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Re: ext3 blocks other with large writes


On Thu, Feb 28, 2002 at 01:30:13PM -0800, Andrew Morton wrote:

> There are a few things you can do:
> You'll want
> http://www.zip.com.au/~akpm/linux/patches/2.4/2.4.18-rc1/make_request.patch
> to fix the elevator starvation problem.  This is officially in 2.4.19-pre1.

>From which:

+ *    a) A READA requester fails if free_requests < batch_requests
+ * 
+ *       We don't want READA requests to prevent sleepers from ever
+ *       waking.  Note that READA is used extremely rarely - a few
+ *       filesystems use it for directory readahead.

I'd actually like to see READA used more, but isn't it dangerous to
drop such requests?  Under high IO load, readahead is actually likely
to reduce the number of seeks we incur, so surely it gets more, not
less, important to honour readahead as the IO queues fill up?


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