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Subject[PATCH 2/8] mm: Remove i_mmap_mutex lockbreak
Hugh says:
"The only significant loser, I think, would be page reclaim (when
concurrent with truncation): could spin for a long time waiting for
the i_mmap_mutex it expects would soon be dropped? "

Counter points:
- cpu contention makes the spin stop (need_resched())
- zap pages should be freeing pages at a higher rate than reclaim
ever can
- shouldn't hold up reclaim more than lock_page() would

I think the simplification of the truncate code is definately worth
it.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
include/linux/fs.h | 1
include/linux/mm.h | 2
include/linux/mm_types.h | 1
kernel/fork.c | 1
mm/memory.c | 193 ++++++-----------------------------------------
mm/mmap.c | 13 ---
mm/mremap.c | 3
7 files changed, 27 insertions(+), 187 deletions(-)
Index: linux-2.6/include/linux/mm.h
===================================================================
--- linux-2.6.orig/include/linux/mm.h
+++ linux-2.6/include/linux/mm.h
@@ -878,8 +878,6 @@ struct zap_details {
struct address_space *check_mapping; /* Check page->mapping if set */
pgoff_t first_index; /* Lowest page->index to unmap */
pgoff_t last_index; /* Highest page->index to unmap */
- spinlock_t *i_mmap_lock; /* For unmap_mapping_range: */
- unsigned long truncate_count; /* Compare vm_truncate_count */
};

struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
Index: linux-2.6/mm/memory.c
===================================================================
--- linux-2.6.orig/mm/memory.c
+++ linux-2.6/mm/memory.c
@@ -986,13 +986,13 @@ int copy_page_range(struct mm_struct *ds
static unsigned long zap_pte_range(struct mmu_gather *tlb,
struct vm_area_struct *vma, pmd_t *pmd,
unsigned long addr, unsigned long end,
- long *zap_work, struct zap_details *details)
+ struct zap_details *details)
{
struct mm_struct *mm = tlb->mm;
int need_flush = 0;
- pte_t *pte;
- spinlock_t *ptl;
int rss[NR_MM_COUNTERS];
+ spinlock_t *ptl;
+ pte_t *pte;

init_rss_vec(rss);
again:
@@ -1001,12 +1001,9 @@ static unsigned long zap_pte_range(struc
do {
pte_t ptent = *pte;
if (pte_none(ptent)) {
- (*zap_work)--;
continue;
}

- (*zap_work) -= PAGE_SIZE;
-
if (pte_present(ptent)) {
struct page *page;

@@ -1073,8 +1070,7 @@ static unsigned long zap_pte_range(struc
print_bad_pte(vma, addr, ptent, NULL);
}
pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
- } while (pte++, addr += PAGE_SIZE,
- (addr != end && *zap_work > 0 && !need_flush));
+ } while (pte++, addr += PAGE_SIZE, (addr != end && !need_flush));

add_mm_rss_vec(mm, rss);
arch_leave_lazy_mmu_mode();
@@ -1093,7 +1089,7 @@ static unsigned long zap_pte_range(struc
static inline unsigned long zap_pmd_range(struct mmu_gather *tlb,
struct vm_area_struct *vma, pud_t *pud,
unsigned long addr, unsigned long end,
- long *zap_work, struct zap_details *details)
+ struct zap_details *details)
{
pmd_t *pmd;
unsigned long next;
@@ -1105,19 +1101,15 @@ static inline unsigned long zap_pmd_rang
if (next-addr != HPAGE_PMD_SIZE) {
VM_BUG_ON(!rwsem_is_locked(&tlb->mm->mmap_sem));
split_huge_page_pmd(vma->vm_mm, pmd);
- } else if (zap_huge_pmd(tlb, vma, pmd)) {
- (*zap_work)--;
+ } else if (zap_huge_pmd(tlb, vma, pmd))
continue;
- }
/* fall through */
}
- if (pmd_none_or_clear_bad(pmd)) {
- (*zap_work)--;
+ if (pmd_none_or_clear_bad(pmd))
continue;
- }
- next = zap_pte_range(tlb, vma, pmd, addr, next,
- zap_work, details);
- } while (pmd++, addr = next, (addr != end && *zap_work > 0));
+ next = zap_pte_range(tlb, vma, pmd, addr, next, details);
+ cond_resched();
+ } while (pmd++, addr = next, addr != end);

