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Tracing syscalls, opening and reading an `xl.meta` looks like this:
```
openat(AT_FDCWD, "/mnt/drive1/ss8-old/testbucket/ObjSize4MiBThreads72/(554O51H/peTb(0iztdbTKw59.csv/xl.meta", O_RDONLY|O_NOATIME|O_CLOEXEC) = 34 <0.000>
fcntl(34, F_GETFL) = 0x48000 (flags O_RDONLY|O_LARGEFILE|O_NOATIME) <0.000>
fcntl(34, F_SETFL, O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_NOATIME) = 0 <0.000>
epoll_ctl(4, EPOLL_CTL_ADD, 34, {events=EPOLLIN|EPOLLOUT|EPOLLRDHUP|EPOLLET, data={u32=3172471557, u64=8145488475984499461}}) = -1 EPERM (Operation not permitted) <0.000>
fcntl(34, F_GETFL) = 0x48800 (flags O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_NOATIME) <0.000>
fcntl(34, F_SETFL, O_RDONLY|O_LARGEFILE|O_NOATIME) = 0 <0.000>
fstat(34, {st_mode=S_IFREG|0644, st_size=354, ...}) = 0 <0.000>
read(34, "XL2 \1\0\3\0\306\0\0\1P\2\2\1\304$\225\304\20\0\0\0\0\0\0\0\0\0\0\0"..., 354) = 354 <0.000>
close(34) = 0 <0.000>
```
Everything until `fstat` is the `os.Open` call.
Looking at the code: https://github.com/golang/go/blob/master/src/os/file_unix.go#L212-L243
It seems for every file it "tries" to see if it is pollable. This causes `syscall.SetNonblock(fd, true)` to be called. This is the first `F_SETFL`.
It then calls `f.pfd.Init("file", true)`. This will attempt to set it as pollable using `epoll_ctl`. This will always fail for files. It therefore calls `syscall.SetNonblock(fd, false)` resulting in the second `F_SETFL`.
If we set the `O_NONBLOCK` call on the initial open, we should avoid the 4 `fcntl` syscalls per file.
I don't see any way to avoid the `epoll_ctl` call, since kind is either `kindOpenFile` or `kindNonBlock`, so "pollable" will always be true. However avoiding 4 of 6 syscalls still seems worth it.
This should not have any effect, since files will end up with "nonblock" anyway.
35 lines
1.1 KiB
Go
35 lines
1.1 KiB
Go
//go:build unix && !darwin && !freebsd
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// Copyright (c) 2015-2021 MinIO, Inc.
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//
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// This file is part of MinIO Object Storage stack
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Affero General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Affero General Public License for more details.
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//
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// You should have received a copy of the GNU Affero General Public License
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// along with this program. If not, see <http://www.gnu.org/licenses/>.
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package cmd
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import (
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"os"
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"syscall"
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)
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var (
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// Disallow updating access times
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// Add non-block to avoid syscall to attempt to set epoll on files.
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readMode = os.O_RDONLY | 0x40000 | syscall.O_NONBLOCK // O_NOATIME
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// Write with data sync only used only for `xl.meta` writes
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writeMode = 0x1000 | syscall.O_NONBLOCK // O_DSYNC
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)
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