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swapin: fix valid_swaphandles defect

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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: Hugh Dickins <hugh@veritas.com>
Acked-by: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins
2008-02-04 22:28:45 -08:00
committed by Linus Torvalds
parent 5402b976ae
commit 8952898b0d
1 changed files with 34 additions and 17 deletions
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51
mm/swapfile.c
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@ -1769,31 +1769,48 @@ get_swap_info_struct(unsigned type)
*/ */
int valid_swaphandles(swp_entry_t entry, unsigned long *offset) int valid_swaphandles(swp_entry_t entry, unsigned long *offset)
{ {
struct swap_info_struct *si;
int our_page_cluster = page_cluster; int our_page_cluster = page_cluster;
int ret = 0, i = 1 << our_page_cluster; pgoff_t target, toff;
unsigned long toff; pgoff_t base, end;
struct swap_info_struct *swapdev = swp_type(entry) + swap_info; int nr_pages = 0;
if (!our_page_cluster) /* no readahead */ if (!our_page_cluster) /* no readahead */
return 0; return 0;
toff = (swp_offset(entry) >> our_page_cluster) << our_page_cluster;
if (!toff) /* first page is swap header */ si = &swap_info[swp_type(entry)];
toff++, i--; target = swp_offset(entry);
*offset = toff; 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); spin_lock(&swap_lock);
do { if (end > si->max) /* don't go beyond end of map */
/* Don't read-ahead past the end of the swap area */ end = si->max;
if (toff >= swapdev->max)
break; /* Count contiguous allocated slots above our target */
for (toff = target; ++toff < end; nr_pages++) {
/* Don't read in free or bad pages */ /* Don't read in free or bad pages */
if (!swapdev->swap_map[toff]) if (!si->swap_map[toff])
break; break;
if (swapdev->swap_map[toff] == SWAP_MAP_BAD) if (si->swap_map[toff] == SWAP_MAP_BAD)
break; break;
toff++; }
ret++; /* Count contiguous allocated slots below our target */
} while (--i); for (toff = target; --toff >= base; 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;
}
spin_unlock(&swap_lock); 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;
} }