[PATCH] mm: update_hiwaters just in time
update_mem_hiwater has attracted various criticisms, in particular from those
concerned with mm scalability. Originally it was called whenever rss or
total_vm got raised. Then many of those callsites were replaced by a timer
tick call from account_system_time. Now Frank van Maarseveen reports that to
be found inadequate. How about this? Works for Frank.
Replace update_mem_hiwater, a poor combination of two unrelated ops, by macros
update_hiwater_rss and update_hiwater_vm. Don't attempt to keep
mm->hiwater_rss up to date at timer tick, nor every time we raise rss (usually
by 1): those are hot paths. Do the opposite, update only when about to lower
rss (usually by many), or just before final accounting in do_exit. Handle
mm->hiwater_vm in the same way, though it's much less of an issue. Demand
that whoever collects these hiwater statistics do the work of taking the
maximum with rss or total_vm.
And there has been no collector of these hiwater statistics in the tree. The
new convention needs an example, so match Frank's usage by adding a VmPeak
line above VmSize to /proc/<pid>/status, and also a VmHWM line above VmRSS
(High-Water-Mark or High-Water-Memory).
There was a particular anomaly during mremap move, that hiwater_vm might be
captured too high. A fleeting such anomaly remains, but it's quickly
corrected now, whereas before it would stick.
What locking? None: if the app is racy then these statistics will be racy,
it's not worth any overhead to make them exact. But whenever it suits,
hiwater_vm is updated under exclusive mmap_sem, and hiwater_rss under
page_table_lock (for now) or with preemption disabled (later on): without
going to any trouble, minimize the time between reading current values and
updating, to minimize those occasions when a racing thread bumps a count up
and back down in between.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/fs/compat.c b/fs/compat.c
index a719e15..8e71cdb 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -1490,7 +1490,6 @@
/* execve success */
security_bprm_free(bprm);
acct_update_integrals(current);
- update_mem_hiwater(current);
kfree(bprm);
return retval;
}
diff --git a/fs/exec.c b/fs/exec.c
index cefadf5..9bb55c8 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1207,7 +1207,6 @@
/* execve success */
security_bprm_free(bprm);
acct_update_integrals(current);
- update_mem_hiwater(current);
kfree(bprm);
return retval;
}
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index bccee7c..7c89b45 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -14,22 +14,41 @@
char *task_mem(struct mm_struct *mm, char *buffer)
{
unsigned long data, text, lib;
+ unsigned long hiwater_vm, total_vm, hiwater_rss, total_rss;
+
+ /*
+ * Note: to minimize their overhead, mm maintains hiwater_vm and
+ * hiwater_rss only when about to *lower* total_vm or rss. Any
+ * collector of these hiwater stats must therefore get total_vm
+ * and rss too, which will usually be the higher. Barriers? not
+ * worth the effort, such snapshots can always be inconsistent.
+ */
+ hiwater_vm = total_vm = mm->total_vm;
+ if (hiwater_vm < mm->hiwater_vm)
+ hiwater_vm = mm->hiwater_vm;
+ hiwater_rss = total_rss = get_mm_rss(mm);
+ if (hiwater_rss < mm->hiwater_rss)
+ hiwater_rss = mm->hiwater_rss;
data = mm->total_vm - mm->shared_vm - mm->stack_vm;
text = (PAGE_ALIGN(mm->end_code) - (mm->start_code & PAGE_MASK)) >> 10;
lib = (mm->exec_vm << (PAGE_SHIFT-10)) - text;
buffer += sprintf(buffer,
+ "VmPeak:\t%8lu kB\n"
"VmSize:\t%8lu kB\n"
"VmLck:\t%8lu kB\n"
+ "VmHWM:\t%8lu kB\n"
