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博客旗舰店RFT:"ubd=mmap "实验性配置选项

RFT:"ubd=mmap "实验性配置选项

要求测试!

如果你们中的一些人能够测试一个新的选项,改变 UML 写入文件系统文件的方式,并在这里发表你们的经验,我将非常感激。

通常,UML使用标准的打开/关闭读/写库调用。 这样做的问题是,它在主机的页面缓存中重复了数据,并影响了所有磁盘i/o的性能。 新选项将文件系统文件直接映射到页面缓存中,所以它消除了页面的重复拷贝和页面缓存的浪费。

你会注意到在 "编辑配置文件 "页面有一个新的 "实验性选项"。 要打开它,启用ubd=mmap,保存并重新启动。 你应该在内核选项下的dmesg中注意到它。(dmesg | grep mmap)

一旦我们有了一堆成功的报告,我就会考虑为大家启用这个功能。

[color=darkred][b]警告:[/b][/color][/size] 我不建议任何人打开这个功能。 像这样一个成熟的功能,总是有可能出现数据丢失。 Jeff Dike在上个月修复了ubd=mmap的最后一个已知错误,它吃掉了超过4GB的文件系统(所以这将是一个很好的测试),所以要谨慎使用这个选项。 在 UML 邮件列表中还没有任何与 mmap 有关的故障报告,但这不是一个广为人知的选项。

目前的版本(在2.4.24内核中)在启用mmap的情况下对我来说运行良好,但你的里程可能有所不同。

谢谢、
-克里斯


评论 (7)

  1. Author Photo

    I’m game. 🙂

    I just rebooted my linode with it enabled. I do nightly backups, so I am not overly concerned. Here’s hoping for the best..

  2. Author Photo

    That went badly.

    From dmesg:

    EXT3-fs error (device ubd(98,32)) in ext3_reserve_inode_write: IO failure
    EXT3-fs error (device ubd(98,32)) in ext3_orphan_add: IO failure
    attempt to access beyond end of device
    62:20: rw=0, want=1086378492, limit=525312
    EXT3-fs error (device ubd(98,32)): ext3_get_inode_loc: unable to read inode block – inode=2507, block=808465534
    EXT3-fs error (device ubd(98,32)) in ext3_reserve_inode_write: IO failure
    attempt to access beyond end of device
    62:20: rw=0, want=1086378492, limit=525312
    EXT3-fs error (device ubd(98,32)): ext3_get_inode_loc: unable to read inode block – inode=2507, block=808465534
    EXT3-fs error (device ubd(98,32)) in ext3_reserve_inode_write: IO failure
    attempt to access beyond end of device
    62:20: rw=0, want=1086378492, limit=525312
    EXT3-fs error (device ubd(98,32)): ext3_get_inode_loc: unable to read inode block – inode=2507, block=808465534
    EXT3-fs error (device ubd(98,32)) in ext3_reserve_inode_write: IO failure

    Over and over and over, and I/O failures on files. I’m turning it back off..

  3. Author Photo

    Well then. Let me gather the info and send that along to the list.

    -Chris

  4. Author Photo

    My var filesystem was pretty goofed up, but I managed to fix it, and am up and running again without mmap.

  5. Author Photo

    Thanks for giving it a try. Glad it wasn’t too hosed… I guess there is our answer about mmap. It’s hungry for filesystems!

    I’ve posted a msg to uml-user, so we’ll see what comes of it. I also removed the option from the config edit page…

    Thanks,
    -Chris

  6. Author Photo

    Not a problem, I was prepared if it had gone worse. I saw your email, I’ll be interested to see if they can track down the problem.. It’s an interesting option that I’d like to use on my non-linode UML’s as well.

  7. Author Photo

    Sounds like Jeff knows what to look for (from #uml)…

    [code]13:05 < caker> jdike: anything else I can provide on the ubd=mmap corruption issue?
    13:33 < jdike> caker: I’ve seen problems, so I’ve got something to chase
    13:33 < jdike> caker: namely pages of zeros which shouldn’t be[/code]
    -Chris

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