From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.burntcomma.com (mail2.burntcomma.com [217.169.27.34]) (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 EEC1E17B505 for ; Thu, 21 Aug 2025 09:20:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.169.27.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755768052; cv=none; b=dg8Y3fUDCxCOjoIsmWeNHrJAcYQKwcy9s5+mbkW2ag/MS+ofXwH1YApf2m/RMci7JCwS9CWLC0V7oTq6kenmDKLiBOZresbKUmc8I1zKUopWlSDmPIG9uWsNe+wG+SmqyZGldb3gzeiON7w+OwpUoRqR0acCp17n5A+y69uihTQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755768052; c=relaxed/simple; bh=d74dX8AxeL9sG6nHN0Ek/gQdyamu62+xnbY/W/YbXIM=; h=Message-ID:Date:Mime-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=UO8fGNk5p7iFBbThzfeNrzrWg0ll0JoageA6plxN9HXWO0uJmu2M36ooldhMAUilpTHrRgkJOo7grfqSuYz1pf7PNYYTlcm7raZzRMTW4zTfU4ij4WXlPNemWl7sVseIqWbJjhndp/Nj/I6Pd1+1vxRyA9udNzvyPhqmh5s1iDs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=harmstone.com; spf=pass smtp.mailfrom=harmstone.com; dkim=pass (1024-bit key) header.d=harmstone.com header.i=@harmstone.com header.b=fW/m/4RP; arc=none smtp.client-ip=217.169.27.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=harmstone.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=harmstone.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=harmstone.com header.i=@harmstone.com header.b="fW/m/4RP" Received: from [IPV6:2a02:8012:8cf0:0:ce28:aaff:fe0d:6db2] (beren.burntcomma.com [IPv6:2a02:8012:8cf0:0:ce28:aaff:fe0d:6db2]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256 client-signature RSA-PSS (2048 bits) client-digest SHA256) (Client CN "hellas", Issuer "burntcomma.com" (verified OK)) by mail.burntcomma.com (Postfix) with ESMTPS id DFEE72AB178; Thu, 21 Aug 2025 10:20:42 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=harmstone.com; s=mail; t=1755768042; bh=j+Q1YLAmxfZuYWh859aSIsCdKqD27eN9x/aH7uCHbpA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=fW/m/4RP3qCaGyVyHPL7xBGCbqRiVYhqdUDPgjtJ1bbrbsYX1q45EhXkpM4lRRUOP cHSXcEHW8R4pJd38dm43lnzs8tFZcIl31L6db+nQ+A9Z9HsS9ifX46DnINaqOKmEFO 1oMlW+eMgvNbPVG7RpjK0l6yJMxpH0+sJCzxz9BY= Message-ID: <32f15414-0ed0-447d-88e0-6368f29a989a@harmstone.com> Date: Thu, 21 Aug 2025 10:20:42 +0100 Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Subject: Re: Newbie questions about DIR_ITEM and DIR_INDEX design To: Sun YangKai Cc: linux-btrfs References: <12726025.O9o76ZdvQC@saltykitkat> <12736164.O9o76ZdvQC@saltykitkat> Content-Language: en-US From: Mark Harmstone Autocrypt: addr=mark@harmstone.com; keydata= xsBNBFp/GMsBCACtFsuHZqHWpHtHuFkNZhMpiZMChyou4X8Ueur3XyF8KM2j6TKkZ5M/72qT EycEM0iU1TYVN/Rb39gBGtRclLFVY1bx4i+aUCzh/4naRxqHgzM2SeeLWHD0qva0gIwjvoRs