From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932571AbcFTPtr (ORCPT ); Mon, 20 Jun 2016 11:49:47 -0400 Received: from mga14.intel.com ([192.55.52.115]:27820 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755102AbcFTPsY (ORCPT ); Mon, 20 Jun 2016 11:48:24 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.26,499,1459839600"; d="scan'208";a="831784062" 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 References: <1466132640-18932-1-git-send-email-ying.huang@intel.com> <20160617053102.GA2374@bbox> <87mvmjha54.fsf@yhuang-mobile.sh.intel.com> <20160620001519.GC3194@blaptop> Date: Mon, 20 Jun 2016 08:48:17 -0700 In-Reply-To: <20160620001519.GC3194@blaptop> (Minchan Kim's message of "Mon, 20 Jun 2016 09:15:19 +0900") Message-ID: <87bn2vamke.fsf@yhuang-mobile.sh.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) 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: > 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. Reasonable. Will do that. Best Regards, Huang, Ying >> >> /* >> * 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