mm: Preemptibility -v7 [LWN.net]

From:		Peter Zijlstra <a.p.zijlstra@chello.nl>
To:		Andrea Arcangeli <aarcange@redhat.com>, Avi Kivity <avi@redhat.com>, Thomas Gleixner <tglx@linutronix.de>, Rik van Riel <riel@redhat.com>, Ingo Molnar <mingo@elte.hu>, akpm@linux-foundation.org, Linus Torvalds <torvalds@linux-foundation.org>
Subject:		[PATCH 00/25] mm: Preemptibility -v7
Date:		Tue, 25 Jan 2011 18:31:11 +0100
Message-ID:		<20110125173111.720927511@chello.nl>
Cc:		linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, Benjamin Herrenschmidt <benh@kernel.crashing.org>, David Miller <davem@davemloft.net>, Hugh Dickins <hugh.dickins@tiscali.co.uk>, Mel Gorman <mel@csn.ul.ie>, Nick Piggin <npiggin@kernel.dk>, Peter Zijlstra <a.p.zijlstra@chello.nl>, Paul McKenney <paulmck@linux.vnet.ibm.com>, Yanmin Zhang <yanmin_zhang@linux.intel.com>
Archive-link:		Article, Thread


This patch-set makes part of the mm a lot more preemptible. It converts
i_mmap_lock and anon_vma->lock to mutexes and makes mmu_gather fully
preemptible.

The main motivation was making mm_take_all_locks() preemptible, since it
appears people are nesting hundreds of spinlocks there.

The side-effects are that can finally make mmu_gather preemptible,
something which lots of people have wanted to do for a long time.

It also gets us anon_vma refcounting, which seems to result in a nice
cleanup of the anon_vma lifetime rules wrt KSM and compaction.

This patch-set is build and boot-tested on x86_64 (a previous version was
also tested on Dave's Niagra2 machines, and I suppose s390 was too when
Martin provided the conversion patch for his arch).

There are no known architectures left unconverted.

Yanmin ran the -v3 posting through the comprehensive Intel test farm
and didn't find any regressions.

( Not included in this posting are the 4 Sparc64 patches that implement
  gup_fast, those can be applied separately after this series gets
  anywhere. )

The full series (including the Sparc64 gup_fast bits) also available in -git
form from (against something post .38-rc2):

  git://git.kernel.org/pub/scm/linux/kernel/git/peterz/linux-2.6-mmu_preempt.git


Changes since -v6:

Suggested by Hugh:
 - reordered the patches
 - changed to GFP_NOWAIT | __GFP_NOWARN to allocate mmu_gather pages
 - s/lock/mutex/ for the spinlock to mutex conversion
 - removed all DEFINE_PER_CPU(struct mmu_gather, mmu_gather) remnants
 - split the i_mmap_lock and anon_vma->lock conversion
 - removed some KSM wrappers
 - avoid tlb_flush_mmu() while holding pte_lock

Other:
 - remove the i_mmap_lock lockbreak in truncate (XXX)
 - arch/tile __pte_free_tlb() change

TODO:
 - decide if we want to actually remove the i_mmap_lock lockbreak
 - figure out if LOCK vs MB works or add a smp_mb() to patch #23
 - figure out what to do with sparc's tlb_batch lack of ->fullmm


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