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)
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..
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..
Well then. Let me gather the info and send that along to the list.
-Chris
My var filesystem was pretty goofed up, but I managed to fix it, and am up and running again without mmap.
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
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.
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