"VmRSS:\t%8lu kB\n"
"VmData:\t%8lu kB\n"
"VmStk:\t%8lu kB\n"
"VmExe:\t%8lu kB\n"
"VmLib:\t%8lu kB\n"
"VmPTE:\t%8lu kB\n",
- (mm->total_vm - mm->reserved_vm) << (PAGE_SHIFT-10),
+ hiwater_vm << (PAGE_SHIFT-10),
+ (total_vm - mm->reserved_vm) << (PAGE_SHIFT-10),
mm->locked_vm << (PAGE_SHIFT-10),
- get_mm_rss(mm) << (PAGE_SHIFT-10),
+ hiwater_rss << (PAGE_SHIFT-10),
+ total_rss << (PAGE_SHIFT-10),
data << (PAGE_SHIFT-10),
mm->stack_vm << (PAGE_SHIFT-10), text, lib,
(PTRS_PER_PTE*sizeof(pte_t)*mm->nr_ptes) >> 10);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index da42093..7d4552f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -938,9 +938,6 @@
}
#endif /* CONFIG_PROC_FS */
-/* update per process rss and vm hiwater data */
-extern void update_mem_hiwater(struct task_struct *tsk);
-
#ifndef CONFIG_DEBUG_PAGEALLOC
static inline void
kernel_map_pages(struct page *page, int numpages, int enable)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index afcaac6..a9c0b7d 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -256,6 +256,16 @@
#define dec_mm_counter(mm, member) (mm)->_##member--
#define get_mm_rss(mm) ((mm)->_file_rss + (mm)->_anon_rss)
+#define update_hiwater_rss(mm) do { \
+ unsigned long _rss = get_mm_rss(mm); \
+ if ((mm)->hiwater_rss < _rss) \
+ (mm)->hiwater_rss = _rss; \
+} while (0)
+#define update_hiwater_vm(mm) do { \
+ if ((mm)->hiwater_vm < (mm)->total_vm) \
+ (mm)->hiwater_vm = (mm)->total_vm; \
+} while (0)
+
typedef unsigned long mm_counter_t;
struct mm_struct {
diff --git a/kernel/exit.c b/kernel/exit.c
index 3b25b18..79f52b8 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -839,7 +839,10 @@
preempt_count());
acct_update_integrals(tsk);
- update_mem_hiwater(tsk);
+ if (tsk->mm) {
+ update_hiwater_rss(tsk->mm);
+ update_hiwater_vm(tsk->mm);
+ }
group_dead = atomic_dec_and_test(&tsk->signal->live);
if (group_dead) {
del_timer_sync(&tsk->signal->real_timer);
diff --git a/kernel/sched.c b/kernel/sched.c
index 1e5cafd..4f26c54 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2511,8 +2511,6 @@
cpustat->idle = cputime64_add(cpustat->idle, tmp);
/* Account for system time used */
acct_update_integrals(p);
- /* Update rss highwater mark */
- update_mem_hiwater(p);
}
/*
diff --git a/mm/fremap.c b/mm/fremap.c
index 7f08d10..49719a3 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -143,8 +143,10 @@
if (!pte)
goto err_unlock;
- if (!pte_none(*pte) && zap_pte(mm, vma, addr, pte))
+ if (!pte_none(*pte) && zap_pte(mm, vma, addr, pte)) {
+ update_hiwater_rss(mm);
dec_mm_counter(mm, file_rss);
+ }
set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));
pte_val = *pte;
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 094455b..ac5f044 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -310,6 +310,9 @@
BUG_ON(start & ~HPAGE_MASK);
BUG_ON(end & ~HPAGE_MASK);
+ /* Update high watermark before we lower rss */
+ update_hiwater_rss(mm);
+
for (address = start; address < end; address += HPAGE_SIZE) {
ptep = huge_pte_offset(mm, address);
if (! ptep)
diff --git a/mm/memory.c b/mm/memory.c
index a25ee1d..692ad81 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -820,6 +820,7 @@
lru_add_drain();
spin_lock(&mm->page_table_lock);
tlb = tlb_gather_mmu(mm, 0);
+ update_hiwater_rss(mm);
end = unmap_vmas(&tlb, mm, vma, address, end, &nr_accounted, details);
tlb_finish_mmu(tlb, address, end);
spin_unlock(&mm->page_table_lock);
@@ -2225,22 +2226,6 @@
EXPORT_SYMBOL(vmalloc_to_pfn);
-/*
- * update_mem_hiwater
- * - update per process rss and vm high water data
- */
-void update_mem_hiwater(struct task_struct *tsk)
-{
