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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>
This commit is contained in:
Peter Zijlstra 2011-05-24 17:11:45 -07:00 committed by Linus Torvalds
parent d05f3169c0
commit d16dfc550f
5 changed files with 107 additions and 65 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
fs/exec.c
View File

@ -600,7 +600,7 @@ static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
unsigned long length = old_end - old_start;
unsigned long new_start = old_start - shift;
unsigned long new_end = old_end - shift;
struct mmu_gather *tlb;
struct mmu_gather tlb;
BUG_ON(new_start > new_end);
@ -626,12 +626,12 @@ static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
return -ENOMEM;
lru_add_drain();
tlb = tlb_gather_mmu(mm, 0);
tlb_gather_mmu(&tlb, mm, 0);
if (new_end > old_start) {
/*
* when the old and new regions overlap clear from new_end.
*/
free_pgd_range(tlb, new_end, old_end, new_end,
free_pgd_range(&tlb, new_end, old_end, new_end,
vma->vm_next ? vma->vm_next->vm_start : 0);
} else {
/*
@ -640,10 +640,10 @@ static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
* have constraints on va-space that make this illegal (IA64) -
* for the others its just a little faster.
*/
free_pgd_range(tlb, old_start, old_end, new_end,
free_pgd_range(&tlb, old_start, old_end, new_end,
vma->vm_next ? vma->vm_next->vm_start : 0);
}
tlb_finish_mmu(tlb, new_end, old_end);
tlb_finish_mmu(&tlb, new_end, old_end);
/*
* Shrink the vma to just the new range. Always succeeds.