return addr;
}
@@ -1125,7 +1117,7 @@ static inline unsigned long zap_pmd_rang
static inline unsigned long zap_pud_range(struct mmu_gather *tlb,
struct vm_area_struct *vma, pgd_t *pgd,
unsigned long addr, unsigned long end,
- long *zap_work, struct zap_details *details)
+ struct zap_details *details)
{
pud_t *pud;
unsigned long next;
@@ -1133,13 +1125,10 @@ static inline unsigned long zap_pud_rang
pud = pud_offset(pgd, addr);
do {
next = pud_addr_end(addr, end);
- if (pud_none_or_clear_bad(pud)) {
- (*zap_work)--;
+ if (pud_none_or_clear_bad(pud))
continue;
- }
- next = zap_pmd_range(tlb, vma, pud, addr, next,
- zap_work, details);
- } while (pud++, addr = next, (addr != end && *zap_work > 0));
+ next = zap_pmd_range(tlb, vma, pud, addr, next, details);
+ } while (pud++, addr = next, addr != end);

return addr;
}
@@ -1147,7 +1136,7 @@ static inline unsigned long zap_pud_rang
static unsigned long unmap_page_range(struct mmu_gather *tlb,
struct vm_area_struct *vma,
unsigned long addr, unsigned long end,
- long *zap_work, struct zap_details *details)
+ struct zap_details *details)
{
pgd_t *pgd;
unsigned long next;
@@ -1161,13 +1150,10 @@ static unsigned long unmap_page_range(st
pgd = pgd_offset(vma->vm_mm, addr);
do {
next = pgd_addr_end(addr, end);
- if (pgd_none_or_clear_bad(pgd)) {
- (*zap_work)--;
+ if (pgd_none_or_clear_bad(pgd))
continue;
- }
- next = zap_pud_range(tlb, vma, pgd, addr, next,
- zap_work, details);
- } while (pgd++, addr = next, (addr != end && *zap_work > 0));
+ next = zap_pud_range(tlb, vma, pgd, addr, next, details);
+ } while (pgd++, addr = next, addr != end);
tlb_end_vma(tlb, vma);
mem_cgroup_uncharge_end();

@@ -1212,9 +1198,7 @@ unsigned long unmap_vmas(struct mmu_gath
unsigned long end_addr, unsigned long *nr_accounted,
struct zap_details *details)
{
- long zap_work = ZAP_BLOCK_SIZE;
unsigned long start = start_addr;
- spinlock_t *i_mmap_lock = details? details->i_mmap_lock: NULL;
struct mm_struct *mm = vma->vm_mm;

mmu_notifier_invalidate_range_start(mm, start_addr, end_addr);
@@ -1247,33 +1231,15 @@ unsigned long unmap_vmas(struct mmu_gath
* Since no pte has actually been setup, it is
* safe to do nothing in this case.
*/
- if (vma->vm_file) {
+ if (vma->vm_file)
unmap_hugepage_range(vma, start, end, NULL);
- zap_work -= (end - start) /
- pages_per_huge_page(hstate_vma(vma));
- }

start = end;
} else
- start = unmap_page_range(tlb, vma,
- start, end, &zap_work, details);
-
- if (zap_work > 0) {
- BUG_ON(start != end);
- break;
- }
-
- if (need_resched() ||
- (i_mmap_lock && spin_needbreak(i_mmap_lock))) {
- if (i_mmap_lock)
- goto out;
- cond_resched();
- }
-
- zap_work = ZAP_BLOCK_SIZE;
+ start = unmap_page_range(tlb, vma, start, end, details);
}
}
-out:
+
mmu_notifier_invalidate_range_end(mm, start_addr, end_addr);
return start; /* which is now the end (or restart) address */
}
@@ -2535,96 +2501,11 @@ static int do_wp_page(struct mm_struct *
return ret;
}

