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SubjectRe: fsync on large files


On Mon, 15 Feb 1999, Theodore Y. Ts'o wrote:
>
> So you mean moving the dirty list into the filesystme-generic portion of
> the inode structure, instead of being an ext2-specific hack? That seems
> quite reasonable.

Yes.

> list. What I'm currently thinking about is to make the filesystem
> allocate memory for storing the dirty list, and allow the filesystem
> decide what an appropriate number of blocks to allow to be stored in the
> dirty list. Most files never have fsync() called upon them, so a way we
> can make things efficient is to only create the dirty list after the
> first call to fsync() on an inode. The first fsync() can then either go
> through all of the indirect blocks, or cause a forced fsync_dev if that
> would be more efficient. That way, for files which don't get
> fsync()'ed, we don't have the overhead of keeping and maintaining the
> dirty list.
>
> Does this sound like a reasonable design?

Ugh.

I'd much rather just always add it to the "inode dirty list". List
maintenance is essentially zero overhead if you use the nice list macros
in <linux/list.h> (as opposed to the braindamaged BSD compatibility macros
in <linux/lists.h>), and it's fairly trivial to just keep each dirty block
on two dirty lists (one inode-specific, one global - you'd still use the
global one for normal write-outs).

It's just a few pointer operations, and the advantage of having a clean
and simple design probably results in better performance anyway.

Linus


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