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authorDan Streetman <ddstreet@ieee.org>2014-06-04 16:09:53 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-06-04 16:54:07 -0700
commitadfab836f4908deb049a5128082719e689eed964 (patch)
tree345475c5282e96791fe3bce8f0287674fa9acc1d /mm/frontswap.c
parent7ee07a44eb53374a73544ae14c71366a02d462e0 (diff)
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swap: change swap_info singly-linked list to list_head
The logic controlling the singly-linked list of swap_info_struct entries for all active, i.e. swapon'ed, swap targets is rather complex, because: - it stores the entries in priority order - there is a pointer to the highest priority entry - there is a pointer to the highest priority not-full entry - there is a highest_priority_index variable set outside the swap_lock - swap entries of equal priority should be used equally this complexity leads to bugs such as: https://lkml.org/lkml/2014/2/13/181 where different priority swap targets are incorrectly used equally. That bug probably could be solved with the existing singly-linked lists, but I think it would only add more complexity to the already difficult to understand get_swap_page() swap_list iteration logic. The first patch changes from a singly-linked list to a doubly-linked list using list_heads; the highest_priority_index and related code are removed and get_swap_page() starts each iteration at the highest priority swap_info entry, even if it's full. While this does introduce unnecessary list iteration (i.e. Schlemiel the painter's algorithm) in the case where one or more of the highest priority entries are full, the iteration and manipulation code is much simpler and behaves correctly re: the above bug; and the fourth patch removes the unnecessary iteration. The second patch adds some minor plist helper functions; nothing new really, just functions to match existing regular list functions. These are used by the next two patches. The third patch adds plist_requeue(), which is used by get_swap_page() in the next patch - it performs the requeueing of same-priority entries (which moves the entry to the end of its priority in the plist), so that all equal-priority swap_info_structs get used equally. The fourth patch converts the main list into a plist, and adds a new plist that contains only swap_info entries that are both active and not full. As Mel suggested using plists allows removing all the ordering code from swap - plists handle ordering automatically. The list naming is also clarified now that there are two lists, with the original list changed from swap_list_head to swap_active_head and the new list named swap_avail_head. A new spinlock is also added for the new list, so swap_info entries can be added or removed from the new list immediately as they become full or not full. This patch (of 4): Replace the singly-linked list tracking active, i.e. swapon'ed, swap_info_struct entries with a doubly-linked list using struct list_heads. Simplify the logic iterating and manipulating the list of entries, especially get_swap_page(), by using standard list_head functions, and removing the highest priority iteration logic. The change fixes the bug: https://lkml.org/lkml/2014/2/13/181 in which different priority swap entries after the highest priority entry are incorrectly used equally in pairs. The swap behavior is now as advertised, i.e. different priority swap entries are used in order, and equal priority swap targets are used concurrently. Signed-off-by: Dan Streetman <ddstreet@ieee.org> Acked-by: Mel Gorman <mgorman@suse.de> Cc: Shaohua Li <shli@fusionio.com> Cc: Hugh Dickins <hughd@google.com> Cc: Dan Streetman <ddstreet@ieee.org> Cc: Michal Hocko <mhocko@suse.cz> Cc: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com> Cc: Weijie Yang <weijieut@gmail.com> Cc: Rik van Riel <riel@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Bob Liu <bob.liu@oracle.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/frontswap.c')
-rw-r--r--mm/frontswap.c13
1 files changed, 4 insertions, 9 deletions
diff --git a/mm/frontswap.c b/mm/frontswap.c
index 1b24bdcb3197..fae11602e8a9 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -327,15 +327,12 @@ EXPORT_SYMBOL(__frontswap_invalidate_area);
static unsigned long __frontswap_curr_pages(void)
{
- int type;
unsigned long totalpages = 0;
struct swap_info_struct *si = NULL;
assert_spin_locked(&swap_lock);
- for (type = swap_list.head; type >= 0; type = si->next) {
- si = swap_info[type];
+ list_for_each_entry(si, &swap_list_head, list)
totalpages += atomic_read(&si->frontswap_pages);
- }
return totalpages;
}
@@ -347,11 +344,9 @@ static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
int si_frontswap_pages;
unsigned long total_pages_to_unuse = total;
unsigned long pages = 0, pages_to_unuse = 0;
- int type;
assert_spin_locked(&swap_lock);
- for (type = swap_list.head; type >= 0; type = si->next) {
- si = swap_info[type];
+ list_for_each_entry(si, &swap_list_head, list) {
si_frontswap_pages = atomic_read(&si->frontswap_pages);
if (total_pages_to_unuse < si_frontswap_pages) {
pages = pages_to_unuse = total_pages_to_unuse;
@@ -366,7 +361,7 @@ static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
}
vm_unacct_memory(pages);
*unused = pages_to_unuse;
- *swapid = type;
+ *swapid = si->type;
ret = 0;
break;
}
@@ -413,7 +408,7 @@ void frontswap_shrink(unsigned long target_pages)
/*
* we don't want to hold swap_lock while doing a very
* lengthy try_to_unuse, but swap_list may change
- * so restart scan from swap_list.head each time
+ * so restart scan from swap_list_head each time
*/
spin_lock(&swap_lock);
ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);