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Commit 67f96aa2 authored by Rik van Riel's avatar Rik van Riel Committed by Linus Torvalds
Browse files

mm: make swapin readahead skip over holes 



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.

[akpm@linux-foundation.org: fix it for page_cluster >= 32]
Signed-off-by: default avatarRik van Riel <riel@redhat.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Acked-by: default avatarMel Gorman <mgorman@suse.de>
Cc: Adrian Drzewiecki <z@drze.net>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c38446cc

include/linux/swap.h

+0 −1
Original line number Diff line number Diff line
@@ -329,7 +329,6 @@ extern long total_swap_pages; 
extern void si_swapinfo(struct sysinfo *);

extern swp_entry_t get_swap_page(void);

extern swp_entry_t get_swap_page_of_type(int);

extern int valid_swaphandles(swp_entry_t, unsigned long *);

extern int add_swap_count_continuation(swp_entry_t, gfp_t);

extern void swap_shmem_alloc(swp_entry_t);

extern int swap_duplicate(swp_entry_t);

mm/swap_state.c

+11 −13
Original line number Diff line number Diff line
@@ -372,25 +372,23 @@ 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 = (1UL << page_cluster) - 1;



	/*

	 * Get starting offset for readaround, and number of pages to read.

	 * Adjust starting address by readbehind (for NUMA interleave case)?

	 * No, it's very unlikely that swap layout would follow vma layout,

	 * more likely that neighbouring swap pages came from the same node:

	 * so use the same "addr" to choose the same node for each swap read.

	 */

	nr_pages = valid_swaphandles(entry, &offset);

	for (end_offset = offset + nr_pages; offset < end_offset; offset++) {

	/* Read a page_cluster sized and aligned cluster around offset. */

	start_offset = offset & ~mask;

	end_offset = offset | mask;

	if (!start_offset)	/* First page is swap header. */

		start_offset++;



	for (offset = start_offset; offset <= end_offset ; offset++) {

		/* Ok, do the async read-ahead now */

		page = read_swap_cache_async(swp_entry(swp_type(entry), offset),

						gfp_mask, vma, addr);

		if (!page)

			break;

			continue;

		page_cache_release(page);

	}

	lru_add_drain();	/* Push any new pages onto the LRU now */

mm/swapfile.c

+0 −52
Original line number Diff line number Diff line
@@ -2287,58 +2287,6 @@ int swapcache_prepare(swp_entry_t entry) 
	return __swap_duplicate(entry, SWAP_HAS_CACHE);

}



/*

 * swap_lock prevents swap_map being freed. Don't grab an extra

 * reference on the swaphandle, it doesn't matter if it becomes unused.

 */

int valid_swaphandles(swp_entry_t entry, unsigned long *offset)

{

	struct swap_info_struct *si;

	int our_page_cluster = page_cluster;

	pgoff_t target, toff;

	pgoff_t base, end;

	int nr_pages = 0;



	if (!our_page_cluster)	/* no readahead */

		return 0;



	si = swap_info[swp_type(entry)];

	target = swp_offset(entry);

	base = (target >> our_page_cluster) << our_page_cluster;

	end = base + (1 << our_page_cluster);

	if (!base)		/* first page is swap header */

		base++;



	spin_lock(&swap_lock);

	if (end > si->max)	/* don't go beyond end of map */

		end = si->max;



	/* Count contiguous allocated slots above our target */

	for (toff = target; ++toff < end; nr_pages++) {

		/* Don't read in free or bad pages */

		if (!si->swap_map[toff])

			break;

		if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD)

			break;

	}

	/* Count contiguous allocated slots below our target */

	for (toff = target; --toff >= base; nr_pages++) {

		/* Don't read in free or bad pages */

		if (!si->swap_map[toff])

			break;

		if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD)

			break;

	}

	spin_unlock(&swap_lock);



	/*

	 * Indicate starting offset, and return number of pages to get:

	 * if only 1, say 0, since there's then no readahead to be done.

	 */

	*offset = ++toff;

	return nr_pages? ++nr_pages: 0;

}



/*

 * add_swap_count_continuation - called when a swap count is duplicated

 * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's