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[70.77.221.9]) by smtp.gmail.com with ESMTPSA id x52-20020a056a000bf400b00592591d1634sm1597492pfu.97.2023.02.16.09.08.03 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 16 Feb 2023 09:08:04 -0800 (PST) From: Andreas Dilger Message-Id: <542D3378-3214-4D0D-AA63-5A149E2B00EE@dilger.ca> Content-Type: multipart/signed; boundary="Apple-Mail=_2AA5044B-1570-4816-8AA0-ED824D970CD1"; protocol="application/pgp-signature"; micalg=pgp-sha256 Mime-Version: 1.0 (Mac OS X Mail 10.3 \(3273\)) Subject: Re: [PATCH v3 7/8] ext4: Use rbtrees to manage PAs instead of inode i_prealloc_list Date: Thu, 16 Feb 2023 10:07:39 -0700 In-Reply-To: <20230210143753.ofh6wouk7vi7ygcl@quack3> Cc: Ojaswin Mujoo , Ext4 Developers List , Theodore Ts'o , Ritesh Harjani , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, rookxu , Ritesh Harjani To: Jan Kara References: <20230116080216.249195-8-ojaswin@linux.ibm.com> <20230116122334.k2hlom22o2hlek3m@quack3> <20230117110335.7dtlq4catefgjrm3@quack3> <20230127144312.3m3hmcufcvxxp6f4@quack3> <20230209105418.ucowiqnnptbpwone@quack3> <20230210143753.ofh6wouk7vi7ygcl@quack3> X-Mailer: Apple Mail (2.3273) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --Apple-Mail=_2AA5044B-1570-4816-8AA0-ED824D970CD1 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=us-ascii On Feb 10, 2023, at 7:37 AM, Jan Kara wrote: > So I belive mballoc tries to align everything (offsets & lengths) > to powers of two to reduce fragmentation and simplify the work for > the buddy allocator. If ac->ac_b_ex.fe_len is a power-of-two, the > alignment makes sense. But once we had to resort to higher allocator > passes and just got some random-length extent, the alignment stops > making sense. In addition to optimizing for the buddy allocator, the other reason that the allocations are aligned to power-of-two offsets is to better align with underlying RAID stripes. Otherwise, unaligned writes will cause parity read-modify-write updates to multiple RAID stripes. This alignment can also help (though to a lesser degree) with NAND flash erase blocks. Cheers, Andreas --Apple-Mail=_2AA5044B-1570-4816-8AA0-ED824D970CD1 Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc Content-Description: Message signed with OpenPGP -----BEGIN PGP SIGNATURE----- Comment: GPGTools - http://gpgtools.org iQIzBAEBCAAdFiEEDb73u6ZejP5ZMprvcqXauRfMH+AFAmPuYtsACgkQcqXauRfM H+Cu9g//YCZ+jwypTgq+CU4GrHRWfQgwIIsAagt/+hIQ49+p2psufXRuWBYuVvXo JhbGVzk6yztNm81QBZp1unYEnm5Gkkeq7AD1J19zE3v2muHTU413Xf5UFTP7ZzLt 6s84jHucEbPITzX+YkxxbAMF819KdgN7UDMnJ9K5mC1bvJtFOE5TWkMXCZSZEyhb Njg2UWRZ1L+JfFejIPmiDStL89Ae4ryhatVYg5LLEGmXMNx1Su/n2Vd8mqzq6KnF Ek0Z8Hz1XI0GGNugZiG+LziCzGXsE53in34LXUwXd7ZnU/OIZ0B/GF6q8SbKW2C5 VdrED+FifNFXsxhUCxDhfl5wEO8TASMPaUuF6qbNXsXF3cSPb3qb+ec5e+0EycjC TpGGPHDo2Ik3/wLtGJ/oTl9sdv8SPDxlStfL4+oL6jmcGOoF2Ihh9Hg80UnQHLnR 9dWU6PYcR8KKBaqJH9euWzLr6cTx8MxBzZDDUCJxT6UWpK+WjBebLazSarvVqS4h yxAGZDaKtF3CjYkb24nrrz7yUDTO7uaj93NJO5ADwg4KszHAVxBSUStxKgCyUR/Y bEigne4D7B7TaH4l2kPckhfwwCpxnhqmCoYqAyWqKHRySkXxFVcjw4/ApLQ+/KPX 2UlaN5gf6z8PUSkp0mXLCWBFDsXvJTFqF1gy7Fv2YfCHaaMBKaI= =C/5g -----END PGP SIGNATURE----- --Apple-Mail=_2AA5044B-1570-4816-8AA0-ED824D970CD1--