Re: [PATCH v4 0/9] mm/swap: Regular page swap optimizations

Minchan Kim
2017-01-03T04:34:32Z

Hi Jan,

On Mon, Jan 02, 2017 at 04:48:41PM +0100, Jan Kara wrote:
> Hi,
>
> On Tue 27-12-16 16:45:03, Minchan Kim wrote:
> > > Patch 3 splits the swap cache radix tree into 64MB chunks, reducing
> > > the rate that we have to contende for the radix tree.
> >
> > To me, it's rather hacky. I think it might be common problem for page cache
> > so can we think another generalized way like range_lock? Ccing Jan.
>
> I agree on the hackyness of the patch and that page cache would suffer with
> the same contention (although the files are usually smaller than swap so it
> would not be that visible I guess). But I don't see how range lock would
> help here - we need to serialize modifications of the tree structure itself
> and that is difficult to achieve with the range lock. So what you would
> need is either a different data structure for tracking swap cache entries
> or a finer grained locking of the radix tree.

Thanks for the comment, Jan.

I think there are more general options. One is to shrink batching pages like
Mel and Tim had approached.

https://patchwork.kernel.org/patch/9008421/
https://patchwork.kernel.org/patch/9322793/

Or concurrent page cache by peter.

https://www.kernel.org/doc/ols/2007/ols2007v2-pages-311-318.pdf

Ccing Nick who might have an interest on lockless page cache.

Thanks.