- if (tsk->mm) {
- unsigned long rss = get_mm_rss(tsk->mm);
-
- if (tsk->mm->hiwater_rss < rss)
- tsk->mm->hiwater_rss = rss;
- if (tsk->mm->hiwater_vm < tsk->mm->total_vm)
- tsk->mm->hiwater_vm = tsk->mm->total_vm;
- }
-}
-
#if !defined(__HAVE_ARCH_GATE_AREA)
#if defined(AT_SYSINFO_EHDR)
diff --git a/mm/mmap.c b/mm/mmap.c
index 8a11179..c43b284 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1640,6 +1640,8 @@
*/
static void remove_vma_list(struct mm_struct *mm, struct vm_area_struct *vma)
{
+ /* Update high watermark before we lower total_vm */
+ update_hiwater_vm(mm);
do {
long nrpages = vma_pages(vma);
@@ -1668,6 +1670,7 @@
lru_add_drain();
spin_lock(&mm->page_table_lock);
tlb = tlb_gather_mmu(mm, 0);
+ update_hiwater_rss(mm);
unmap_vmas(&tlb, mm, vma, start, end, &nr_accounted, NULL);
vm_unacct_memory(nr_accounted);
free_pgtables(&tlb, vma, prev? prev->vm_end: FIRST_USER_ADDRESS,
@@ -1953,6 +1956,7 @@
flush_cache_mm(mm);
tlb = tlb_gather_mmu(mm, 1);
+ /* Don't update_hiwater_rss(mm) here, do_exit already did */
/* Use -1 here to ensure all VMAs in the mm are unmapped */
end = unmap_vmas(&tlb, mm, vma, 0, -1, &nr_accounted, NULL);
vm_unacct_memory(nr_accounted);
diff --git a/mm/mremap.c b/mm/mremap.c
index 318eea5..ccf4564 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -167,6 +167,7 @@
unsigned long new_pgoff;
unsigned long moved_len;
unsigned long excess = 0;
+ unsigned long hiwater_vm;
int split = 0;
/*
@@ -205,9 +206,15 @@
}
/*
- * if we failed to move page tables we still do total_vm increment
- * since do_munmap() will decrement it by old_len == new_len
+ * If we failed to move page tables we still do total_vm increment
+ * since do_munmap() will decrement it by old_len == new_len.
+ *
+ * Since total_vm is about to be raised artificially high for a
+ * moment, we need to restore high watermark afterwards: if stats
+ * are taken meanwhile, total_vm and hiwater_vm appear too high.
+ * If this were a serious issue, we'd add a flag to do_munmap().
*/
+ hiwater_vm = mm->hiwater_vm;
mm->total_vm += new_len >> PAGE_SHIFT;
vm_stat_account(mm, vma->vm_flags, vma->vm_file, new_len>>PAGE_SHIFT);
@@ -216,6 +223,7 @@
vm_unacct_memory(excess >> PAGE_SHIFT);
excess = 0;
}
+ mm->hiwater_vm = hiwater_vm;
/* Restore VM_ACCOUNT if one or two pieces of vma left */
if (excess) {
diff --git a/mm/nommu.c b/mm/nommu.c
index 59992488..dfb124f 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -931,6 +931,8 @@
realalloc -= kobjsize(vml);
askedalloc -= sizeof(*vml);
kfree(vml);
+
+ update_hiwater_vm(mm);
mm->total_vm -= len >> PAGE_SHIFT;
#ifdef DEBUG
@@ -1078,19 +1080,6 @@
{
}
-void update_mem_hiwater(struct task_struct *tsk)
-{
- unsigned long rss;
-
- if (likely(tsk->mm)) {
- rss = get_mm_rss(tsk->mm);
- if (tsk->mm->hiwater_rss < rss)
- tsk->mm->hiwater_rss = rss;
- if (tsk->mm->hiwater_vm < tsk->mm->total_vm)
- tsk->mm->hiwater_vm = tsk->mm->total_vm;
- }
-}
-
void unmap_mapping_range(struct address_space *mapping,
loff_t const holebegin, loff_t const holelen,
int even_cows)
diff --git a/mm/rmap.c b/mm/rmap.c
index f69d534..4c52c56 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -538,6 +538,9 @@
if (pte_dirty(pteval))
set_page_dirty(page);
+ /* Update high watermark before we lower rss */
+ update_hiwater_rss(mm);
+
if (PageAnon(page)) {
swp_entry_t entry = { .val = page->private };
/*
@@ -628,6 +631,9 @@
if (!pmd_present(*pmd))
goto out_unlock;
+ /* Update high watermark before we lower rss */
+ update_hiwater_rss(mm);
+
for (original_pte = pte = pte_offset_map(pmd, address);
address < end; pte++, address += PAGE_SIZE) {