Re: reiserfs blocks long on getdents64() during concurrent write

[Roland Kuhn]

On 5 Aug 2002, Chris Mason wrote:

> 01-relocation-4 deals with allowing reiserfs to use an external logging
> device.  It isn't related to your problem, but 02-commit_super-8 is
> diffed against it.
> 
> 02-commit_super-8 does two things.  First it changes sync_supers() so
> that it won't loop on a single filesystem while it's super is dirty. 
> Before, if kupdate triggered a write_super call, and another FS writer
> redirtied the super after write_super cleared it (but before it
> returned), write_super gets called a second time.  Since a commit was
> done for each write_super call, that gets expensive quickly.
> 
> Second, the patch adds a commit_super call, and changes sync() to use
> that instead of write_super.  This allows the FS to skip the commit when
> write_super is called.
> 
> This does lead to fewer commits and longer running transactions, but
> does not increase the amount of time it takes the write() call to
> complete.  It does increase the time between when you make a metadata
> change and when that change actually goes to the disk.  
> 
Ahh, thanks! This sounds like a good idea to me, hopefully your patch will 
be accepted despite the fact that Alan is busy doing other things ;-)

Coming back to the issue: applying these patches increased the throughput
by about 20% :-) Now it takes about 100sec instead of 120sec to write a
2GB file. Tomorrow I will try it without the write_times part, to see how 
much that does.

But more important: the hiccups are more seldom and sometimes shorter than 
before. With plain 2.4.19 I would hit it about twice per minute (I have 
not measured it), now it happens only after two minutes when writing 1M 
chunks at 20MB/s. The longest seen so far was also about 4 seconds, 
though.

Ciao,
					Roland

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