From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ej1-f42.google.com (mail-ej1-f42.google.com [209.85.218.42]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5FB8F20A5CB; Tue, 4 Mar 2025 16:40:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.218.42 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741106435; cv=none; b=kyzMyP1plp3A7c+/6wlu7VbSZhXilASY6mrFqnQyM4rAcGwFAGZC/TFfRBbjYs/5iM4r2i89+mXioVB4Soqjdt/nggRjs5xYkV8cNNa8sGQKqSo6il5zoOEA/4/yVLdY+ZnJtCgKXtVW2Ygb8j+oRNhXKWDA9KKqdUQFaXppLa0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741106435; c=relaxed/simple; bh=2VDiqVcWiJkATlvJCckba4T5+jgOb0RQXaMZPFZlXZI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qXiS7bxcZefgJ5ldgW2TiRl4U2Dy6t/3DBL6HDxepvG3EqfdCM2b76LPjPlIPsiWhgTacdXGOhfnG31DTn+YKALuaMZ0lB7Jmc0XoTJ1f20ONe5nZx7O7zn6B6Irt4u42OIEya08Xbd5rFfYVaZKq/l8yYzdrkjtPXUkMo17tJ0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=fJ6KMhuP; arc=none smtp.client-ip=209.85.218.42 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="fJ6KMhuP" Received: by mail-ej1-f42.google.com with SMTP id a640c23a62f3a-abf5f4e82caso559960366b.1; Tue, 04 Mar 2025 08:40:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1741106431; x=1741711231; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=LSsDnF4kIyj9adBSMmkWoIZqOQRbV5XA37b63dv1tgk=; b=fJ6KMhuPTgGH6InY57GvD+mTP01fZG39tho8k0HZC/Bg2fdsNiCk7SAG7Zoqct7ROU ZRb2r0kyzpTBOmVhqrJKOjbuJf9rc/rADbr+m0HJXr9e3HQoOpmitJGLUP3ZEoi9xZfB 5oG1y/AWSwb8B47IIYy7oRjPV7kB/BLz6/qAPPWIr4ZVOf+1AeFjzvf9Jtvm62P56fRv /XeG4kSL0JXlY+QcCBsGo7SGzI3xsiPb4pfgsz8s7OcLMN0P1HvIPFJ9VujNRppz4zsQ HeRpD5TKhP48iFHgW2NiYKZJGNN5UdNvW82JD5zJ+u2V1meFRlguhBPubsOD1HbWnv9F rohQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1741106431; x=1741711231; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=LSsDnF4kIyj9adBSMmkWoIZqOQRbV5XA37b63dv1tgk=; b=CLuxhLMBlxdYhI3yVWnN3RbjwFh9sAGR7iKazzfNtNI13SazuT6rLp3jw0L37TIWxF bgPVCFI420/rbOg2UFlL9UE8lgjzPwvhyOHWOpwk2RFH3feHfKe+rQ9M3LcGoQh53NJp OGRrGY8hC0CC32QMY1x2AG8fVJjtdqPdu+0qgxFbPkUWsLlHbWDV5StCVxoYR+tZnDlx QpMyq5VcFZ3Z76sEUYp+8owBpS++Z6DpUAbIh6JLIy01O0gIJUxtC3p8RIOIY8Z6PeIr NFj1jG4MkzLejxxe8W4tmrL7qAdBelC2eQ72fLTo1+Fje2JZ16OuB4KTfeAqmEVMV44P Ei6A== X-Forwarded-Encrypted: i=1; AJvYcCVqijgfx8XkXgx5Qjzy+3pvYOsuAKqx6OUDyOVLttmsGHohwl9EKENODkx9e/Y0xZ542sLSHsjRfZTGPmv3kA==@vger.kernel.org, AJvYcCWHr9eDHDJIgJnZLk0qWYQLWMAOuXtWkEJIHuoTG8Nv0ySmWEbTo7RXTHwMvL6m5utK2l13kgKp4yoI@vger.kernel.org, AJvYcCX3UVMS+ATik1U9rlvTLjN4SsMYoE+0ew0sSF8zoa8KR5481FX1Ec3hZARa9/rGJn8iIRTKggE+KA==@vger.kernel.org X-Gm-Message-State: AOJu0YxIS4DjyZoNEU4Kb7aXQmR8T9Xk9vnPmyWooA2vP8uukamQYLGs qbhHQX1Ir8AH6zhmgXYhWHijoGGoGr6jdOzOS+HavJ6kGPbDA6SQ X-Gm-Gg: ASbGnctfxztJMspL2RRIjyyBSm+imEIov21PqV53gcq7jLlAcihEJwyoUBz+4v25G+R tYx0S+nCNabRObIHmO+yEI5JiP0fQQd//C9mfkFYxXM2UM3cCTwhRNYbpZF6GYCmKQzD6GIKEza pnTzWwzyTc+BvFnCvY7KQL08dXSZuoTxb+anxSLjxSV4h4qefMw7VYewIQZ9kVkHg9R2YMHX3DJ qDq2FK8MrkO8c1P553xfloobgxhSXm6JFHr2saSw5VJMgPhxNOGsiC6ty2O2xp61lAS4zv5/xIR E52qAqn5cO1DIcc62Jx8kGDbCZQvt0BvbMfD/ek84Yl/9hAowpQLp9IM7LOf/gVEV1cS1Wg6SZW sNg== X-Google-Smtp-Source: AGHT+IEktvZVcrMLh6ypH/pDXZ8sSYq0tzUgSoxCiTC958uSo6KFBvRojG2eK8//s1waGVxdqzvbhA== X-Received: by 2002:a17:906:c14c:b0:abf:6225:c91d with SMTP id a640c23a62f3a-abf6225d03emr1383476366b.34.1741106431128; Tue, 04 Mar 2025 08:40:31 -0800 (PST) Received: from ?IPV6:2620:10d:c096:325:77fd:1068:74c8:af87? ([2620:10d:c092:600::1:3bd7]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ac1e917b70asm199237566b.151.2025.03.04.08.40.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 04 Mar 2025 08:40:30 -0800 (PST) Message-ID: <83af597f-e599-41d2-a17b-273d6d877dad@gmail.com> Date: Tue, 4 Mar 2025 16:41:40 +0000 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/1] iomap: propagate nowait to block layer To: Christoph Hellwig Cc: Christian Brauner , linux-fsdevel@vger.kernel.org, Dave Chinner , io-uring@vger.kernel.org, "Darrick J . Wong" , linux-xfs@vger.kernel.org, wu lei References: Content-Language: en-US From: Pavel Begunkov In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 3/4/25 16:07, Christoph Hellwig wrote: > On Tue, Mar 04, 2025 at 12:18:07PM +0000, Pavel Begunkov wrote: >> ((dio->flags & IOMAP_DIO_NEED_SYNC) && !use_fua) || >> - ((dio->flags & IOMAP_DIO_WRITE) && pos >= i_size_read(inode))) >> + ((dio->flags & IOMAP_DIO_WRITE) && pos >= i_size_read(inode))) { >> dio->flags &= ~IOMAP_DIO_CALLER_COMP; >> >> + if (!is_sync_kiocb(dio->iocb) && >> + (dio->iocb->ki_flags & IOCB_NOWAIT)) >> + return -EAGAIN; > > Black magic without comments explaining it. I can copy the comment from below if you wish. >> + if (!is_sync_kiocb(dio->iocb) && (dio->iocb->ki_flags & IOCB_NOWAIT)) { >> + /* >> + * This is nonblocking IO, and we might need to allocate >> + * multiple bios. In this case, as we cannot guarantee that >> + * one of the sub bios will not fail getting issued FOR NOWAIT >> + * and as error results are coalesced across all of them, ask >> + * for a retry of this from blocking context. >> + */ >> + if (bio_iov_vecs_to_alloc(dio->submit.iter, BIO_MAX_VECS + 1) > >> + BIO_MAX_VECS) > > This is not very accurate in times of multi-page bvecs and large order > folios all over. bio_iov_vecs_to_alloc() can overestimate, i.e. the check might return -EAGAIN in more cases than required but not the other way around, that should be enough for a fix such as this patch. Or did I maybe misunderstood you? > I think you really need to byte the bullet and support for early returns > from the non-blocking bio submission path. Assuming you're suggesting to implement that, I can't say I'm excited by the idea of reworking a non trivial chunk of block layer to fix a problem and then porting it up to some 5.x, especially since it was already attempted before by someone and ultimately got reverted. -- Pavel Begunkov