From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751874AbcFTBHS (ORCPT ); Sun, 19 Jun 2016 21:07:18 -0400 Received: from mail-pf0-f193.google.com ([209.85.192.193]:35568 "EHLO mail-pf0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751423AbcFTBHL (ORCPT ); Sun, 19 Jun 2016 21:07:11 -0400 From: Minchan Kim X-Google-Original-From: Minchan Kim Date: Mon, 20 Jun 2016 09:15:19 +0900 To: "Huang, Ying" Cc: Minchan Kim , Andrew Morton , "Kirill A. Shutemov" , Vlastimil Babka , Jerome Marchand , Andrea Arcangeli , Ebru Akagunduz , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] MADVISE_FREE, THP: Fix madvise_free_huge_pmd return value after splitting Message-ID: <20160620001519.GC3194@blaptop> References: <1466132640-18932-1-git-send-email-ying.huang@intel.com> <20160617053102.GA2374@bbox> <87mvmjha54.fsf@yhuang-mobile.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87mvmjha54.fsf@yhuang-mobile.sh.intel.com> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 17, 2016 at 12:45:43PM -0700, Huang, Ying wrote: > 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. > > Yes. bool looks better than int. > > > /* > > * Return true if we do MADV_FREE successfully on entire pmd page. > > * Otherwise, return false. > > */ > > This way, we need to return false if we failed to split huge page, this > will cause unnecessary pmd_trans_unstable check. How about to change > the comments to I focused the function name "madvise_free_huge_pmd". IOW, the function should free huge pmd page. If it is successful, done. Otherwise, next routines should handle it. If it fail to split, pmd_trans_unstable will check it and return. I don't think it's heavy operation to affect performance so rather than making function fast, I wanted to make it simple by following function name. > > /* > * Return true if we finished processing entire pmd page and needn't > * fall back pte processing. Otherwise, return false. > */ > > Best Regards, > Huang, Ying > > > And do not set to 1 if it is huge_zero_pmd but just goto out to > > return false. > > > > 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; > >> } > >> > >> -- > >> 2.8.1 > >> > >> -- > >> 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