From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f41.google.com (mail-wm1-f41.google.com [209.85.128.41]) (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 2D07C3F6C4E for ; Tue, 19 May 2026 09:21:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.41 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779182517; cv=none; b=hMiA0o/TmKpcuPB/eX8eQf9j7c6Drhok4PBDV7L6DVMKDnZQE92Ku4GmX1novapbo4VS3x46XcWlPspS5ixHTEuBr4lE7MstVNHv6n/Iybb3sEjwgysIvkv9P2yUVb5912oHvJA9I/+80ev1tmsPJyDYG6l3ks/Bhp7h445zC9U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779182517; c=relaxed/simple; bh=wSz4n6ZHAULGvzhTDNuqX4TTX95Vfl31WZE4J82fus8=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=Cj8g0FFCq7kkWnXtDuvuljq2pU8aFV/jhsvNHyMmQ0XBdQk3DG+/t2DBA3+vhjPEF5cHqM1K+fi+xtONPSGu2mEbl5rK6MulLzL5YP5mbRA8qPRMi7StdxsnXTTgy3yGr7ObLszryH10Pcr2hKEJcW7I7CEp8JeOr46+9lUYsTo= 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=TXpWbKTo; arc=none smtp.client-ip=209.85.128.41 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="TXpWbKTo" Received: by mail-wm1-f41.google.com with SMTP id 5b1f17b1804b1-48896199cbaso26069605e9.1 for ; Tue, 19 May 2026 02:21:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1779182511; x=1779787311; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:from:to:cc:subject:date :message-id:reply-to; bh=QoHvwM4p61ukSgPZjfDBcRJdrzaBcrrvLVu02xCIKiI=; b=TXpWbKTojEsG/x9DQwsk/0H+XskySEyrX0rBufagIM5coaGZbN4GMMyWHMx4wOTKnO 6nM1l2EQGpvGlehe2RC3T4ZBB1WXsj5Rf1E3MrufZxH1mcHQuV2DAjr18FBVYOUqYjgc +6y1OM/nUF90Z8+DA5+FZSGWcJgji8lL/IivBQGcVB2VBugHWaXZs3DvHHfOHbKVJOLc vV+FsJBSqOSx/H3aGa+CQ0UCZvTUjL0to9I1RZpRrMVSq0L1BHC0/CMKYJEwpHBcmjhf OXkr4+d8/+ve/13fJL8u6Pr2sBaon2BIZEsoQmRkPYR4psV5RmARGkuLDY7jOuB2fCFu Dd5Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1779182511; x=1779787311; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=QoHvwM4p61ukSgPZjfDBcRJdrzaBcrrvLVu02xCIKiI=; b=Iok4KRt4OLL4JQPY0aak58MwlUvljacn/k5JZ0UKLDHCaZVSWlF2mwnzgM9oWYt8f2 PXTNyl7vIxkBJabXAO1h1nTKzm4o4HENraEIR9i37H5zH8Yei0eZeLxaqGe+3ihkzg67 Fn2qU6L9haLgcTVsZX+uons3Am1dpWVVb32q1E3lycmnvIkGaB8MFc5u75guNsHLSel1 NUoPAP6Tpesow1TBo6H/bnLePN55yDtmGpQdwRm9MpLqhHI7Ns6rRUmeBWpYqIqJhjan 3pFPtkMWDhypjRYVG9DVzgAyHIBBoHyu2dtoGMQuspBpmrZ21uAilicB7oeRAXQBTQA+ llqQ== X-Forwarded-Encrypted: i=1; AFNElJ9WODlrjVnuXrXJquTJxKpvW+0yWLiSrc0RolPfoCepjueIvoTRTlUo5ZBxHVhaAWjPBOddZvDcaA==@vger.kernel.org X-Gm-Message-State: AOJu0YytKRH3VcvBZd0a5YWC70PQjBY0CZ/dzikM6Z1YNSmfBGae1CWl 04bcphZ9omgWg9ETrQvPHf2SqhYt6r+dR76rLJDFBo+Rv8n/riv+nxkx X-Gm-Gg: Acq92OHkmR9INf+mf8+5BdJibIMp2krlQrPNBjxtT9OdEdq6BmEdtAodJXr5F4bkyat