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authorYin Fengwei <fengwei.yin@intel.com>2023-04-29 16:27:58 +0800
committerAndrew Morton <akpm@linux-foundation.org>2023-06-09 16:25:50 -0700
commitdeedad80f660af8199ea3b3f70939f2d226b9154 (patch)
tree0b8de545f9b86f63790213e546a4aa14a3467d95 /mm/huge_memory.c
parenta95722a047724ef75567381976a36f0e44230bd9 (diff)
THP: avoid lock when check whether THP is in deferred list
free_transhuge_page() acquires split queue lock then check whether the THP was added to deferred list or not. It brings high deferred queue lock contention. It's safe to check whether the THP is in deferred list or not without holding the deferred queue lock in free_transhuge_page() because when code hit free_transhuge_page(), there is no one tries to add the folio to _deferred_list. Running page_fault1 of will-it-scale + order 2 folio for anonymous mapping with 96 processes on an Ice Lake 48C/96T test box, we could see the 61% split_queue_lock contention: - 63.02% 0.01% page_fault1_pro [kernel.kallsyms] [k] free_transhuge_page - 63.01% free_transhuge_page + 62.91% _raw_spin_lock_irqsave With this patch applied, the split_queue_lock contention is less than 1%. Link: https://lkml.kernel.org/r/20230429082759.1600796-2-fengwei.yin@intel.com Signed-off-by: Yin Fengwei <fengwei.yin@intel.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reviewed-by: "Huang, Ying" <ying.huang@intel.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Yu Zhao <yuzhao@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/huge_memory.c')
-rw-r--r--mm/huge_memory.c17
1 files changed, 12 insertions, 5 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 624671aaa60d..9ccdb3fe3244 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2792,12 +2792,19 @@ void free_transhuge_page(struct page *page)
struct deferred_split *ds_queue = get_deferred_split_queue(folio);
unsigned long flags;
- spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
- if (!list_empty(&folio->_deferred_list)) {
- ds_queue->split_queue_len--;
- list_del(&folio->_deferred_list);
+ /*
+ * At this point, there is no one trying to add the folio to
+ * deferred_list. If folio is not in deferred_list, it's safe
+ * to check without acquiring the split_queue_lock.
+ */
+ if (data_race(!list_empty(&folio->_deferred_list))) {
+ spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
+ if (!list_empty(&folio->_deferred_list)) {
+ ds_queue->split_queue_len--;
+ list_del(&folio->_deferred_list);
+ }
+ spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
}
- spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
free_compound_page(page);
}