96
include/asm-generic/tlb.h
View File

@ -5,6 +5,8 @@
* Copyright 2001 Red Hat, Inc.
* Based on code from mm/memory.c Copyright Linus Torvalds and others.
*
* Copyright 2011 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
@ -22,51 +24,71 @@
* and page free order so much..
*/
#ifdef CONFIG_SMP
#ifdef ARCH_FREE_PTR_NR
#define FREE_PTR_NR ARCH_FREE_PTR_NR
#else
#define FREE_PTE_NR 506
#endif
#define tlb_fast_mode(tlb) ((tlb)->nr == ~0U)
#else
#define FREE_PTE_NR 1
#define tlb_fast_mode(tlb) 1
#endif
/*
* If we can't allocate a page to make a big batch of page pointers
* to work on, then just handle a few from the on-stack structure.
*/
#define MMU_GATHER_BUNDLE 8
/* struct mmu_gather is an opaque type used by the mm code for passing around
* any data needed by arch specific code for tlb_remove_page.
*/
struct mmu_gather {
struct mm_struct *mm;
unsigned int nr; /* set to ~0U means fast mode */
unsigned int max; /* nr < max */
unsigned int need_flush;/* Really unmapped some ptes? */
unsigned int fullmm; /* non-zero means full mm flush */
struct page * pages[FREE_PTE_NR];
#ifdef HAVE_ARCH_MMU_GATHER
struct arch_mmu_gather arch;
#endif
struct page **pages;
struct page *local[MMU_GATHER_BUNDLE];
};
/* Users of the generic TLB shootdown code must declare this storage space. */
DECLARE_PER_CPU(struct mmu_gather, mmu_gathers);
static inline void __tlb_alloc_page(struct mmu_gather *tlb)
{
unsigned long addr = __get_free_pages(GFP_NOWAIT | __GFP_NOWARN, 0);
if (addr) {
tlb->pages = (void *)addr;
tlb->max = PAGE_SIZE / sizeof(struct page *);
}
}
/* tlb_gather_mmu
* Return a pointer to an initialized struct mmu_gather.
* Called to initialize an (on-stack) mmu_gather structure for page-table
* tear-down from @mm. The @fullmm argument is used when @mm is without
* users and we're going to destroy the full address space (exit/execve).
*/
static inline struct mmu_gather *
tlb_gather_mmu(struct mm_struct *mm, unsigned int full_mm_flush)
static inline void
tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, bool fullmm)
{
struct mmu_gather *tlb = &get_cpu_var(mmu_gathers);
tlb->mm = mm;
/* Use fast mode if only one CPU is online */
tlb->nr = num_online_cpus() > 1 ? 0U : ~0U;
tlb->max = ARRAY_SIZE(tlb->local);
tlb->pages = tlb->local;
tlb->fullmm = full_mm_flush;
if (num_online_cpus() > 1) {
tlb->nr = 0;
__tlb_alloc_page(tlb);
} else /* Use fast mode if only one CPU is online */
tlb->nr = ~0U;
return tlb;
tlb->fullmm = fullmm;
#ifdef HAVE_ARCH_MMU_GATHER
tlb->arch = ARCH_MMU_GATHER_INIT;
#endif
}
static inline void
tlb_flush_mmu(struct mmu_gather *tlb, unsigned long start, unsigned long end)
tlb_flush_mmu(struct mmu_gather *tlb)
{
if (!tlb->need_flush)
return;
@ -75,6 +97,13 @@ tlb_flush_mmu(struct mmu_gather *tlb, unsigned long start, unsigned long end)
if (!tlb_fast_mode(tlb)) {
free_pages_and_swap_cache(tlb->pages, tlb->nr);
tlb->nr = 0;
/*
* If we are using the local on-stack array of pages for MMU
* gather, try allocating an off-stack array again as we have
* recently freed pages.
*/
if (tlb->pages == tlb->local)
__tlb_alloc_page(tlb);
}
}
@ -85,29 +114,42 @@ tlb_flush_mmu(struct mmu_gather *tlb, unsigned long start, unsigned long end)
static inline void
tlb_finish_mmu(struct mmu_gather *tlb, unsigned long start, unsigned long end)
{
tlb_flush_mmu(tlb, start, end);
tlb_flush_mmu(tlb);
/* keep the page table cache within bounds */
check_pgt_cache();
put_cpu_var(mmu_gathers);
if (tlb->pages != tlb->local)
free_pages((unsigned long)tlb->pages, 0);
}
/* tlb_remove_page
/* __tlb_remove_page
* Must perform the equivalent to __free_pte(pte_get_and_clear(ptep)), while
* handling the additional races in SMP caused by other CPUs caching valid
* mappings in their TLBs.
* mappings in their TLBs. Returns the number of free page slots left.
* When out of page slots we must call tlb_flush_mmu().
*/
static inline void tlb_remove_page(struct mmu_gather *tlb, struct page *page)
static inline int __tlb_remove_page(struct mmu_gather *tlb, struct page *page)
{
tlb->need_flush = 1;
if (tlb_fast_mode(tlb)) {
free_page_and_swap_cache(page);
return;
return 1; /* avoid calling tlb_flush_mmu() */
}
tlb->pages[tlb->nr++] = page;
if (tlb->nr >= FREE_PTE_NR)
tlb_flush_mmu(tlb, 0, 0);
VM_BUG_ON(tlb->nr > tlb->max);
return tlb->max - tlb->nr;
}
/* tlb_remove_page
* Similar to __tlb_remove_page but will call tlb_flush_mmu() itself when
* required.
*/
static inline void tlb_remove_page(struct mmu_gather *tlb, struct page *page)
{
if (!__tlb_remove_page(tlb, page))
tlb_flush_mmu(tlb);
}
/**

2
include/linux/mm.h
View File

@ -906,7 +906,7 @@ int zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
unsigned long size);
unsigned long zap_page_range(struct vm_area_struct *vma, unsigned long address,
unsigned long size, struct zap_details *);
unsigned long unmap_vmas(struct mmu_gather **tlb,
unsigned long unmap_vmas(struct mmu_gather *tlb,
struct vm_area_struct *start_vma, unsigned long start_addr,
unsigned long end_addr, unsigned long *nr_accounted,
struct zap_details *);

