Set O_NOATIME flag on Linux #2816
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greatroar
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MichaelEischer
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Dec 30, 2021
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LGTM. I've rebased the PR, moved the setFlags call to fs_local.go (see commit message) and updated to test.
@greatroar Can you have a look at my modifications to the setFlags usages?
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@greatroar Can you have a look at my modifications to your PR? |
Citing Kerrisk, The Linux Programming Interface:
The O_NOATIME flag is intended for use by indexing and backup
programs. Its use can significantly reduce the amount of disk
activity, because repeated disk seeks back and forth across the
disk are not required to read the contents of a file and to update
the last access time in the file’s i-node[.]
restic used to do this, but the functionality was removed along with the
fadvise call in restic#670.
The archiver uses FS.OpenFile, where FS is an instance of the FS interface. This is different from fs.OpenFile, which uses the OpenFile method provided by the fs package.
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Merged the t.Log message into t.Skip setflags_linux_test.go. Your changes LGTM. |
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Thanks for checking. |
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What is the purpose of this change? What does it change?
The O_NOATIME flag is set when opening a file on Linux, which prevents the access time from being updated on every read.
Citing Kerrisk, The Linux Programming Interface:
Was the change discussed in an issue or in the forum before?
restic used to do this, but the functionality was removed along with the fadvise call in #670. That solved #666, which is unrelated to O_NOATIME.
The implementation here is different: it uses fcntl, so we don't need to open the file twice when an error occurs (leading to duplicate path traversals). Errors are expected to be common, as O_NOATIME is only available to the owner of a file or root. Also, fcntl can set O_DIRECT on FreeBSD and is needed to set F_NOCACHE on MacOS, in case we ever want to do that.
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changelog/unreleased/that describes the changes for our users (template here)gofmton the code in all commits