Jens Axboe <axboe@suse.de> wrote:
>
> On Wed, Jul 16 2003, Andrea Arcangeli wrote:
> > On Wed, Jul 16, 2003 at 02:46:56PM +0200, Jens Axboe wrote:
> > > Well it's a combined problem. Threshold too high on dirty memory,
> > > someone doing a read well get stuck flushing out as well.
> >
> > a pure read not. the write throttling should be per-process, then there
> > will be little risk.
>
> A read from user space, dirtying data along the way.
Actually it's a read from userspace which allocates a page which goes into
direct reclaim which discovers a locked buffer on the tail of the LRU and
then waits on it.
And if he's especially unlucky: while he waits, some other process
continues to pound more writes into the queue which get merged ahead of the
one he's waiting on, up to a point.
(I don't know if 2.6 does much better in this regard. It is supposed to.
Has anyone tested for it?)
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This archive was generated by hypermail 2b29 : Wed Jul 23 2003 - 22:00:25 EST