mm: mmu_gather rework

Rework the existing mmu_gather infrastructure.

The direct purpose of these patches was to allow preemptible mmu_gather,
but even without that I think these patches provide an improvement to the
status quo.

The first 9 patches rework the mmu_gather infrastructure.  For review
purpose I've split them into generic and per-arch patches with the last of
those a generic cleanup.

The next patch provides generic RCU page-table freeing, and the followup
is a patch converting s390 to use this.  I've also got 4 patches from
DaveM lined up (not included in this series) that uses this to implement
gup_fast() for sparc64.

Then there is one patch that extends the generic mmu_gather batching.

After that follow the mm preemptibility patches, these make part of the mm
a lot more preemptible.  It converts i_mmap_lock and anon_vma->lock to
mutexes which together with the mmu_gather rework makes mmu_gather
preemptible as well.

Making i_mmap_lock a mutex also enables a clean-up of the truncate code.

This also allows for preemptible mmu_notifiers, something that XPMEM I
think wants.

Furthermore, it removes the new and universially detested unmap_mutex.

This patch:

Remove the first obstacle towards a fully preemptible mmu_gather.

The current scheme assumes mmu_gather is always done with preemption
disabled and uses per-cpu storage for the page batches.  Change this to
try and allocate a page for batching and in case of failure, use a small
on-stack array to make some progress.

Preemptible mmu_gather is desired in general and usable once i_mmap_lock
becomes a mutex.  Doing it before the mutex conversion saves us from
having to rework the code by moving the mmu_gather bits inside the
pte_lock.

Also avoid flushing the tlb batches from under the pte lock, this is
useful even without the i_mmap_lock conversion as it significantly reduces
pte lock hold times.

[akpm@linux-foundation.org: fix comment tpyo]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: David Miller <davem@davemloft.net>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Tony Luck <tony.luck@intel.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Hugh Dickins <hughd@google.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Namhyung Kim <namhyung@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 9 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index adb12527fd0e..40d49986e714 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1903,17 +1903,17 @@ static void unmap_region(struct mm_struct *mm,
                 unsigned long start, unsigned long end)
 {
         struct vm_area_struct *next = prev? prev->vm_next: mm->mmap;
-        struct mmu_gather *tlb;
+        struct mmu_gather tlb;
         unsigned long nr_accounted = 0;
 
         lru_add_drain();
-        tlb = tlb_gather_mmu(mm, 0);
+        tlb_gather_mmu(&tlb, mm, 0);
         update_hiwater_rss(mm);
         unmap_vmas(&tlb, vma, start, end, &nr_accounted, NULL);
         vm_unacct_memory(nr_accounted);
-        free_pgtables(tlb, vma, prev? prev->vm_end: FIRST_USER_ADDRESS,
-                                 next? next->vm_start: 0);
-        tlb_finish_mmu(tlb, start, end);
+        free_pgtables(&tlb, vma, prev ? prev->vm_end : FIRST_USER_ADDRESS,
+                                 next ? next->vm_start : 0);
+        tlb_finish_mmu(&tlb, start, end);
 }
 
 /*
@@ -2255,7 +2255,7 @@ EXPORT_SYMBOL(do_brk);
 /* Release all mmaps. */
 void exit_mmap(struct mm_struct *mm)
 {
-        struct mmu_gather *tlb;
+        struct mmu_gather tlb;
         struct vm_area_struct *vma;
         unsigned long nr_accounted = 0;
         unsigned long end;
@@ -2280,14 +2280,14 @@ void exit_mmap(struct mm_struct *mm)
 
         lru_add_drain();
         flush_cache_mm(mm);
-        tlb = tlb_gather_mmu(mm, 1);
+        tlb_gather_mmu(&tlb, mm, 1);
         /* update_hiwater_rss(mm) here? but nobody should be looking */
         /* Use -1 here to ensure all VMAs in the mm are unmapped */
         end = unmap_vmas(&tlb, vma, 0, -1, &nr_accounted, NULL);
         vm_unacct_memory(nr_accounted);
 
-        free_pgtables(tlb, vma, FIRST_USER_ADDRESS, 0);
-        tlb_finish_mmu(tlb, 0, end);
+        free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, 0);
+        tlb_finish_mmu(&tlb, 0, end);
 
         /*
          * Walk the list again, actually closing and freeing it,