-/*
- * Helper functions for unmap_mapping_range().
- *
- * __ Notes on dropping i_mmap_lock to reduce latency while unmapping __
- *
- * We have to restart searching the prio_tree whenever we drop the lock,
- * since the iterator is only valid while the lock is held, and anyway
- * a later vma might be split and reinserted earlier while lock dropped.
- *
- * The list of nonlinear vmas could be handled more efficiently, using
- * a placeholder, but handle it in the same way until a need is shown.
- * It is important to search the prio_tree before nonlinear list: a vma
- * may become nonlinear and be shifted from prio_tree to nonlinear list
- * while the lock is dropped; but never shifted from list to prio_tree.
- *
- * In order to make forward progress despite restarting the search,
- * vm_truncate_count is used to mark a vma as now dealt with, so we can
- * quickly skip it next time around. Since the prio_tree search only
- * shows us those vmas affected by unmapping the range in question, we
- * can't efficiently keep all vmas in step with mapping->truncate_count:
- * so instead reset them all whenever it wraps back to 0 (then go to 1).
- * mapping->truncate_count and vma->vm_truncate_count are protected by
- * i_mmap_lock.
- *
- * In order to make forward progress despite repeatedly restarting some
- * large vma, note the restart_addr from unmap_vmas when it breaks out:
- * and restart from that address when we reach that vma again. It might
- * have been split or merged, shrunk or extended, but never shifted: so
- * restart_addr remains valid so long as it remains in the vma's range.
- * unmap_mapping_range forces truncate_count to leap over page-aligned
- * values so we can save vma's restart_addr in its truncate_count field.
- */
-#define is_restart_addr(truncate_count) (!((truncate_count) & ~PAGE_MASK))
-
-static void reset_vma_truncate_counts(struct address_space *mapping)
-{
- struct vm_area_struct *vma;
- struct prio_tree_iter iter;
-
- vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, 0, ULONG_MAX)
- vma->vm_truncate_count = 0;
- list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list)
- vma->vm_truncate_count = 0;
-}
-
-static int unmap_mapping_range_vma(struct vm_area_struct *vma,
+static void unmap_mapping_range_vma(struct vm_area_struct *vma,
unsigned long start_addr, unsigned long end_addr,
struct zap_details *details)
{
- unsigned long restart_addr;
- int need_break;
-
- /*
- * files that support invalidating or truncating portions of the
- * file from under mmaped areas must have their ->fault function
- * return a locked page (and set VM_FAULT_LOCKED in the return).
- * This provides synchronisation against concurrent unmapping here.
- */
-
-again:
- restart_addr = vma->vm_truncate_count;
- if (is_restart_addr(restart_addr) && start_addr < restart_addr) {
- start_addr = restart_addr;
- if (start_addr >= end_addr) {
- /* Top of vma has been split off since last time */
- vma->vm_truncate_count = details->truncate_count;
- return 0;
- }
- }
-
- restart_addr = zap_page_range(vma, start_addr,
- end_addr - start_addr, details);
- need_break = need_resched() || spin_needbreak(details->i_mmap_lock);
-
- if (restart_addr >= end_addr) {
- /* We have now completed this vma: mark it so */
- vma->vm_truncate_count = details->truncate_count;
- if (!need_break)
- return 0;
- } else {
- /* Note restart_addr in vma's truncate_count field */
- vma->vm_truncate_count = restart_addr;
- if (!need_break)
- goto again;
- }
-
- spin_unlock(details->i_mmap_lock);
- cond_resched();
- spin_lock(details->i_mmap_lock);
- return -EINTR;
+ zap_page_range(vma, start_addr, end_addr - start_addr, details);
}

static inline void unmap_mapping_range_tree(struct prio_tree_root *root,
@@ -2634,12 +2515,8 @@ static inline void unmap_mapping_range_t
struct prio_tree_iter iter;
pgoff_t vba, vea, zba, zea;

-restart:
vma_prio_tree_foreach(vma, &iter, root,
details->first_index, details->last_index) {
- /* Skip quickly over those we have already dealt with */
- if (vma->vm_truncate_count == details->truncate_count)
- continue;

vba = vma->vm_pgoff;
vea = vba + ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) - 1;
@@ -2651,11 +2528,10 @@ static inline void unmap_mapping_range_t
if (zea > vea)
zea = vea;

- if (unmap_mapping_range_vma(vma,
+ unmap_mapping_range_vma(vma,
((zba - vba) << PAGE_SHIFT) + vma->vm_start,
((zea - vba + 1) << PAGE_SHIFT) + vma->vm_start,
- details) < 0)
- goto restart;
+ details);
}
}

@@ -2670,15 +2546,9 @@ static inline void unmap_mapping_range_l
* across *all* the pages in each nonlinear VMA, not just the pages
* whose virtual address lies outside the file truncation point.
*/
-restart:
list_for_each_entry(vma, head, shared.vm_set.list) {
- /* Skip quickly over those we have already dealt with */
- if (vma->vm_truncate_count == details->truncate_count)
- continue;
details->nonlinear_vma = vma;
- if (unmap_mapping_range_vma(vma, vma->vm_start,
- vma->vm_end, details) < 0)
- goto restart;
+ unmap_mapping_range_vma(vma, vma->vm_start, vma->vm_end, details);
}
}

