From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx156.postini.com [74.125.245.156]) by kanga.kvack.org (Postfix) with SMTP id 398606B0044 for ; Wed, 4 Apr 2012 05:59:09 -0400 (EDT) Received: by bkwq16 with SMTP id q16so102777bkw.14 for ; Wed, 04 Apr 2012 02:59:07 -0700 (PDT) Message-ID: <4F7C1B67.6030300@openvz.org> Date: Wed, 04 Apr 2012 13:59:03 +0400 From: Konstantin Khlebnikov MIME-Version: 1.0 Subject: Re: [PATCH RFC] mm: account VMA before forced-COW via /proc/pid/mem References: <20120402153631.5101.44091.stgit@zurg> <20120403143752.GA5150@redhat.com> In-Reply-To: <20120403143752.GA5150@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Oleg Nesterov Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Hugh Dickins , Andrew Morton , Linus Torvalds Oleg Nesterov wrote: > On 04/02, Konstantin Khlebnikov wrote: >> >> Currently kernel does not account read-only private mappings into memory commitment. >> But these mappings can be force-COW-ed in get_user_pages(). > > Heh. tail -n3 Documentation/vm/overcommit-accounting > may be you should update it then. I just wonder how fragile this accounting... > > Can't really comment the patch, this is not my area. Still, > >> + down_write(&mm->mmap_sem); >> + *pvma = vma = find_vma(mm, addr); >> + if (vma&& vma->vm_start<= addr) { >> + ret = vma->vm_end - addr; >> + if ((vma->vm_flags& (VM_ACCOUNT | VM_NORESERVE | VM_SHARED | >> + VM_HUGETLB | VM_MAYWRITE)) == VM_MAYWRITE) { >> + if (!security_vm_enough_memory_mm(mm, vma_pages(vma))) > > Oooooh, the whole vma. Say, gdb installs the single breakpoint into > the huge .text mapping... We cannot split vma right there, this will be really weird. =) > > I am not sure, but probably you want to check at least VM_IO/PFNMAP > as well. We do not want to charge this memory and retry with FOLL_FORCE > before vm_ops->access(). Say, /dev/mem No, VM_IO/PFNMAP aren't affect accounting, there is VM_NORESERVE for this. > > Hmm. OTOH, if I am right then mprotect_fixup() should be fixed?? mprotect_fixup() does not account area if it already accounted, so all ok. > > > We drop ->mmap_sem... Say, the task does mremap() in between and > len == 2 * PAGE_SIZE. Then, for example, copy_to_user_page() can > write to the same page twice. Perhaps not a problem in practice, > I dunno. I have an old unfinished patch which implements upgrade_read() for rw-semaphore =) > -- 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