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author | Hugh Dickins <hugh@veritas.com> | 2008-02-04 22:28:45 -0800 |
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committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2008-02-05 09:44:15 -0800 |
commit | 8952898b0d25223f38daf46b86156fd1c4d17ad0 (patch) | |
tree | 10912460cd9d42195d4aba8250ed1c3bd3577bb4 | |
parent | 5402b976ae0be96b3a32f3508ab7308c380d6477 (diff) | |
download | op-kernel-dev-8952898b0d25223f38daf46b86156fd1c4d17ad0.zip op-kernel-dev-8952898b0d25223f38daf46b86156fd1c4d17ad0.tar.gz |
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: 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>
-rw-r--r-- | mm/swapfile.c | 49 |
1 files changed, 33 insertions, 16 deletions
diff --git a/mm/swapfile.c b/mm/swapfile.c index ab93505..f5ba723 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -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; } |