Re: Unresponiveness of 2.4.16

[Andrew Morton]

Marcelo Tosatti wrote:
> 
> > ...
> > But so little code is actually using READA at this stage that I didn't
> > bother - I first need to go through those paths and make sure that they
> > are in fact complete, working and useful...
> 
> I've done some experiments in the past which have shown that doing this
> will cause us to almost _never_ do readahead on IO intensive workloads,
> which ended up decreasing performance instead increasing it.

Interesting.  Thanks.

One _could_ make the first readahead page non-READA, and then
make the rest READA.  That way, all block-contiguous requests
will be merged, and any non-contiguous requests will be dropped on
the floor if the request queue is full.  Which is probably what
we want to happen anyway.

Of course the alternative is to slot a little bmap() call into
the readhead logic :)

> Please make sure to extensively test the propagation of READA through the
> pagecache when you do so...

Extensivelytest is my middle name.

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