Re: [PATCH 00/17] mm: mmu_gather rework

[Peter Zijlstra]

On Thu, 2011-02-17 at 17:23 +0100, Peter Zijlstra wrote:
> s390 wants a bit more, but more on that in another email.

So what s390 wants is something like the below, where a fullmm gather
flushes a-priory and then simply gathers and frees the pages.

I can't see why something like this shouldn't work on x86 and power (the
only two archs I really looked in depth at), but it certainly is
something that needs a close look.

---
Index: linux-2.6/include/asm-generic/tlb.h
===================================================================
--- linux-2.6.orig/include/asm-generic/tlb.h
+++ linux-2.6/include/asm-generic/tlb.h
@@ -145,7 +145,10 @@ tlb_gather_mmu(struct mmu_gather *tlb, s
 	tlb->need_flush = 0;
 	if (num_online_cpus() == 1)
 		tlb->fast_mode = 1;
+
 	tlb->fullmm = full_mm_flush;
+	if (tlb->fullmm)
+		tlb_flush(tlb);
 
 	tlb->local.next = NULL;
 	tlb->local.nr   = 0;
@@ -162,13 +165,15 @@ tlb_flush_mmu(struct mmu_gather *tlb)
 {
 	struct mmu_gather_batch *batch;
 
-	if (!tlb->need_flush)
-		return;
-	tlb->need_flush = 0;
-	tlb_flush(tlb);
+	if (tlb->need_flush && !tlb->fullmm) {
+		tlb_flush(tlb);
+		tlb->need_flush = 0;
+	}
+
 #ifdef CONFIG_HAVE_RCU_TABLE_FREE
 	tlb_table_flush(tlb);
 #endif
+
 	if (tlb_fast_mode(tlb))
 		return;
 

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