From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: vDSO vs. mm : problems with ppc vdso From: Benjamin Herrenschmidt In-Reply-To: <20060227215416.2bfc1e18.akpm@osdl.org> References: <1141105154.3767.27.camel@localhost.localdomain> <20060227215416.2bfc1e18.akpm@osdl.org> Content-Type: text/plain Date: Tue, 28 Feb 2006 17:08:16 +1100 Message-Id: <1141106896.3767.34.camel@localhost.localdomain> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: linux-mm@kvack.org, hugh@veritas.com, paulus@samba.org, nickpiggin@yahoo.com.au, "David S. Miller" List-ID: > As mentioned on IRC, we keep on getting bugs because we don't have a clear > separation between 64-bit tasks (a task_struct thing) and 64-bit mm's (an > mm_struct thing). I'd propose added mm_struct.task_size and testing that > in the appropriate places. Ok, What about a patch adding mm->task_size and setting it to TASK_SIZE asap and use that to fix my bug at least. It would have to be done in flush_old_exec(), after the call to flush_thread() at least on powerpc that's where we properly switch the TIF_32BIT flag. I can't do it earlier. Does that sound all right ? I'll send the patch as a reply to this message. > > The second problem is more subtle and that's where I really need a VM > > guru to help me assess how bad the situation is and what should be done > > to fix it. > > > > Since when not-COWed, those vDSO pages are actually kernel pages mapped > > into every process, they aren't per-se anonymous pages, nor file > > pages... in fact, they don't quite fit in anything rmap knows about. > > However, I can't mark the VMA as VM_RESERVED or anything like that since > > that would prevent COW from working. > > > > Thus we hit some "interesting" code path in rmap of that sort: > > rmap won't touch this page unless your ->nopage handler put it onto the > page LRU. It indeed looks like try_to_unmap() is never called if page->mapping is NULL. Do you gus see any other case where my "special" vma & those kernel pages in could be a problem ? Cheers, Ben. -- 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