Re: [RFC] mlock: release mmap_sem every 256 faulted pages

[Andrew Morton]

On Mon, 22 Nov 2010 21:00:52 -0800 Michel Lespinasse <walken@xxxxxxxxxx> wrote:

> Hi,
> 
> I'd like to sollicit comments on this proposal:
> 
> Currently mlock() holds mmap_sem in exclusive mode while the pages get
> faulted in. In the case of a large mlock, this can potentially take a
> very long time.

A more compelling description of why this problem needs addressing
would help things along.

> +		/*
> +		 * Limit batch size to 256 pages in order to reduce
> +		 * mmap_sem hold time.
> +		 */
> +		nfault = nstart + 256 * PAGE_SIZE;

It would be nicer if there was an rwsem API to ask if anyone is
currently blocked in down_read() or down_write().  That wouldn't be too
hard to do.  It wouldn't detect people polling down_read_trylock() or
down_write_trylock() though.
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