Received: by 2002:a25:2c96:0:0:0:0:0 with SMTP id s144csp426955ybs; Sun, 24 May 2020 09:32:55 -0700 (PDT) X-Google-Smtp-Source: ABdhPJz4lMwm1c/bh6YkvEjTvY5dllycs/YrWuRAqv9GhfoepcctH6ZH+0Ma0H92wO+5Uh852lP3 X-Received: by 2002:a50:f391:: with SMTP id g17mr12233293edm.102.1590337974925; Sun, 24 May 2020 09:32:54 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1590337974; cv=none; d=google.com; s=arc-20160816; b=RbUlHg4QtdQJeSUCss0g4RU12GYdqMdSZJ7SzcwyuLpu01hfpIkQ7SzznlOuBPL2le wveBEFrZu6hBrJ1Fi3U/vo0P/So3DV0UPoGgyP3PnHgtmyEI9oeFbamPgT+A/r0XD4eJ S7pJvXnxoEgA44xyLdwmb8Eqzyf9SREErIuRjQSCCSDLIsdpPeTDakIleWIy0vtWJcfJ YlzoycV4FYfMAE9+ILLDKcCviKinEC1lHPsZLC77om806g9Vv/dlAD3tbNiIePWKjauf No5Fx34j2AKBNkoW6i/xbR3L8UfVPsUW5sxU+KeZ/obXWoM1TNLhWLVHjnmvemGezoaR qVbg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:content-transfer-encoding :content-language:in-reply-to:mime-version:user-agent:date :message-id:from:references:cc:to:subject:dkim-signature; bh=JN/e+A9ktyHXM8zsyrn02aJMxhSbMiH8/CW921mNbJc=; b=fYZ8sL/Z5AK4Ugr/XEgnUZ0kmeSyVF+7355WeKAsdfhdyZp1vMEkwusE8spTuSDyhB RZgQKGMKuOwUjYpF/6vUsbxBHDH7nXvQ0Ubjfjdq+CZFpxpZAl92+Vtf/fpcjdl+t8+0 6CPt9VFFVxVDIq6THPuLb/6HJwpi4r5LEbF7nArBGBcgobQyz7PDfM1mAEVNdN0EPZmV miFSKUQ1ZZrBYzyPRoAz4L7WvW/M1V9fJnSfIB/4Y2VoYKknXPjvPbTAv76yhP++DrLI hgcVcj/25dF8d5C81beYnl3GJrJfPzKGnpkV+5ZP5T4t/nJlTKpQxRcpkavAlPkbQdM8 Ql7w== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@kernel-dk.20150623.gappssmtp.com header.s=20150623 header.b=nmQu6o8G; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Return-Path: Received: from vger.kernel.org (vger.kernel.org. [23.128.96.18]) by mx.google.com with ESMTP id c5si2952096edq.200.2020.05.24.09.32.30; Sun, 24 May 2020 09:32:54 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel-dk.20150623.gappssmtp.com header.s=20150623 header.b=nmQu6o8G; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728316AbgEXQar (ORCPT + 99 others); Sun, 24 May 2020 12:30:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38526 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727899AbgEXQaq (ORCPT ); Sun, 24 May 2020 12:30:46 -0400 Received: from mail-pj1-x1043.google.com (mail-pj1-x1043.google.com [IPv6:2607:f8b0:4864:20::1043]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 69D8FC05BD43 for ; Sun, 24 May 2020 09:30:45 -0700 (PDT) Received: by mail-pj1-x1043.google.com with SMTP id l73so3322449pjb.1 for ; Sun, 24 May 2020 09:30:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=JN/e+A9ktyHXM8zsyrn02aJMxhSbMiH8/CW921mNbJc=; b=nmQu6o8G5J+l4W4zBcQp+jsl3Uw+smSVCJtpS5T4yTJA1GGwd8/BAGRhBqMPopGKIO KWVANpynxh85QYUvlV5rO8XjAPqs//u8yPnD1I5y6NTb8H3mCizC8VVC2x33wBncbGZk +35uSLRNn9+PyaGO4oGDCOrdUiKMq86a2LKXF1k7S24lQwLtyoiZyKxu/olMYC8dpv7D VW9av1A11ah7C3/YFl3fo4X6OZK/UacH6xrxHnj6V0bam5MU/qHdAOqdN2yqgwluSqMy sTvxfgXqVT7aUwQXOND45i9ojAn7Qpk8fDNxaZW5dQym4SPC5SFhMKop7cJ8SrmLYhLu TKOA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=JN/e+A9ktyHXM8zsyrn02aJMxhSbMiH8/CW921mNbJc=; b=f1xtc7ozETwmUM/Z47Lhw42GcJUVVwhCAgWV1panXElxvl8nppvsut9/CX614uMHvN C20+GG8LxFRg+3e8ULHMmdQpbLvusuViWStqFN/AGwvvmzFmMOxpRkFyWdMnDrfLBL7l hR9TtJErQfcXhmcyObInBjErv+ZMPjsH95UIplH+O+vc8GJeeErURnAAZqT9f7cqSTjT RWShmy6hu1VSvTJKgV6VlJQEp93HncyXomcEM6utXSoEUrn1r764Hsdp3MTl7T8vwWoC edbgiAxCZVtjG/pymhyijP6n93S6yJzJNXhsYRY0ighl/p7/o2isatUoJCqpBmZjSIVL SwoA== X-Gm-Message-State: AOAM533+5g2OUugeKgXCu8fdtUgCeDLCdDKeP5HiQK1hUY/7PZi6S4GJ RI/+Coo6SUBA6Tx/OHhILwfXptr0S0SSDw== X-Received: by 2002:a17:90a:890b:: with SMTP id u11mr5692496pjn.233.1590337844549; Sun, 24 May 2020 09:30:44 -0700 (PDT) Received: from ?IPv6:2605:e000:100e:8c61:8568:4ec4:ebd3:32d1? ([2605:e000:100e:8c61:8568:4ec4:ebd3:32d1]) by smtp.gmail.com with ESMTPSA id go1sm10608240pjb.26.2020.05.24.09.30.