From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io1-f71.google.com (mail-io1-f71.google.com [209.85.166.71]) by kanga.kvack.org (Postfix) with ESMTP id CB4818E0001 for ; Wed, 26 Sep 2018 10:52:00 -0400 (EDT) Received: by mail-io1-f71.google.com with SMTP id w19-v6so52247862ioa.10 for ; Wed, 26 Sep 2018 07:52:00 -0700 (PDT) Received: from userp2130.oracle.com (userp2130.oracle.com. [156.151.31.86]) by mx.google.com with ESMTPS id w6-v6si3253284ioc.44.2018.09.26.07.51.59 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 26 Sep 2018 07:51:59 -0700 (PDT) Date: Wed, 26 Sep 2018 07:51:45 -0700 From: Daniel Jordan Subject: Re: [PATCH -V5 RESEND 03/21] swap: Support PMD swap mapping in swap_duplicate() Message-ID: <20180926145145.6xp2kxpngyd54f6i@ca-dmjordan1.us.oracle.com> References: <20180925071348.31458-1-ying.huang@intel.com> <20180925071348.31458-4-ying.huang@intel.com> <20180925191953.4ped5ki7u3ymafmd@ca-dmjordan1.us.oracle.com> <874lecifj4.fsf@yhuang-dev.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <874lecifj4.fsf@yhuang-dev.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Huang, Ying" Cc: Daniel Jordan , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" , Andrea Arcangeli , Michal Hocko , Johannes Weiner , Shaohua Li , Hugh Dickins , Minchan Kim , Rik van Riel , Dave Hansen , Naoya Horiguchi , Zi Yan On Wed, Sep 26, 2018 at 08:55:59PM +0800, Huang, Ying wrote: > Daniel Jordan writes: > > On Tue, Sep 25, 2018 at 03:13:30PM +0800, Huang Ying wrote: > >> /* > >> * Increase reference count of swap entry by 1. > >> - * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required > >> - * but could not be atomically allocated. Returns 0, just as if it succeeded, > >> - * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which > >> - * might occur if a page table entry has got corrupted. > >> + * > >> + * Return error code in following case. > >> + * - success -> 0 > >> + * - swap_count_continuation is required but could not be atomically allocated. > >> + * *entry is used to return swap entry to call add_swap_count_continuation(). > >> + * -> ENOMEM > >> + * - otherwise same as __swap_duplicate() > >> */ > >> -int swap_duplicate(swp_entry_t entry) > >> +int swap_duplicate(swp_entry_t *entry, int entry_size) > >> { > >> int err = 0; > >> > >> - while (!err && __swap_duplicate(entry, 1) == -ENOMEM) > >> - err = add_swap_count_continuation(entry, GFP_ATOMIC); > >> + while (!err && > >> + (err = __swap_duplicate(entry, entry_size, 1)) == -ENOMEM) > >> + err = add_swap_count_continuation(*entry, GFP_ATOMIC); > >> return err; > > > > Now we're returning any error we get from __swap_duplicate, apparently to > > accommodate ENOTDIR later in the series, which is a change from the behavior > > introduced in 570a335b8e22 ("swap_info: swap count continuations"). This might > > belong in a separate patch given its potential for side effects. > > I have checked all the calls of the function and found there will be no > bad effect. Do you have any side effect? Before I was just being vaguely concerned about any unintended side effects, but looking again, yes I do. Now when swap_duplicate returns an error in copy_one_pte, copy_one_pte returns a (potentially nonzero) entry.val, which copy_pte_range interprets unconditionally as 'try adding a swap count continuation.' Not what we want for returns other than -ENOMEM. So it might make sense to have a separate patch that changes swap_duplicate's return and makes callers handle it.