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authorMatthew Wilcox <mawilcox@microsoft.com>2016-12-14 15:08:49 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-12-14 16:04:10 -0800
commit148deab223b23734069abcacb5c7118b0e7deadc (patch)
tree56aae9c91802e9262312f7fcbb3571eb9c8ec0e9 /mm/khugepaged.c
parentb35df27a39f40e39fabf1b1e9569c7b24e1add6a (diff)
radix-tree: improve multiorder iterators
This fixes several interlinked problems with the iterators in the presence of multiorder entries. 1. radix_tree_iter_next() would only advance by one slot, which would result in the iterators returning the same entry more than once if there were sibling entries. 2. radix_tree_next_slot() could return an internal pointer instead of a user pointer if a tagged multiorder entry was immediately followed by an entry of lower order. 3. radix_tree_next_slot() expanded to a lot more code than it used to when multiorder support was compiled in. And I wasn't comfortable with entry_to_node() being in a header file. Fixing radix_tree_iter_next() for the presence of sibling entries necessarily involves examining the contents of the radix tree, so we now need to pass 'slot' to radix_tree_iter_next(), and we need to change the calling convention so it is called *before* dropping the lock which protects the tree. Also rename it to radix_tree_iter_resume(), as some people thought it was necessary to call radix_tree_iter_next() each time around the loop. radix_tree_next_slot() becomes closer to how it looked before multiorder support was introduced. It only checks to see if the next entry in the chunk is a sibling entry or a pointer to a node; this should be rare enough that handling this case out of line is not a performance impact (and such impact is amortised by the fact that the entry we just processed was a multiorder entry). Also, radix_tree_next_slot() used to force a new chunk lookup for untagged entries, which is more expensive than the out of line sibling entry skipping. Link: http://lkml.kernel.org/r/1480369871-5271-55-git-send-email-mawilcox@linuxonhyperv.com Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com> Tested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Konstantin Khlebnikov <koct9i@gmail.com> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Cc: Matthew Wilcox <mawilcox@microsoft.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/khugepaged.c')
-rw-r--r--mm/khugepaged.c7
1 files changed, 3 insertions, 4 deletions
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 7434a63cac94..e32389a97030 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1446,7 +1446,7 @@ static void collapse_shmem(struct mm_struct *mm,
radix_tree_replace_slot(&mapping->page_tree, slot,
new_page + (index % HPAGE_PMD_NR));
- slot = radix_tree_iter_next(&iter);
+ slot = radix_tree_iter_resume(slot, &iter);
index++;
continue;
out_lru:
@@ -1546,7 +1546,6 @@ tree_unlocked:
/* Put holes back where they were */
radix_tree_delete(&mapping->page_tree,
iter.index);
- slot = radix_tree_iter_next(&iter);
continue;
}
@@ -1557,11 +1556,11 @@ tree_unlocked:
page_ref_unfreeze(page, 2);
radix_tree_replace_slot(&mapping->page_tree,
slot, page);
+ slot = radix_tree_iter_resume(slot, &iter);
spin_unlock_irq(&mapping->tree_lock);
putback_lru_page(page);
unlock_page(page);
spin_lock_irq(&mapping->tree_lock);
- slot = radix_tree_iter_next(&iter);
}
VM_BUG_ON(nr_none);
spin_unlock_irq(&mapping->tree_lock);
@@ -1641,8 +1640,8 @@ static void khugepaged_scan_shmem(struct mm_struct *mm,
present++;
if (need_resched()) {
+ slot = radix_tree_iter_resume(slot, &iter);
cond_resched_rcu();
- slot = radix_tree_iter_next(&iter);
}
}
rcu_read_unlock();