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 24 May 2020 09:30:43 -0700 (PDT) Subject: Re: [PATCH 05/12] mm: support async buffered reads in generic_file_buffered_read() To: Trond Myklebust , "io-uring@vger.kernel.org" Cc: "linux-mm@kvack.org" , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" References: <20200523185755.8494-1-axboe@kernel.dk> <20200523185755.8494-6-axboe@kernel.dk> <264614fc4fa08df2b0899da1cd38bb07150cd7f3.camel@hammerspace.com> From: Jens Axboe Message-ID: <2fa7104a-ea85-55f2-692c-514eb3b88a88@kernel.dk> Date: Sun, 24 May 2020 10:30:42 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <264614fc4fa08df2b0899da1cd38bb07150cd7f3.camel@hammerspace.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/24/20 8:05 AM, Trond Myklebust wrote: > On Sat, 2020-05-23 at 12:57 -0600, Jens Axboe wrote: >> Use the async page locking infrastructure, if IOCB_WAITQ is set in >> the >> passed in iocb. The caller must expect an -EIOCBQUEUED return value, >> which means that IO is started but not done yet. This is similar to >> how >> O_DIRECT signals the same operation. Once the callback is received by >> the caller for IO completion, the caller must retry the operation. >> >> Signed-off-by: Jens Axboe >> --- >> mm/filemap.c | 33 ++++++++++++++++++++++++++------- >> 1 file changed, 26 insertions(+), 7 deletions(-) >> >> diff --git a/mm/filemap.c b/mm/filemap.c >> index c746541b1d49..a3b86c9acdc8 100644 >> --- a/mm/filemap.c >> +++ b/mm/filemap.c >> @@ -1219,6 +1219,14 @@ static int __wait_on_page_locked_async(struct >> page *page, >> return ret; >> } >> >> +static int wait_on_page_locked_async(struct page *page, >> + struct wait_page_queue *wait) >> +{ >> + if (!PageLocked(page)) >> + return 0; >> + return __wait_on_page_locked_async(compound_head(page), wait, >> false); >> +} >> + >> /** >> * put_and_wait_on_page_locked - Drop a reference and wait for it to >> be unlocked >> * @page: The page to wait for. >> @@ -2058,17 +2066,25 @@ static ssize_t >> generic_file_buffered_read(struct kiocb *iocb, >> index, last_index - index); >> } >> if (!PageUptodate(page)) { >> - if (iocb->ki_flags & IOCB_NOWAIT) { >> - put_page(page); >> - goto would_block; >> - } >> - >> /* >> * See comment in do_read_cache_page on why >> * wait_on_page_locked is used to avoid >> unnecessarily >> * serialisations and why it's safe. >> */ >> - error = wait_on_page_locked_killable(page); >> + if (iocb->ki_flags & IOCB_WAITQ) { >> + if (written) { >> + put_page(page); >> + goto out; >> + } >> + error = wait_on_page_locked_async(page, >> + iocb- >>> private); > > If it is being used in 'generic_file_buffered_read()' as storage for a > wait queue, then it is hard to consider this a 'private' field. private isn't the prettiest, and in fact this one in particular is a bit of a mess. It's not clear if it's caller or callee owned. It's generally not used, outside of the old usb gadget code, iomap O_DIRECT, and ocfs2. With FMODE_BUF_RASYNC, the fs obviously can't set it if it uses ->private for buffered IO. > Perhaps either rename and add type checking, or else add a separate > field altogether to struct kiocb? I'd hate to add a new field and increase the size of the kiocb... One alternative is to do: union { void *private; struct wait_page_queue *ki_waitq; }; and still use IOCB_WAITQ to say that ->ki_waitq is valid. There's also 4 bytes of padding in the kiocb struct. And some fields are only used for O_DIRECT as well, eg ->ki_cookie which is just used for polled O_DIRECT. So we could also do: union { unsigned int ki_cookie; struct wait_page_queue *ki_waitq; }; and still not grow the kiocb. How about we go with this approach, and also add: if (kiocb->ki_flags & IOCB_HIPRI) return -EOPNOTSUPP; to kiocb_wait_page_queue_init() to make sure that this combination isn't valid? -- Jens Axboe