46
mm/memory.c
View File

@ -912,12 +912,13 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
long *zap_work, struct zap_details *details)
{
struct mm_struct *mm = tlb->mm;
int force_flush = 0;
pte_t *pte;
spinlock_t *ptl;
int rss[NR_MM_COUNTERS];
init_rss_vec(rss);
again:
pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
arch_enter_lazy_mmu_mode();
do {
@ -974,7 +975,9 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
page_remove_rmap(page);
if (unlikely(page_mapcount(page) < 0))
print_bad_pte(vma, addr, ptent, page);
tlb_remove_page(tlb, page);
force_flush = !__tlb_remove_page(tlb, page);
if (force_flush)
break;
continue;
}
/*
@ -1001,6 +1004,18 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
arch_leave_lazy_mmu_mode();
pte_unmap_unlock(pte - 1, ptl);
/*
* mmu_gather ran out of room to batch pages, we break out of
* the PTE lock to avoid doing the potential expensive TLB invalidate
* and page-free while holding it.
*/
if (force_flush) {
force_flush = 0;
tlb_flush_mmu(tlb);
if (addr != end)
goto again;
}
return addr;
}
@ -1121,17 +1136,14 @@ static unsigned long unmap_page_range(struct mmu_gather *tlb,
* ensure that any thus-far unmapped pages are flushed before unmap_vmas()
* drops the lock and schedules.
*/
unsigned long unmap_vmas(struct mmu_gather **tlbp,
unsigned long unmap_vmas(struct mmu_gather *tlb,
struct vm_area_struct *vma, unsigned long start_addr,
unsigned long end_addr, unsigned long *nr_accounted,
struct zap_details *details)
{
long zap_work = ZAP_BLOCK_SIZE;
unsigned long tlb_start = 0; /* For tlb_finish_mmu */
int tlb_start_valid = 0;
unsigned long start = start_addr;
spinlock_t *i_mmap_lock = details? details->i_mmap_lock: NULL;
int fullmm = (*tlbp)->fullmm;
struct mm_struct *mm = vma->vm_mm;
mmu_notifier_invalidate_range_start(mm, start_addr, end_addr);
@ -1152,11 +1164,6 @@ unsigned long unmap_vmas(struct mmu_gather **tlbp,
untrack_pfn_vma(vma, 0, 0);
while (start != end) {
if (!tlb_start_valid) {
tlb_start = start;
tlb_start_valid = 1;
}
if (unlikely(is_vm_hugetlb_page(vma))) {
/*
* It is undesirable to test vma->vm_file as it
@ -1177,7 +1184,7 @@ unsigned long unmap_vmas(struct mmu_gather **tlbp,
start = end;
} else
start = unmap_page_range(*tlbp, vma,
start = unmap_page_range(tlb, vma,
start, end, &zap_work, details);
if (zap_work > 0) {
@ -1185,19 +1192,13 @@ unsigned long unmap_vmas(struct mmu_gather **tlbp,
break;
}
tlb_finish_mmu(*tlbp, tlb_start, start);
if (need_resched() ||
(i_mmap_lock && spin_needbreak(i_mmap_lock))) {
if (i_mmap_lock) {
*tlbp = NULL;
if (i_mmap_lock)
goto out;
}
cond_resched();
}
*tlbp = tlb_gather_mmu(vma->vm_mm, fullmm);
tlb_start_valid = 0;
zap_work = ZAP_BLOCK_SIZE;
}
}
@ -1217,16 +1218,15 @@ unsigned long zap_page_range(struct vm_area_struct *vma, unsigned long address,
unsigned long size, struct zap_details *details)
{
struct mm_struct *mm = vma->vm_mm;
struct mmu_gather *tlb;
struct mmu_gather tlb;
unsigned long end = address + size;
unsigned long nr_accounted = 0;
lru_add_drain();
tlb = tlb_gather_mmu(mm, 0);
tlb_gather_mmu(&tlb, mm, 0);
update_hiwater_rss(mm);
end = unmap_vmas(&tlb, vma, address, end, &nr_accounted, details);
if (tlb)
tlb_finish_mmu(tlb, address, end);
tlb_finish_mmu(&tlb, address, end);
return end;
}

18
mm/mmap.c
View File

@ -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,