FP333bWrFKPh5xUmmSXBtBCVqrW+LYX4404tDKUf5wUQ9bQd2ItFRM2mU/l6TUHVY2iMql6I s94Bz5/Zh4BVvs64CbgdyYyQuI4r2tk/Z9Z8M4IjEzQsjSOfArEmb4nj27R3GOauZTO2aKlM 8821rvBjcsMk6iE/NV4SPsfCZ1jvL2UC3CnWYshsGGnfd8m2v0aLFSHZlNd+vedQOTgnABEB AAHNI01hcmsgSGFybXN0b25lIDxtYXJrQGhhcm1zdG9uZS5jb20+wsCRBBMBCAA7AhsvBQsJ CAcCBhUICQoLAgQWAgMBAh4BAheAFiEEG2JgKYgV0WRwIJAqbKyhHeAWK+0FAmRQOkICGQEA CgkQbKyhHeAWK+22wgf/dBOJ0pHdkDi5fNmWynlxteBsy3VCo0qC25DQzGItL1vEY95EV4uX re3+6eVRBy9gCKHBdFWk/rtLWKceWVZ86XfTMHgy+ZnIUkrD3XZa3oIV6+bzHgQ15rXXckiE A5N+6JeY/7hAQpSh/nOqqkNMmRkHAZ1ZA/8KzQITe1AEULOn+DphERBFD5S/EURvC8jJ5hEr lQj8Tt5BvA57sLNBmQCE19+IGFmq36EWRCRJuH0RU05p/MXPTZB78UN/oGT69UAIJAEzUzVe sN3jiXuUWBDvZz701dubdq3dEdwyrCiP+dmlvQcxVQqbGnqrVARsGCyhueRLnN7SCY1s5OHK ls7ATQRafxjLAQgAvkcSlqYuzsqLwPzuzoMzIiAwfvEW3AnZxmZn9bQ+ashB9WnkAy2FZCiI /BPwiiUjqgloaVS2dIrVFAYbynqSbjqhki+uwMliz7/jEporTDmxx7VGzdbcKSCe6rkE/72o 6t7KG0r55cmWnkdOWQ965aRnRAFY7Zzd+WLqlzeoseYsNj36RMaqNR7aL7x+kDWnwbw+jgiX tgNBcnKtqmJc04z/sQTa+sUX53syht1Iv4wkATN1W+ZvQySxHNXK1r4NkcDA9ZyFA3NeeIE6 ejiO7RyC0llKXk78t0VQPdGS6HspVhYGJJt21c5vwSzIeZaneKULaxXGwzgYFTroHD9n+QAR AQABwsGsBBgBCAAgFiEEG2JgKYgV0WRwIJAqbKyhHeAWK+0FAlp/GMsCGy4BQAkQbKyhHeAW K+3AdCAEGQEIAB0WIQR6bEAu0hwk2Q9ibSlt5UHXRQtUiwUCWn8YywAKCRBt5UHXRQtUiwdE B/9OpyjmrshY40kwpmPwUfode2Azufd3QRdthnNPAY8Tv9erwsMS3sMh+M9EP+iYJh+AIRO7 fDN/u0AWIqZhHFzCndqZp8JRYULnspXSKPmVSVRIagylKew406XcAVFpEjloUtDhziBN7ykk srAMoLASaBHZpAfp8UAGDrr8Fx1on46rDxsWbh1K1h4LEmkkVooDELjsbN9jvxr8ym8Bkt54 FcpypTOd8jkt/lJRvnKXoL3rZ83HFiUFtp/ZkveZKi53ANUaqy5/U5v0Q0Ppz9ujcRA9I/V3 B66DKMg1UjiigJG6espeIPjXjw0n9BCa9jqGICyJTIZhnbEs1yEpsM87eUIH/0UFLv0b8IZe pL/3QfiFoYSqMEAwCVDFkCt4uUVFZczKTDXTFkwm7zflvRHdy5QyVFDWMyGnTN+Bq48Gwn1M uRT/Sg37LIjAUmKRJPDkVr/DQDbyL6rTvNbA3hTBu392v0CXFsvpgRNYaT8oz7DDBUUWj2Ny 6bZCBtwr/O+CwVVqWRzKDQgVo4t1xk2ts1F0R1uHHLsX7mIgfXBYdo/y4UgFBAJH5NYUcBR+ QQcOgUUZeF2MC9i0oUaHJOIuuN2q+m9eMpnJdxVKAUQcZxDDvNjZwZh+ejsgG4Ejd2XR/T0y XFoR/dLFIhf2zxRylN1xq27M9P2t1xfQFocuYToPsVk= In-Reply-To: <12736164.O9o76ZdvQC@saltykitkat> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 21/08/2025 9.26 am, Sun YangKai wrote: > Hi Mark, > > Thank you so much for your incredibly helpful, detailed, and patient response. > It’s greatly appreciated and has significantly improved my understanding of > btrfs design choices. > > Best regards, > Sun YangKai No worries. It looks like another factor was the fact that the original version of getdents() returned a 32-bit d_off on 32-bit systems - which is okay for a monotonic counter within a directory, but no good if you want to avoid the birthday paradox. So if you were designing Btrfs from scratch today, you might choose just to have DIR_ITEM, change its hash length to 64 bits, and disallow hash collisions completely. Mark