On Tue, 24 Jan 2012 14:14:00 -0500
Rik van Riel <riel@xxxxxxxxxx> 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.
Just to show that I'm paying attention...
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -382,25 +382,23 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
> struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
> struct vm_area_struct *vma, unsigned long addr)
> {
> - int nr_pages;
> struct page *page;
> - unsigned long offset;
> - unsigned long end_offset;
> + unsigned long offset = swp_offset(entry);
> + unsigned long start_offset, end_offset;
> + unsigned long mask = (1 << page_cluster) - 1;
This is broken for page_cluster > 31. Fix:
--- a/mm/swap_state.c~make-swapin-readahead-skip-over-holes-fix
+++ a/mm/swap_state.c
@@ -385,7 +385,7 @@ struct page *swapin_readahead(swp_entry_
struct page *page;
unsigned long offset = swp_offset(entry);
unsigned long start_offset, end_offset;
- unsigned long mask = (1 << page_cluster) - 1;
+ unsigned long mask = (1UL << page_cluster) - 1;
/* Read a page_cluster sized and aligned cluster around offset. */
start_offset = offset & ~mask;
_
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