Chris Mason wrote:
>
> On Sat, 10 Jun 2000, David Gould wrote:
>
> > On Fri, Jun 09, 2000 at 12:44:19PM +0100, Stephen C. Tweedie wrote:
> > > Hi,
> > >
> > > On Fri, Jun 09, 2000 at 12:45:51PM +0200, Xuan Baldauf wrote:
> > > >
> > > > Is it reasonable to use the 50 bytes of /dev/nvram for logging or is it just
> > > > too small?
> > >
> > > Far, far, far, far, far too small. You need tens of kB minimum to record
> > > a single filesystem transaction for a complex operation such as a file
> > > delete.
> >
> > Interesting. Or even surprising. I suppose I could just go read the code,
> > but for instant gratification of my curiousity, I will ask here first.
> >
> > What exactly is being logged for a file deletion that takes so much space?
> >
> > Is this for the general case, or only for files with a lot of indirect
> > blocks?
> >
>
> It is the same with reiserfs, we log blocks, and each block is 4k.
> Deleting a large file (>2GB) could touch thousands of blocks. These can
> be broken up into multiple transcations, but even then it could touch 15
> or 16 blocks at a time.
>
> But, the other reason you don't want a tiny log is the log limits how long
> you can go without flushing the metadata to its real location on disk. If
> your log fills in 1 second and you have to start flushing, performance
> will suffer badly.
>
> -chris
Doing small syncs is like having a small log. Batching the fsyncs should be
like increasing the log size. Very loosely speaking....
Hans
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