From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-132.freemail.mail.aliyun.com (out30-132.freemail.mail.aliyun.com [115.124.30.132]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 52A0E558BC for ; Mon, 28 Oct 2024 02:28:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.132 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730082503; cv=none; b=sg+HYiVlF33uuWfjR+vFxLTxGIqhCPfyqLhywLcDe3GrmXVPogy2cHF2y5/vM2s25AqAxONyGaavCqwi4e0HRLa6AXi1d4zc2N4bytEy3YOmjFGgfHu+Uqy3wK+aW420S/PKyUJdt+KNprmODltrDSItjPXRxkC/VTw4Au/mVlA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730082503; c=relaxed/simple; bh=sM0wPb+VcYyUVNqH+zKZp7Cgc/ws+aHQp54KfoTL74E=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=DjU8qFhFlg81ndjZDVHfS5o0wgS0xM6WbQ5gtRdCpufqOtte+/Nj4M0o50MRO9W3I/1xzTDt4mZ98oTYmAQ5u/qwVJFTGwLU5def1zRHC2DXzjEk0jfcF1bKJETps9WmsOR7wxOWe/IhkP9VKLp4tODhMk2ub9L6DjDPdKYFOSw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=TWJSFPj2; arc=none smtp.client-ip=115.124.30.132 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="TWJSFPj2" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1730082490; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=VFQl1w/gX77WPMQusxQCra6sXMLdIY9lsYhIe+TixHg=; b=TWJSFPj2tPxzNjh2MEzT54pMzMxTHSH5BAsvH4mIva+bVxuig6V3sWnuvLDkG/fG1TEZWb0lgW6unekxQxz3QorBE6QYEHj4rERKnL2Kjofpl1aNwW0j5igQMfuRdwbbIkb5493JMaub6WyNAd431vrYOJvPMGY0y2lPLTvIM54= Received: from 30.221.148.132(mailfrom:jefflexu@linux.alibaba.com fp:SMTPD_---0WHz.MBB_1730082488 cluster:ay36) by smtp.aliyun-inc.com; Mon, 28 Oct 2024 10:28:09 +0800 Message-ID: <5825a89f-7994-4de5-aecb-ebb6e3f94488@linux.alibaba.com> Date: Mon, 28 Oct 2024 10:28:07 +0800 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/2] fuse: remove tmp folio for writebacks and internal rb tree To: Joanne Koong Cc: Miklos Szeredi , Shakeel Butt , linux-fsdevel@vger.kernel.org, josef@toxicpanda.com, bernd.schubert@fastmail.fm, hannes@cmpxchg.org, linux-mm@kvack.org, kernel-team@meta.com References: <20241014182228.1941246-1-joannelkoong@gmail.com> <3e4ff496-f2ed-42ef-9f1a-405f32aa1c8c@linux.alibaba.com> Content-Language: en-US From: Jingbo Xu In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 10/26/24 2:47 AM, Joanne Koong wrote: > On Fri, Oct 25, 2024 at 10:36 AM Joanne Koong wrote: >> >> On Thu, Oct 24, 2024 at 6:38 PM Jingbo Xu wrote: >>> >>> >>> >>> On 10/25/24 12:54 AM, Joanne Koong wrote: >>>> On Mon, Oct 21, 2024 at 2:05 PM Joanne Koong wrote: >>>>> >>>>> On Mon, Oct 21, 2024 at 3:15 AM Miklos Szeredi wrote: >>>>>> >>>>>> On Fri, 18 Oct 2024 at 07:31, Shakeel Butt wrote: >>>>>> >>>>>>> I feel like this is too much restrictive and I am still not sure why >>>>>>> blocking on fuse folios served by non-privileges fuse server is worse >>>>>>> than blocking on folios served from the network. >>>>>> >>>>>> Might be. But historically fuse had this behavior and I'd be very >>>>>> reluctant to change that unconditionally. >>>>>> >>>>>> With a systemwide maximal timeout for fuse requests it might make >>>>>> sense to allow sync(2), etc. to wait for fuse writeback. >>>>>> >>>>>> Without a timeout allowing fuse servers to block sync(2) indefinitely >>>>>> seems rather risky. >>>>> >>>>> Could we skip waiting on writeback in sync(2) if it's a fuse folio? >>>>> That seems in line with the sync(2) documentation Jingbo referenced >>>>> earlier where it states "The writing, although scheduled, is not >>>>> necessarily complete upon return from sync()." >>>>> https://pubs.opengroup.org/onlinepubs/9699919799/functions/sync.html >>>>> >>>> >>>> So I think the answer to this is "no" for Linux. What the Linux man >>>> page for sync(2) says: >>>> >>>> "According to the standard specification (e.g., POSIX.1-2001), sync() >>>> schedules the writes, but may return before the actual writing is >>>> done. However Linux waits for I/O completions, and thus sync() or >>>> syncfs() provide the same guarantees as fsync() called on every file >>>> in the system or filesystem respectively." [1] >>> >>> Actually as for FUSE, IIUC the writeback is not guaranteed to be >>> completed when sync(2) returns since the temp page mechanism. When >>> sync(2) returns, PG_writeback is indeed cleared for all original pages >>> (in the address_space), while the real writeback work (initiated from >>> temp page) may be still in progress. >>> >> >> That's a great point. It seems like we can just skip waiting on >> writeback to finish for fuse folios in sync(2) altogether then. I'll >> look into what's the best way to do this. > > I think the most straightforward way to do this for sync(2) is to add > the mapping check inside sync_bdevs(). With something like: > > diff --git a/block/bdev.c b/block/bdev.c > index 738e3c8457e7..bcb2b6d3db94 100644 > --- a/block/bdev.c > +++ b/block/bdev.c > @@ -1247,7 +1247,7 @@ void sync_bdevs(bool wait) > mutex_lock(&bdev->bd_disk->open_mutex); > if (!atomic_read(&bdev->bd_openers)) { > ; /* skip */ > - } else if (wait) { > + } else if (wait && > !mapping_no_writeback_wait(inode->i_mapping)) { > /* > * We keep the error status of individual mapping so > * that applications can catch the writeback error using > > I'm afraid we are waiting in wait_sb_inodes (ksys_sync -> sync_inodes_sb -> wait_sb_inodes) rather than sync_bdevs. sync_bdevs() is used to writeback and sync the metadata residing on the block device directly such as the superblock. It is sync_inodes_one_sb() that actually writeback inodes. -- Thanks, Jingbo