Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E7410C433EF for ; Tue, 16 Nov 2021 04:22:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BC79A61B30 for ; Tue, 16 Nov 2021 04:22:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344324AbhKPEZH (ORCPT ); Mon, 15 Nov 2021 23:25:07 -0500 Received: from mail.kernel.org ([198.145.29.99]:53678 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343880AbhKPEYr (ORCPT ); Mon, 15 Nov 2021 23:24:47 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 7955761B30; Tue, 16 Nov 2021 04:21:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1637036509; bh=wwMatGyZhfNZCPaF2wvkt3Y+SqGCuP8mHGMgs8mAL/4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=T2x+VpryqG7dLunHOg0FxA+cB/ng41qGTKGrA388DL79Mj3eHRBK1hI0sYQ8hwGz1 +UtyE5qGG9t/Go2NA7CkTZ1dbsPVzkUffu1jQVSE6vQ9r5Ybs5QQIqScZ/fj4rZPkt jLW6Ea+GFqIT/+zaXGcWVPpiRxyANwq4LFHzMopM= Date: Mon, 15 Nov 2021 20:21:46 -0800 From: Andrew Morton To: Baolin Wang Cc: ziy@nvidia.com, shy828301@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/3] mm: migrate: Correct the hugetlb migration stats Message-Id: <20211115202146.473fff2404d7fb200dd48bd3@linux-foundation.org> In-Reply-To: <71a4b6c22f208728fe8c78ad26375436c4ff9704.1636275127.git.baolin.wang@linux.alibaba.com> References: <71a4b6c22f208728fe8c78ad26375436c4ff9704.1636275127.git.baolin.wang@linux.alibaba.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 7 Nov 2021 16:57:26 +0800 Baolin Wang wrote: > Correct the migration stats for hugetlb with using compound_nr() instead > of thp_nr_pages(), It would be helpful to explain why using thp_nr_pages() was wrong. And to explain the end user visible effects of this bug so we can decide whether -stable backporting is desirable. > meanwhile change 'nr_failed_pages' to record the > number of normal pages failed to migrate, including THP and hugetlb, > and 'nr_succeeded' will record the number of normal pages migrated > successfully. > > Reviewed-by: Zi Yan > Signed-off-by: Baolin Wang > --- > mm/migrate.c | 17 ++++++++--------- > 1 file changed, 8 insertions(+), 9 deletions(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index 9aafdab..756190b 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1436,9 +1436,9 @@ static inline int try_split_thp(struct page *page, struct page **page2, > * It is caller's responsibility to call putback_movable_pages() to return pages > * to the LRU or free list only if ret != 0. > * > - * Returns the number of {normal page, THP} that were not migrated, or an error code. > - * The number of THP splits will be considered as the number of non-migrated THP, > - * no matter how many subpages of the THP are migrated successfully. > + * Returns the number of {normal page, THP, hugetlb} that were not migrated, or This is a bit confusing. If migrate_pages() failed to migrate one 4k pages then it returns 1, yes? But if migrate_pages() fails to migrate one 2MB hugepage then will it return 1 or will it return 512? And how can the caller actually _use_ this return value without knowing the above information? In other words, perhaps this function should simply return pass/fail?