From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yb1-f199.google.com (mail-yb1-f199.google.com [209.85.219.199]) by kanga.kvack.org (Postfix) with ESMTP id 35C708E00A4 for ; Tue, 25 Sep 2018 15:20:11 -0400 (EDT) Received: by mail-yb1-f199.google.com with SMTP id v1-v6so10663670ybk.22 for ; Tue, 25 Sep 2018 12:20:11 -0700 (PDT) Received: from userp2130.oracle.com (userp2130.oracle.com. [156.151.31.86]) by mx.google.com with ESMTPS id t6-v6si329055ywd.201.2018.09.25.12.20.09 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 25 Sep 2018 12:20:10 -0700 (PDT) Date: Tue, 25 Sep 2018 12:19:53 -0700 From: Daniel Jordan Subject: Re: [PATCH -V5 RESEND 03/21] swap: Support PMD swap mapping in swap_duplicate() Message-ID: <20180925191953.4ped5ki7u3ymafmd@ca-dmjordan1.us.oracle.com> References: <20180925071348.31458-1-ying.huang@intel.com> <20180925071348.31458-4-ying.huang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180925071348.31458-4-ying.huang@intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: Huang Ying Cc: 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 , Daniel Jordan On Tue, Sep 25, 2018 at 03:13:30PM +0800, Huang Ying wrote: > @@ -3487,35 +3521,66 @@ static int __swap_duplicate_locked(struct swap_info_struct *p, > } > > /* > - * Verify that a swap entry is valid and increment its swap map count. > + * Verify that the swap entries from *entry is valid and increment their > + * PMD/PTE swap mapping count. > * > * Returns error code in following case. > * - success -> 0 > * - swp_entry is invalid -> EINVAL > - * - swp_entry is migration entry -> EINVAL I'm assuming it wasn't possible to hit this error before this patch, and you're just removing it now since you're in the area? > * - swap-cache reference is requested but there is already one. -> EEXIST > * - swap-cache reference is requested but the entry is not used. -> ENOENT > * - swap-mapped reference requested but needs continued swap count. -> ENOMEM > + * - the huge swap cluster has been split. -> ENOTDIR Strangely intuitive choice of error code :) > /* > * 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. Although, I don't understand why 570a335b8e22 ignored errors other than -ENOMEM when both swap_duplicate callers _seem_ from a quick read to be able to respond gracefully to any error.