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Commit 8952898b authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

swapin: fix valid_swaphandles defect 



valid_swaphandles is supposed to do a quick pass over the swap map entries
neigbouring the entry which swapin_readahead is targetting, to determine for
it a range worth reading all together.  But since it always starts its search
from the beginning of the swap "cluster", a reject (free entry) there
immediately curtails the readaround, and every swapin_readahead from that
cluster is for just a single page.  Instead scan forwards and backwards around
the target entry.

Use better names for some variables: a swap_info pointer is usually called
"si" not "swapdev".  And at the end, if only the target page should be read,
return count of 0 to disable readaround, to avoid the unnecessarily repeated
call to read_swap_cache_async.

Signed-off-by: default avatarHugh Dickins <hugh@veritas.com>
Acked-by: default avatarRik van Riel <riel@surriel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5402b976

mm/swapfile.c

+33 −16
Original line number Diff line number Diff line
@@ -1769,31 +1769,48 @@ get_swap_info_struct(unsigned type) 
 */

int valid_swaphandles(swp_entry_t entry, unsigned long *offset)

{

	struct swap_info_struct *si;

	int our_page_cluster = page_cluster;

	int ret = 0, i = 1 << our_page_cluster;

	unsigned long toff;

	struct swap_info_struct *swapdev = swp_type(entry) + swap_info;

	pgoff_t target, toff;

	pgoff_t base, end;

	int nr_pages = 0;



	if (!our_page_cluster)	/* no readahead */

		return 0;

	toff = (swp_offset(entry) >> our_page_cluster) << our_page_cluster;

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

		toff++, i--;

	*offset = toff;



	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);

	do {

		/* Don't read-ahead past the end of the swap area */

		if (toff >= swapdev->max)

	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 (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 (!swapdev->swap_map[toff])

		if (!si->swap_map[toff])

			break;

		if (swapdev->swap_map[toff] == SWAP_MAP_BAD)

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

			break;

		toff++;

		ret++;

	} while (--i);

	}

	spin_unlock(&swap_lock);

	return ret;



	/*

	 * 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;

}