Re: [PATCH v4 -mm] make swapin readahead skip over holes
From: Andrew Morton <akpm@linux-foundation.org>
Date: 2012-01-26 01:23:22
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On Tue, 24 Jan 2012 14:14:00 -0500 Rik van Riel [off-list ref] 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...
quoted hunk ↗ jump to hunk
--- 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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