linux-kernel - Re: [PATCH 00/17] mm: mmu

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Date:	Thu, 17 Feb 2011 18:42:23 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Avi Kivity <avi@...hat.com>, Thomas Gleixner <tglx@...utronix.de>,
	Rik van Riel <riel@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	akpm@...ux-foundation.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-mm@...ck.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Miller <davem@...emloft.net>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Mel Gorman <mel@....ul.ie>, Nick Piggin <npiggin@...nel.dk>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Yanmin Zhang <yanmin_zhang@...ux.intel.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH 00/17] mm: mmu_gather rework

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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