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mm: make swapin readahead skip over holes

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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: Rik van Riel <riel@redhat.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Adrian Drzewiecki <z@drze.net>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Rik van Riel
2012-03-21 16:33:50 -07:00
committed by Linus Torvalds
parent c38446cc65
commit 67f96aa252
3 changed files with 11 additions and 66 deletions
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mm/swapfile.c
-52
View File
@@ -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