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[2403:580d:fda1::299]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-6340a449f4csm3566039a12.4.2024.05.10.15.27.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 10 May 2024 15:27:03 -0700 (PDT) Message-ID: Date: Sat, 11 May 2024 07:56:57 +0930 Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 03/11] btrfs: introduce new members for extent_map To: Filipe Manana , Qu Wenruo Cc: linux-btrfs@vger.kernel.org, David Sterba References: <1fe28d75-a4a3-4304-9998-a88a5fee4919@gmx.com> Content-Language: en-US From: Qu Wenruo Autocrypt: addr=wqu@suse.com; keydata= xsBNBFnVga8BCACyhFP3ExcTIuB73jDIBA/vSoYcTyysFQzPvez64TUSCv1SgXEByR7fju3o 8RfaWuHCnkkea5luuTZMqfgTXrun2dqNVYDNOV6RIVrc4YuG20yhC1epnV55fJCThqij0MRL 1NxPKXIlEdHvN0Kov3CtWA+R1iNN0RCeVun7rmOrrjBK573aWC5sgP7YsBOLK79H3tmUtz6b 9Imuj0ZyEsa76Xg9PX9Hn2myKj1hfWGS+5og9Va4hrwQC8ipjXik6NKR5GDV+hOZkktU81G5 gkQtGB9jOAYRs86QG/b7PtIlbd3+pppT0gaS+wvwMs8cuNG+Pu6KO1oC4jgdseFLu7NpABEB AAHNGFF1IFdlbnJ1byA8d3F1QHN1c2UuY29tPsLAlAQTAQgAPgIbAwULCQgHAgYVCAkKCwIE FgIDAQIeAQIXgBYhBC3fcuWlpVuonapC4cI9kfOhJf6oBQJjTSJVBQkNOgemAAoJEMI9kfOh Jf6oapEH/3r/xcalNXMvyRODoprkDraOPbCnULLPNwwp4wLP0/nKXvAlhvRbDpyx1+Ht/3gW p+Klw+S9zBQemxu+6v5nX8zny8l7Q6nAM5InkLaD7U5OLRgJ0O1MNr/UTODIEVx3uzD2X6MR ECMigQxu9c3XKSELXVjTJYgRrEo8o2qb7xoInk4mlleji2rRrqBh1rS0pEexImWphJi+Xgp3 dxRGHsNGEbJ5+9yK9Nc5r67EYG4bwm+06yVT8aQS58ZI22C/UeJpPwcsYrdABcisd7dddj4Q RhWiO4Iy5MTGUD7PdfIkQ40iRcQzVEL1BeidP8v8C4LVGmk4vD1wF6xTjQRKfXHOwE0EWdWB rwEIAKpT62HgSzL9zwGe+WIUCMB+nOEjXAfvoUPUwk+YCEDcOdfkkM5FyBoJs8TCEuPXGXBO Cl5P5B8OYYnkHkGWutAVlUTV8KESOIm/KJIA7jJA+Ss9VhMjtePfgWexw+P8itFRSRrrwyUf E+0WcAevblUi45LjWWZgpg3A80tHP0iToOZ5MbdYk7YFBE29cDSleskfV80ZKxFv6koQocq0 vXzTfHvXNDELAuH7Ms/WJcdUzmPyBf3Oq6mKBBH8J6XZc9LjjNZwNbyvsHSrV5bgmu/THX2n g/3be+iqf6OggCiy3I1NSMJ5KtR0q2H2Nx2Vqb1fYPOID8McMV9Ll6rh8S8AEQEAAcLAfAQY AQgAJgIbDBYhBC3fcuWlpVuonapC4cI9kfOhJf6oBQJjTSJuBQkNOge/AAoJEMI9kfOhJf6o rq8H/3LJmWxL6KO2y/BgOMYDZaFWE3TtdrlIEG8YIDJzIYbNIyQ4lw61RR+0P4APKstsu5VJ 9E3WR7vfxSiOmHCRIWPi32xwbkD5TwaA5m2uVg6xjb5wbdHm+OhdSBcw/fsg19aHQpsmh1/Q bjzGi56yfTxxt9R2WmFIxe6MIDzLlNw3JG42/ark2LOXywqFRnOHgFqxygoMKEG7OcGy5wJM AavA+Abj+6XoedYTwOKkwq+RX2hvXElLZbhYlE+npB1WsFYn1wJ22lHoZsuJCLba5lehI+// ShSsZT5Tlfgi92e9P7y+I/OzMvnBezAll+p/Ly2YczznKM5tV0gboCWeusM= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2024/5/10 20:56, Filipe Manana 写道: [...] >> >> Check case 1). >> >> Both file extents are referring to the same data extent. >> >> Like this: >> >> FE 1, file pos 0, num_bytes 4K, disk_bytenr X, disk_num_bytes 16K, >> offset 0, ram_bytes 16K, compression none >> >> FE 2, file pos 4k, num_bytes 4K, disk_bytenr X, disk_num_bytes 16K, >> offset 4k, ram_bytes 16K, compression none. >> >> In that case we should not just sum up the disk_num_bytes at all. >> Remember disk_num_bytes are for the data extent. > > Yes, but for cases where they refer to different file extent items > that are contiguous on disk, the max is confusing, and a sum is what > makes sense. Example: > > FE 1, file pos 0, num_bytes 4K, disk_bytenr X, disk_num_bytes 4K, > offset 0, ram_bytes 4K, no compression > > FE 2, file pos 4K, num_bytes 4K, disk_bytenr X + 4K, disk_num_bytes > 4K, offset 0, ram_bytes 4K, no compression > > When merging the corresponding extent maps it's natural to think > disk_num_bytes is 8K and not 4K. The max based solution is based on their end bytenr, not disk_num_bytes. So the merged one would have: disk_bytenr = min(X, X + 4K) = X disk_num_bytes = max(X + 4K, X + 4K + 4K) - disk_bytenr = 8K. So I didn't see why it's not natural. Furthermore, the max/min based solution can handle both case 1) (same data extent, different parts) and case 2) (different data extents) well. > > But as I mentioned before, after merging we really don't use > disk_num_bytes anywhere. > It's only used during extent logging, which only happens for extents > maps that were not merged and can not be before they are logged. > > Before this patchset, when disk_num_bytes was named orig_block_len, > that was never updated during merging, exactly because we don't use > cases for it. But since we want everything to match the definition of the same-named member, no matter if they get merged or not, we need to change the values. If they do not get used, that's still fine. Thanks, Qu