From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B0A04C4363D for ; Tue, 22 Sep 2020 07:11:35 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id CD9B721924 for ; Tue, 22 Sep 2020 07:11:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="fd9UV+iK" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CD9B721924 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=nvidia.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 2768B6B00D3; Tue, 22 Sep 2020 03:11:34 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2012E6B00D4; Tue, 22 Sep 2020 03:11:34 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1153F6B00D6; Tue, 22 Sep 2020 03:11:34 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0192.hostedemail.com [216.40.44.192]) by kanga.kvack.org (Postfix) with ESMTP id E7A936B00D3 for ; Tue, 22 Sep 2020 03:11:33 -0400 (EDT) Received: from smtpin27.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id DE1B61EF1 for ; Tue, 22 Sep 2020 07:11:32 +0000 (UTC) X-FDA: 77289826824.27.mice78_62062042714b Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin27.hostedemail.com (Postfix) with ESMTP id B629D3D670 for ; Tue, 22 Sep 2020 07:11:32 +0000 (UTC) X-HE-Tag: mice78_62062042714b X-Filterd-Recvd-Size: 5267 Received: from hqnvemgate25.nvidia.com (hqnvemgate25.nvidia.com [216.228.121.64]) by imf01.hostedemail.com (Postfix) with ESMTP for ; Tue, 22 Sep 2020 07:11:31 +0000 (UTC) Received: from hqmail.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate25.nvidia.com (using TLS: TLSv1.2, AES256-SHA) id ; Tue, 22 Sep 2020 00:10:44 -0700 Received: from [10.2.52.174] (10.124.1.5) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Tue, 22 Sep 2020 07:11:30 +0000 Subject: Re: [PATCH 3/5] mm: Rework return value for copy_one_pte() To: Peter Xu , , CC: Jason Gunthorpe , Andrew Morton , Jan Kara , Michal Hocko , Kirill Tkhai , Kirill Shutemov , Hugh Dickins , Christoph Hellwig , Andrea Arcangeli , Oleg Nesterov , Leon Romanovsky , Linus Torvalds , "Jann Horn" References: <20200921211744.24758-1-peterx@redhat.com> <20200921211744.24758-4-peterx@redhat.com> From: John Hubbard Message-ID: <6eb46d4d-8267-4e10-0157-e2ce2be2850d@nvidia.com> Date: Tue, 22 Sep 2020 00:11:29 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20200921211744.24758-4-peterx@redhat.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL111.nvidia.com (172.20.187.18) To HQMAIL107.nvidia.com (172.20.187.13) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1600758644; bh=8J71hRtGdhJ0Jg8YwjuNNAFNeiVmfi98qQdLTq8Xlvc=; h=Subject:To:CC:References:From:Message-ID:Date:User-Agent: MIME-Version:In-Reply-To:Content-Type:Content-Language: Content-Transfer-Encoding:X-Originating-IP:X-ClientProxiedBy; b=fd9UV+iK4layuQDHkfCQ0DfdIT0PjMADSSkh0YkG8MJXBIPzOodb/mgiW9vQGHQBi rQ/2VftVeE/Dp6XoRpkgndJKAXocZAZb44nTXMVdcjO1mSlXbXLw+Vu+kgB12PlaJP 1GMip8RM86OZQUiZ2QUw92xRf929bxNx1UYc1eobvtyt7AitupF54FwjJQ1D4YuHt6 WyZs6WglqEciB/S8MXi2BCH8Vs9cRrpsdRtzvyY917NrN2qs2HBEGBdL4mDkTgt64u mYzm6asnaANurCWu77r/dSbYG/xuyPbDuBpT+5TJzE2vlrlsDle1VMRp+Da5xu/dvH z+6/jh35EVZgQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 9/21/20 2:17 PM, Peter Xu wrote: > There's one special path for copy_one_pte() with swap entries, in which > add_swap_count_continuation(GFP_ATOMIC) might fail. In that case we'll return I might be looking at the wrong place, but the existing code seems to call add_swap_count_continuation(GFP_KERNEL), not with GFP_ATOMIC? > the swp_entry_t so that the caller will release the locks and redo the same > thing with GFP_KERNEL. > > It's confusing when copy_one_pte() must return a swp_entry_t (even if all the > ptes are non-swap entries). More importantly, we face other requirement to > extend this "we need to do something else, but without the locks held" case. > > Rework the return value into something easier to understand, as defined in enum > copy_mm_ret. We'll pass the swp_entry_t back using the newly introduced union I like the documentation here, but it doesn't match what you did in the patch. Actually, the documentation had the right idea (enum, rather than #define, for COPY_MM_* items). Below... > copy_mm_data parameter. > > Another trivial change is to move the reset of the "progress" counter into the > retry path, so that we'll reset it for other reasons too. > > This should prepare us with adding new return codes, very soon. > > Signed-off-by: Peter Xu > --- > mm/memory.c | 42 +++++++++++++++++++++++++++++------------- > 1 file changed, 29 insertions(+), 13 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 7525147908c4..1530bb1070f4 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -689,16 +689,24 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr, > } > #endif > > +#define COPY_MM_DONE 0 > +#define COPY_MM_SWAP_CONT 1 Those should be enums, so as to get a little type safety and other goodness from using non-macro items. ... > @@ -866,13 +877,18 @@ static int copy_pte_range(struct mm_struct *dst_mm, struct mm_struct *src_mm, > pte_unmap_unlock(orig_dst_pte, dst_ptl); > cond_resched(); > > - if (entry.val) { > - if (add_swap_count_continuation(entry, GFP_KERNEL) < 0) > + switch (copy_ret) { > + case COPY_MM_SWAP_CONT: > + if (add_swap_count_continuation(data.entry, GFP_KERNEL) < 0) > return -ENOMEM; > - progress = 0; Yes. Definitely a little cleaner to reset this above, instead of here. > + break; > + default: > + break; I assume this no-op noise is to placate the compiler and/or static checkers. :) I'm unable to find any actual problems with the diffs, aside from the nit about using an enum. thanks, -- John Hubbard NVIDIA