Re: Is ext3 flush data to disk when files are closed?

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On Wed, 19 Oct 2005, Xin Zhao wrote:

> As far as I know, if an application modifies a file on an ext3 file
> ssytem, it actually change the page cache, and the dirty pages will be
> flushed to disk by kupdate periodically.
>
> My question is: if a file is to be closed, but some of its data pages
> are marked as dirty, will system block on close() and wait for dirty
> pages being flushed to disk? If so, it seems to decrease performance
> significantly if a lot of updates on many small files are involved.
>
> Can someone point me to the right place to check how it works? Thanks!
>
> Xin

In principle, if you open a file, write to it, close it, have
somebody else open it, read it, close it, then delete it, it
probably will never touch a physical disk. This is the basic
way a VFS (virtual file system) works. The system maintains a
RAM Disk that overflows to the physical media.

Given that, there are various ways to provoke the system into
writing data to the disk(s), such as executing `sync`. However,
normally file-data are written when the kernel needs to free
up some memory or when the disk(s) are un-mounted.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.13.4 on an i686 machine (5589.55 BogoMips).
Warning : 98.36% of all statistics are fiction.
.

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