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SubjectRe: Blocked processes <=> Elevator starvation?
On Fri, Oct 27 2000, Rui Sousa wrote:
> I finally had time to give this a better look. It now seems the problem
> is in the VM system.
> I patched a test10-pre4 kernel with kdb, then started two "diff -ur
> linux-2.4.0testX linux-2.4.0testY > log1" and two "find / -true >
> log". After this I tried cat"ing" a small file. The cat never
> returned. At this point I entered kdb and did a stack trace on the "cat"
> process:
> schedule()
> ___wait_on_page()
> do_generic_file_read()
> generic_file_read()
> sys_read()
> system_call()
> So it seems the process is either in a loop in ___wait_on_page()
> racing for the PageLock or it never wakes-up... (I guess I could add a
> printk to check which)
> Unfortunately I didn't find anything obviously wrong with the code.
> I hope you can do a better job tracking the problem down.

Rik is right, just because you are seeing long waits on wait_on_page
doesn't make it a vm problem. When a I/O on a page completes, the
page will be unlocked and wait_on_page can grab it -- so I/O stalls
would results in this behaviour.

Could you try this patch:


and see if it makes a difference?

* Jens Axboe <>
* SuSE Labs
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