From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755421AbcFQP7f (ORCPT ); Fri, 17 Jun 2016 11:59:35 -0400 Received: from mga03.intel.com ([134.134.136.65]:26724 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751873AbcFQP7d (ORCPT ); Fri, 17 Jun 2016 11:59:33 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.26,484,1459839600"; d="scan'208";a="1004390031" From: "Huang\, Ying" To: Minchan Kim Cc: "Huang\, Ying" , Andrew Morton , "Kirill A. Shutemov" , Vlastimil Babka , "Jerome Marchand" , Andrea Arcangeli , Ebru Akagunduz , , Subject: Re: [PATCH] MADVISE_FREE, THP: Fix madvise_free_huge_pmd return value after splitting In-Reply-To: <20160617053102.GA2374@bbox> (Minchan Kim's message of "Fri, 17 Jun 2016 14:31:02 +0900") References: <1466132640-18932-1-git-send-email-ying.huang@intel.com> <20160617053102.GA2374@bbox> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) Date: Fri, 17 Jun 2016 08:59:31 -0700 Message-ID: <87inx7lsbg.fsf@yhuang-mobile.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Minchan Kim writes: > Hi, > > On Thu, Jun 16, 2016 at 08:03:54PM -0700, Huang, Ying wrote: >> From: Huang Ying >> >> madvise_free_huge_pmd should return 0 if the fallback PTE operations are >> required. In madvise_free_huge_pmd, if part pages of THP are discarded, >> the THP will be split and fallback PTE operations should be used if >> splitting succeeds. But the original code will make fallback PTE >> operations skipped, after splitting succeeds. Fix that via make >> madvise_free_huge_pmd return 0 after splitting successfully, so that the >> fallback PTE operations will be done. > > You're right. Thanks! > >> >> Know issues: if my understanding were correct, return 1 from >> madvise_free_huge_pmd means the following processing for the PMD should >> be skipped, while return 0 means the following processing is still >> needed. So the function should return 0 only if the THP is split >> successfully or the PMD is not trans huge. But the pmd_trans_unstable >> after madvise_free_huge_pmd guarantee the following processing will be >> skipped for huge PMD. So current code can run properly. But if my >> understanding were correct, we can clean up return code of >> madvise_free_huge_pmd accordingly. > > I like your clean up. Just a minor comment below. > >> >> Signed-off-by: "Huang, Ying" >> --- >> mm/huge_memory.c | 7 +------ >> 1 file changed, 1 insertion(+), 6 deletions(-) >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 2ad52d5..64dc95d 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c > > First of all, let's change ret from int to bool. > And then, add description in the function entry. > > /* > * Return true if we do MADV_FREE successfully on entire pmd page. > * Otherwise, return false. > */ > > And do not set to 1 if it is huge_zero_pmd but just goto out to > return false. Do you want to fold the cleanup with this patch or do that in another patch? Best Regards, Huang, Ying > Thanks! > >> @@ -1655,14 +1655,9 @@ int madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, >> if (next - addr != HPAGE_PMD_SIZE) { >> get_page(page); >> spin_unlock(ptl); >> - if (split_huge_page(page)) { >> - put_page(page); >> - unlock_page(page); >> - goto out_unlocked; >> - } >> + split_huge_page(page); >> put_page(page); >> unlock_page(page); >> - ret = 1; >> goto out_unlocked; >> } >> >> --