E1d35DNMjDXMp+CZ20mt2xS/9SpJ0tx5LA1NeGAdNoqIiirp3BBcCDuAuirYxzLg0pMGkLWqHDV y7rW33LrFxws5zKYhyUjOC+2KxgTIuazecteSPvbJ1CDri/DwMjMmfFj1qwEFL6+GmNRmwx4Rpg Pvy2Xg1Jg9Xv7uB0+oeB2HpdT3Ha7GtDA1BARo2OWVYwHPXnHreHGahyiGuP2zzPjEDvenLhpwi Pa799TRAHkAyK+7XM628m9XTpPHXIl2SFZ+SDM5NjMTRYndF2OmHHL2L6+AsdLT2Fw93pN+/XlV 8PhnWECaaPW3iElnDFYLkk+Mc4Ny74bPMkDa0dWs5qBup3xBXBEQzuaBRQU+cuYdfp7cPLSgpCb jsgXN/xI/z5+o5rv4a+S5DD0mJ5c7PqHYl8w2tnXNhMgCZgQh9b6sbiJOfPlH7MSeKQIwTZHf5d oM= X-Received: by 2002:a05:600c:4f13:b0:485:30d4:6b9e with SMTP id 5b1f17b1804b1-48fe6328bb7mr321111245e9.21.1779182510799; Tue, 19 May 2026 02:21:50 -0700 (PDT) Received: from pumpkin (82-69-66-36.dsl.in-addr.zen.co.uk. [82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48feab2a23dsm102576065e9.5.2026.05.19.02.21.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 May 2026 02:21:50 -0700 (PDT) Date: Tue, 19 May 2026 10:21:48 +0100 From: David Laight To: Pavel Begunkov Cc: Christoph Hellwig , Jens Axboe , Keith Busch , Sagi Grimberg , Alexander Viro , Christian Brauner , Andrew Morton , Sumit Semwal , Christian =?UTF-8?B?S8O2bmln?= , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, Nitesh Shetty , Kanchan Joshi , Anuj Gupta , Tushar Gohad , William Power , Phil Cayton , Jason Gunthorpe Subject: Re: [PATCH v3 04/10] block: introduce dma map backed bio type Message-ID: <20260519102148.21d42afc@pumpkin> In-Reply-To: <24833f76-2289-4859-86d1-9215b11a1258@gmail.com> References: <646ecd6fde8d9e146cb051efb514deb27ce3883e.1777475843.git.asml.silence@gmail.com> <20260513081929.GD5477@lst.de> <24833f76-2289-4859-86d1-9215b11a1258@gmail.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 18 May 2026 11:29:54 +0100 Pavel Begunkov wrote: > On 5/13/26 09:19, Christoph Hellwig wrote: > >> + if (!bio_flagged(bio_src, BIO_DMABUF_MAP)) { > >> + bio->bi_io_vec = bio_src->bi_io_vec; > >> + } else { > >> + bio->dmabuf_map = bio_src->dmabuf_map; > >> + bio_set_flag(bio, BIO_DMABUF_MAP); > >> + } > > > > This is backwards, please avoid pointless negations: > > I can flip it, but compilers tend to prefer the true branch. E.g. this > > if (cond) A; else B; > C; > > can get compiled into: > > jmpcc cond B > A: ... > C: > return; > B: ... > jmp C; I'm pretty sure gcc completely ignores the order. Some very old compilers didn't - to the extreme of generating a short conditional branch around a long unconditional branch to get past a large 'true' code block. likely() and unlikely() can change things, they are definitely useful comments to a human (or Human) reader. I'm not sure you can rely on the branch predictor to do anything sensible outside of a loop. -- David