[RFC,1/4] mm: munmap optimise single threaded page freeing

Commit Message

Nicholas Piggin July 25, 2018, 3:52 p.m. UTC

In case a single threaded process is zapping its own mappings, there
should be no concurrent memory accesses through the TLBs, and so it
is safe to free pages immediately rather than batch them up.
---
 mm/memory.c | 9 +++++++++
 1 file changed, 9 insertions(+)

Patch

diff --git a/mm/memory.c b/mm/memory.c
index 135d18b31e44..773d588b371d 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -296,6 +296,15 @@  bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page, int page_
 	VM_BUG_ON(!tlb->end);
 	VM_WARN_ON(tlb->page_size != page_size);
 
+	/*
+	 * When this is our mm and there are no other users, there can not be
+	 * a concurrent memory access.
+	 */
+	if (current->mm == tlb->mm && atomic_read(&tlb->mm->mm_users) < 2) {
+		free_page_and_swap_cache(page);
+		return false;
+	}
+
 	batch = tlb->active;
 	/*
 	 * Add the page and check if we are full. If so