID: On Mon, 2007-10-29 at 19:17 +0100, Peter Zijlstra wrote: > On Mon, 2007-10-29 at 13:51 -0400, Jaya Kumar wrote: > > On 10/29/07, Peter Zijlstra wrote: > > > On Mon, 2007-10-29 at 01:17 -0700, Jaya Kumar wrote: > > > > An aside, I just tested that deferred IO works fine on 2.6.22.10/pxa255. > > > > > > > > I understood from the thread that PeterZ is looking into page_mkclean > > > > changes which I guess went into 2.6.23. I'm also happy to help in any > > > > way if the way we're doing fb_defio needs to change. > > > > > > OK, seems I can't read. Or at least, I missed a large part of the > > > problem. > > > > > > page_mkclean() hasn't changed, it was ->page_mkwrite() that changed. And > > > looking at the fb_defio code, I'm not sure I understand how its > > > page_mkclean() use could ever have worked. > > > > > > The proposed patch [1] only fixes the issue of ->page_mkwrite() on > > > vmalloc()'ed memory. Not page_mkclean(), and that has never worked from > > > what I can make of it. > > > > > > Jaya, could you shed some light on this? I presume you had your display > > > working. > > > > > > > I thought I had it working. I saw the display update after each > > mmap/write sequence to the framebuffer. I need to check if there's an > > munmap or anything else going on in between write sequences that would > > cause it to behave like page_mkclean was working. > > > > Is it correct to assume that page_mkclean should mark the pages > > read-only so that the next write would again trigger mkwrite? > > Well, yes, that is the intended behaviour. > > > Even if the page was from a vmalloc_to_page()? > > That is the crux, I only ever implemented it for file pages. Hmm, so these vmalloc pages are mapped into user-space with remap_pfn_range(), which doesn't have any form of rmap. That is, given a pfn there is no way to obtain all ptes for it. So the interface to page_mkclean() could never work for these (as it only provides a struct page *). [ also, remap_vmalloc_range() suffers similar issues, only file and anon have proper rmap ] I'm not sure we want full rmap for remap_pfn/vmalloc_range, but perhaps we could assist drivers in maintaining and using vma lists. I think page_mkclean_one() would work if you'd manually set page->index and iterate the vmas yourself. Although atm I'm not sure of anything so don't pin me on it. -- 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