From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 5 Nov 2004 05:03:09 +0100 From: Andrea Arcangeli Subject: Re: fix iounmap and a pageattr memleak (x86 and x86-64) Message-ID: <20041105040308.GJ8229@dualathlon.random> References: <418837D1.402@us.ibm.com> <20041103022606.GI3571@dualathlon.random> <418846E9.1060906@us.ibm.com> <20041103030558.GK3571@dualathlon.random> <1099612923.1022.10.camel@localhost> <1099615248.5819.0.camel@localhost> <20041105005344.GG8229@dualathlon.random> <1099619740.5819.65.camel@localhost> <20041105020831.GI8229@dualathlon.random> <1099621391.5819.72.camel@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1099621391.5819.72.camel@localhost> Sender: owner-linux-mm@kvack.org Return-Path: To: Dave Hansen Cc: linux-mm , Linux Kernel Mailing List , Andi Kleen , Andrew Morton List-ID: On Thu, Nov 04, 2004 at 06:23:11PM -0800, Dave Hansen wrote: > I'm not quite sure if this has any other weird effects, so I'll hold on > to it for a week or so and see if anything turns up. this fixed the problem for me too. However I'm not convinced this is correct, nothing in the kernel should ever free a bootmem piece of memory after the machine has booted. If this helps, it also means we found an existing pte (not pmd) with page_count 0 during the first unmap event (bootmem allocated). The transition from mapped to unmapped works fine, but the transition from unmapped to mapped will thorw the pte away and we'll regenerate a 2M pmd where there was a pte instead. I wonder why there are 4k pages there in the first place. Anyways I understand what's going on now thanks to your debugging, and I believe the only real fix is to use PageReserved to catch if we're working on a newly allocated page or not, I don't like to depend on the page_count being 0 for the bootmem pages like the previous code was doing. I believe my code would now fall apart even if you were using it with PSE disabled (nopentium or something). So I've to fix that bit at least and I will use PageReserved for that. The page_count of bootmem pages really doesn't matter since they must never be freed. It really should remain 0 so we catch if anybody executes a put_page on it. I'll fix it up... -- 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: aart@kvack.org