From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pb0-f54.google.com (mail-pb0-f54.google.com [209.85.160.54]) by kanga.kvack.org (Postfix) with ESMTP id 69D996B00A8 for ; Wed, 13 Nov 2013 02:13:42 -0500 (EST) Received: by mail-pb0-f54.google.com with SMTP id ro12so5025925pbb.41 for ; Tue, 12 Nov 2013 23:13:42 -0800 (PST) Received: from psmtp.com ([74.125.245.206]) by mx.google.com with SMTP id cj2si22428207pbc.207.2013.11.12.23.13.39 for ; Tue, 12 Nov 2013 23:13:40 -0800 (PST) Message-ID: <52832724.1090000@asianux.com> Date: Wed, 13 Nov 2013 15:15:48 +0800 From: Chen Gang MIME-Version: 1.0 Subject: Re: [PATCH] mm: revert mremap pud_free anti-fix References: <525D2B15.8060503@asianux.com> In-Reply-To: <525D2B15.8060503@asianux.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org On 10/15/2013 07:46 PM, Chen Gang wrote: > On 10/15/2013 06:34 PM, Hugh Dickins wrote: >> > Revert 1ecfd533f4c5 ("mm/mremap.c: call pud_free() after fail calling >> > pmd_alloc()"). The original code was correct: pud_alloc(), pmd_alloc(), >> > pte_alloc_map() ensure that the pud, pmd, pt is already allocated, and >> > seldom do they need to allocate; on failure, upper levels are freed if >> > appropriate by the subsequent do_munmap(). Whereas 1ecfd533f4c5 did an >> > unconditional pud_free() of a most-likely still-in-use pud: saved only >> > by the near-impossiblity of pmd_alloc() failing. >> > > What you said above sounds reasonable to me, but better to provide the > information below: > > - pud_free() for pgd_alloc() in "arch/arm/mm/pgd.c". > It is correct, it is for 'new_pgd' which not come from 'mm'. > - pud_free() for init_stub_pte() in "arch/um/kernel/skas/mmu.c". > For me, it need improvement, I have sent related patch for it. > - more details about do_munmap(), (e.g. do it need mm->page_table_lock) > or more details about the demo "most-likely still-in-use pud ...". > According to "Documentation/vm/locking", 'mm->page_table_lock' is for using vma list, so not need it when its related vmas are detached from using vma list. The related work flow: do_munmap()-> detach_vmas_to_be_unmapped(); /* so not need mm->page_table_lock */ unmap_region() -> free_pgtables() -> free_pgd_range() -> free_pud_range() -> free_pmd_range() -> free_pte_range() -> pmd_clear(); pte_free_tlb(); pud_clear(); pmd_free_tlb(); pgd_clear(); pud_free_tlb(); Thanks. > > Hmm... I am not quite sure about the 3 things, and I will/should > continue analysing/learning about them, but better to get your reply. :-) -- Chen Gang -- 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