Re: [PATCH v2 -mm] make swapin readahead skip over holes

[Rik van Riel]

On 01/11/2012 04:10 PM, Johannes Weiner wrote:
> On Wed, Jan 11, 2012 at 02:30:44PM -0500, Rik van Riel wrote:
> > Ever since abandoning the virtual scan of processes, for scalability
> > reasons, swap space has been a little more fragmented than before.
> > This can lead to the situation where a large memory user is killed,
> > swap space ends up full of "holes" and swapin readahead is totally
> > ineffective.
> >
> > On my home system, after killing a leaky firefox it took over an
> > hour to page just under 2GB of memory back in, slowing the virtual
> > machines down to a crawl.
> >
> > This patch makes swapin readahead simply skip over holes, instead
> > of stopping at them.  This allows the system to swap things back in
> > at rates of several MB/second, instead of a few hundred kB/second.
> >
> > The checks done in valid_swaphandles are already done in
> > read_swap_cache_async as well, allowing us to remove a fair amount
> > of code.
>
> __swap_duplicate() also checks for whether the offset is within the
> swap device range.  Do you think we could remove get_swap_cluster()
> altogether and just try reading the aligned page_cluster range?

That is how I implemented it originally, but we need
to take the swap_lock so it is cleaner to implement
a helper function in swapfile.c :)

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/