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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 0EFF0CD37B9 for ; Mon, 11 May 2026 12:17:22 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7194A6B00C9; Mon, 11 May 2026 08:17:21 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6F0A56B00CB; Mon, 11 May 2026 08:17:21 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 62E6F6B00CC; Mon, 11 May 2026 08:17:21 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 51DCC6B00C9 for ; Mon, 11 May 2026 08:17:21 -0400 (EDT) Received: from smtpin24.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 0ADB0A06D8 for ; Mon, 11 May 2026 12:17:21 +0000 (UTC) X-FDA: 84755039082.24.8AF4881 Received: from out-184.mta0.migadu.com (out-184.mta0.migadu.com [91.218.175.184]) by imf16.hostedemail.com (Postfix) with ESMTP id 65B6F180011 for ; Mon, 11 May 2026 12:17:17 +0000 (UTC) Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=cl9hhl9W; spf=pass (imf16.hostedemail.com: domain of baoquan.he@linux.dev designates 91.218.175.184 as permitted sender) smtp.mailfrom=baoquan.he@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1778501839; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=v1Xtp8ucmwoascdJlTfCMmSV9tphy+hPG1tbhbr9z9U=; b=WI1OiM+AXXNmW9IoABeRCkfy6RcvpiBKT/yXi4U+fNop6L11Q+tlKkvO20ns2CywZKYAr8 YWqPudk+YvgYHJNhDF3wy9BUm0oS5ak/QFtSnSiJjhV2R0+W4otOV8lNU2s5zaSlG5wMnw CaQ6dYOcKFdneYT9hl40fjkHh68jzVw= ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=cl9hhl9W; spf=pass (imf16.hostedemail.com: domain of baoquan.he@linux.dev designates 91.218.175.184 as permitted sender) smtp.mailfrom=baoquan.he@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1778501839; a=rsa-sha256; cv=none; b=1O/7JwJNx/oI5NUFpPFc8fPwmNJEpbPA43vnN0RjJ/Xi8wmzbVYzd1y40REfCpmCHu647R VJ1g3Ivd29twsD5ZgQRsYXxLj71t+ZK1NWNwPHkiRmtmp+9hvx86lCGFsKrBM5cUFe1fAb fKoj7R/64qaEUs3ueYbrOzsoDpGDODA= Date: Mon, 11 May 2026 20:17:00 +0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1778501832; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=v1Xtp8ucmwoascdJlTfCMmSV9tphy+hPG1tbhbr9z9U=; b=cl9hhl9WX0F98pNQ5NWV5bfqT4tkm9/T2whpttx3jOkdzKxo0+X4UaferwfKdYD7MtUH7c Mj2H6Ox9046KWDIPYwPgc+/f8hoJXB/HkCDG0jzIgovKQuf9kOBuqfJkaMYV0e3oZ2HcKf lrDUKdDNIoPx72mrTRKSFvQPXHLyyyc= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Baoquan He To: Kairui Song Cc: linux-mm@kvack.org, akpm@linux-foundation.org, usama.arif@linux.dev, chrisl@kernel.org, baohua@kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, youngjun.park@lge.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 2/3] mm/swap: use swap_ops to register swap device's methods Message-ID: References: <20260511073334.635682-1-baoquan.he@linux.dev> <20260511073334.635682-3-baoquan.he@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 65B6F180011 X-Stat-Signature: y59h1nja47zzd3ygcq8bz4mstan6yo6f X-HE-Tag: 1778501837-668698 X-HE-Meta: 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 1xaPztxI SbSmOwyyLF4+bLvTP5A45Osdfr+xQckfFHnWEDJtlQCg0VeerYojcE4vmM/GG0r/OxFHHey+6iH7L/VQ2gb8ZLFwA7ZiwNiC+ZYr7S5uVDRniDUEAiq5DsH9T/obuwr+3skCMN1wKKF9ezv61f6ERz+7K2jAXZMmvqLUM7OJa8a4fonMOuMwhr+VdhhnD5EeUsQ7f+FxlN+SKfEtH5KgNclrSdovqUMNYUxpuGDLO8/9GLYxbIbJ7g50LXEFciesTwT4mTqH7jbv4Nq6H4KSYdsN2xH4hqTKr3dsAAI7zPjaHKLLkWyLbcw37uoMt0Pl7hWwv Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 05/11/26 at 04:37pm, Kairui Song wrote: > On Mon, May 11, 2026 at 3:43 PM Baoquan He wrote: > > > > This simplifies codes and makes logic clearer. And also makes later any > > new swap device type being added easier to handle. > > > > Currently there are three types of swap devices: bdev_fs, bdev_sync > > and bdev_async, and only operations read_folio and write_folio are > > included. In the future, there could be more swap device types added > > and more appropriate opeations adapted into swap_ops. > > Hi Baoquan, > > Thanks for the patch. Sorry I was busy with travel and a few other > series and didn't got a chance to look at a few previous versions. > > > +struct swap_ops { > > + void (*read_folio)(struct swap_info_struct *sis, > > + struct folio *folio, > > + struct swap_iocb **plug); > > + void (*write_folio)(struct swap_info_struct *sis, > > + struct folio *folio, > > + struct swap_iocb **plug); > > +}; > > Overall, I really like this idea, we can have a cleaner interface > starting there. > > > diff --git a/mm/swapfile.c b/mm/swapfile.c > > index 9174f1eeffb0..82d2c9b35b11 100644 > > --- a/mm/swapfile.c > > +++ b/mm/swapfile.c > > @@ -3518,6 +3518,10 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) > > goto bad_swap_unlock_inode; > > } > > > > + error = init_swap_ops(si); > > + if (error) > > + goto bad_swap_unlock_inode; > > + > > But this part seems wrong? init_swap_ops is called before > setup_swap_extents -> swap_activate sets SWP_FS_OPS, or > SWP_SYNCHRONOUS_IO is set below, so the branches in init_swap_ops > never take effect, am I right? You need to move this someplace after > these flags are set. Maybe right before swapon_mutex so the mutex is a > clean barrier that the swap device will be used and all things before > that will be seen by users, with some comments. Speaking of comments, do you think below sentences are OK to you? diff --git a/mm/swapfile.c b/mm/swapfile.c index 82d2c9b35b11..8012e5e334f9 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -3518,10 +3518,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) goto bad_swap_unlock_inode; } - error = init_swap_ops(si); - if (error) - goto bad_swap_unlock_inode; - si->max = maxpages; si->pages = maxpages - 1; nr_extents = setup_swap_extents(si, swap_file, &span); @@ -3616,6 +3612,15 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) goto free_swap_zswap; } + /* + * init_swap_ops() sets si->ops based on flags. It does not need + * swapon_mutex, and must complete before enable_swap_info() + * exposes the device. + */ + error = init_swap_ops(si); + if (error) + goto bad_swap_unlock_inode; + mutex_lock(&swapon_mutex); prio = DEF_SWAP_PRIO; if (swap_flags & SWAP_FLAG_PREFER)