From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id 1131F6B004A for ; Tue, 30 Nov 2010 18:32:57 -0500 (EST) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit From: Roland McGrath Subject: Re: Flushing whole page instead of work for ptrace In-Reply-To: Michal Simek's message of Friday, 26 November 2010 13:31:42 +0100 <4CEFA8AE.2090804@petalogix.com> References: <4CEFA8AE.2090804@petalogix.com> Message-Id: <20101130233250.35603401C8@magilla.sf.frob.com> Date: Tue, 30 Nov 2010 15:32:50 -0800 (PST) Sender: owner-linux-mm@kvack.org To: michal.simek@petalogix.com Cc: Oleg Nesterov , Andrew Morton , LKML , linux-mm@kvack.org, John Williams , "Edgar E. Iglesias" List-ID: This is a VM question more than a ptrace question. I can't give you any authoritative answers about the VM issues. Documentation/cachetlb.txt says: Any time the kernel writes to a page cache page, _OR_ the kernel is about to read from a page cache page and user space shared/writable mappings of this page potentially exist, this routine is called. In your case, the kernel is only reading (write=0 passed to access_process_vm and get_user_pages). In normal situations, the page in question will have only a private and read-only mapping in user space. So the call should not be required in these cases--if the code can tell that's so. Perhaps something like the following would be safe. But you really need some VM folks to tell you for sure. diff --git a/mm/memory.c b/mm/memory.c index 02e48aa..2864ee7 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1484,7 +1484,8 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, pages[i] = page; flush_anon_page(vma, page, start); - flush_dcache_page(page); + if ((vm_flags & VM_WRITE) || (vma->vm_flags & VM_SHARED) + flush_dcache_page(page); } if (vmas) vmas[i] = vma; Thanks, Roland -- 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 policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org