@@ -2717,19 +2587,8 @@ void unmap_mapping_range(struct address_
details.last_index = hba + hlen - 1;
if (details.last_index < details.first_index)
details.last_index = ULONG_MAX;
- details.i_mmap_lock = &mapping->i_mmap_lock;

spin_lock(&mapping->i_mmap_lock);
-
- /* Protect against endless unmapping loops */
- mapping->truncate_count++;
- if (unlikely(is_restart_addr(mapping->truncate_count))) {
- if (mapping->truncate_count == 0)
- reset_vma_truncate_counts(mapping);
- mapping->truncate_count++;
- }
- details.truncate_count = mapping->truncate_count;
-
if (unlikely(!prio_tree_empty(&mapping->i_mmap)))
unmap_mapping_range_tree(&mapping->i_mmap, &details);
if (unlikely(!list_empty(&mapping->i_mmap_nonlinear)))
Index: linux-2.6/include/linux/fs.h
===================================================================
--- linux-2.6.orig/include/linux/fs.h
+++ linux-2.6/include/linux/fs.h
@@ -640,7 +640,6 @@ struct address_space {
struct prio_tree_root i_mmap; /* tree of private and shared mappings */
struct list_head i_mmap_nonlinear;/*list VM_NONLINEAR mappings */
spinlock_t i_mmap_lock; /* protect tree, count, list */
- unsigned int truncate_count; /* Cover race condition with truncate */
unsigned long nrpages; /* number of total pages */
pgoff_t writeback_index;/* writeback starts here */
const struct address_space_operations *a_ops; /* methods */
Index: linux-2.6/include/linux/mm_types.h
===================================================================
--- linux-2.6.orig/include/linux/mm_types.h
+++ linux-2.6/include/linux/mm_types.h
@@ -175,7 +175,6 @@ struct vm_area_struct {
units, *not* PAGE_CACHE_SIZE */
struct file * vm_file; /* File we map to (can be NULL). */
void * vm_private_data; /* was vm_pte (shared mem) */
- unsigned long vm_truncate_count;/* truncate_count or restart_addr */

#ifndef CONFIG_MMU
struct vm_region *vm_region; /* NOMMU mapping region */
Index: linux-2.6/kernel/fork.c
===================================================================
--- linux-2.6.orig/kernel/fork.c
+++ linux-2.6/kernel/fork.c
@@ -379,7 +379,6 @@ static int dup_mmap(struct mm_struct *mm
spin_lock(&mapping->i_mmap_lock);
if (tmp->vm_flags & VM_SHARED)
mapping->i_mmap_writable++;
- tmp->vm_truncate_count = mpnt->vm_truncate_count;
flush_dcache_mmap_lock(mapping);
/* insert tmp into the share list, just after mpnt */
vma_prio_tree_add(tmp, mpnt);
Index: linux-2.6/mm/mmap.c
===================================================================
--- linux-2.6.orig/mm/mmap.c
+++ linux-2.6/mm/mmap.c
@@ -464,10 +464,8 @@ static void vma_link(struct mm_struct *m
if (vma->vm_file)
mapping = vma->vm_file->f_mapping;

- if (mapping) {
+ if (mapping)
spin_lock(&mapping->i_mmap_lock);
- vma->vm_truncate_count = mapping->truncate_count;
- }

__vma_link(mm, vma, prev, rb_link, rb_parent);
__vma_link_file(vma);
@@ -577,16 +575,7 @@ again: remove_next = 1 + (end > next->
if (!(vma->vm_flags & VM_NONLINEAR))
root = &mapping->i_mmap;
spin_lock(&mapping->i_mmap_lock);
- if (importer &&
- vma->vm_truncate_count != next->vm_truncate_count) {
- /*
- * unmap_mapping_range might be in progress:
- * ensure that the expanding vma is rescanned.
- */
- importer->vm_truncate_count = 0;
- }
if (insert) {
- insert->vm_truncate_count = vma->vm_truncate_count;
/*
* Put into prio_tree now, so instantiated pages
* are visible to arm/parisc __flush_dcache_page
Index: linux-2.6/mm/mremap.c
===================================================================
--- linux-2.6.orig/mm/mremap.c
+++ linux-2.6/mm/mremap.c
@@ -94,9 +94,6 @@ static void move_ptes(struct vm_area_str
*/
mapping = vma->vm_file->f_mapping;
spin_lock(&mapping->i_mmap_lock);
- if (new_vma->vm_truncate_count &&
- new_vma->vm_truncate_count != vma->vm_truncate_count)
- new_vma->vm_truncate_count = 0;
}

/*



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