From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 BBD75221721; Wed, 28 May 2025 22:22:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748470947; cv=none; b=LlonZiusZ5PyW7XlM7Qmf/g/9QS0wBhm0JUfpIbPgbQYbHp3AzY7xK7Zs00LO7sFXNF8ZFoqM2MKXgXZURpDIXUUwHWE1FABQkSf/xnObYEc1AtTnq6EJmizRD3MGzuo3dfGzLwm4KSwQAq1N+N5B+QYeJ7oMZkEAIKTSZrZFzI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748470947; c=relaxed/simple; bh=eqIsvYmimSK/DqV2hNI3lKHjY6it5CNEBd71JQNxKOQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=mBThSANhbgElphKx/mkqp7OV1Rkc8+q/hYM04FLYOrgsi48hATAcc3Gu3Ez5BYfSLp/GSHTGlDaRp4JiXIuSId1+CZ9e6ISqU4uZx+E4miN23sac34I5XwIihkRav5wnlyW6N0QL0/vrZdBZ+6O+eWQQcHJG+t1DEMcrYg4ASPA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=EuVzzytT; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="EuVzzytT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 181CEC4CEE3; Wed, 28 May 2025 22:22:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1748470947; bh=eqIsvYmimSK/DqV2hNI3lKHjY6it5CNEBd71JQNxKOQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=EuVzzytTowoEFY87+SEomMrGrm526KbP5P9QCWJ/qB2j1dgmSd11y2hb4LmtybOLg QPU3CrLr63BIKWkADEXkVdLrITmiiTCNQ+sFdzlPev0+5f+2rkbUjzuDCSaIJu8MRh HuqRMQzg/5Gm7icNLROIxFNUWt6dq1uypCGbzUJJcmNab7UEagpvojMJy2Oz7ZQp6s Zq3RFGsHJEDbsySr+adwIBMAWs6zILimcb1QbCOHKAD96MT6coqmr68Nmr7OeEpPJ4 y5gQOW3Nxd5+GR1mpbysY7MPkQwpYP7TECM1tYYwoainwQj2d1tDAot7aAXSFPIE5Q q2HGzxnMJUvjw== Date: Wed, 28 May 2025 15:22:26 -0700 From: "Darrick J. Wong" To: Christoph Hellwig Cc: zlang@redhat.com, fstests@vger.kernel.org, linux-xfs@vger.kernel.org Subject: Re: [PATCH 3/4] xfs/259: try to force loop device block size Message-ID: <20250528222226.GB8303@frogsfrogsfrogs> References: <174786719374.1398726.14706438540221180099.stgit@frogsfrogsfrogs> <174786719445.1398726.2165923649877733743.stgit@frogsfrogsfrogs> Precedence: bulk X-Mailing-List: fstests@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, May 22, 2025 at 10:19:00PM -0700, Christoph Hellwig wrote: > On Wed, May 21, 2025 at 03:41:36PM -0700, Darrick J. Wong wrote: > > From: Darrick J. Wong > > > > Starting with 6.15-rc1, loop devices created with directio mode enabled > > will set their logical block size to whatever STATX_DIO_ALIGN on the > > host filesystem reports. If you happen to be running a kernel that > > always sets up loop devices in directio mode > > Such a kernel has some weird out of tree patches. Why would we want > to support that? Welll... the only reason I patched the loop driver to turn ovn directio by default is because writeback throttling for loop devices keeps getting turned on and off randomly. At this point I have NFI if throttling is actually the desired behavior or not. It makes fstests crawl really slowly. On one hand it seems bogus that a loopbacked filesystem with enough dirty pages to trip the thresholds then gets throttled doing writeback to the pagecache of the loop file, but OTOH it /is/ more dirty pagecache. Ultimately I think non-directio loop devices are stupid especially when there are filesystems on top of them, but I bet there's some user that would break if we suddenly started requiring directio alignments. Maybe RWF_DONTCACHE will solve this whenever it stabilizes. --D