[PATCH 06/21] mm: update_hiwaters just in time
From: Hugh Dickins
Date: Wed Oct 12 2005 - 19:51:54 EST
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@xxxxxxxxxxx>
---
fs/compat.c | 1 -
fs/exec.c | 1 -
fs/proc/task_mmu.c | 23 +++++++++++++++++++++--
include/linux/mm.h | 3 ---
include/linux/sched.h | 10 ++++++++++
kernel/exit.c | 5 ++++-
kernel/sched.c | 2 --
mm/fremap.c | 4 +++-
mm/hugetlb.c | 3 +++
mm/memory.c | 17 +----------------
mm/mmap.c | 4 ++++
mm/mremap.c | 12 ++++++++++--
mm/nommu.c | 15 ++-------------
mm/rmap.c | 6 ++++++
14 files changed, 64 insertions(+), 42 deletions(-)
--- mm05/fs/compat.c 2005-09-21 12:16:40.000000000 +0100
+++ mm06/fs/compat.c 2005-10-11 23:54:32.000000000 +0100
@@ -1490,7 +1490,6 @@ int compat_do_execve(char * filename,
/* execve success */
security_bprm_free(bprm);
acct_update_integrals(current);
- update_mem_hiwater(current);
kfree(bprm);
return retval;
}
--- mm05/fs/exec.c 2005-09-30 11:59:08.000000000 +0100
+++ mm06/fs/exec.c 2005-10-11 23:54:33.000000000 +0100
@@ -1207,7 +1207,6 @@ int do_execve(char * filename,
/* execve success */
security_bprm_free(bprm);
acct_update_integrals(current);
- update_mem_hiwater(current);
kfree(bprm);
return retval;
}
--- mm05/fs/proc/task_mmu.c 2005-09-30 11:59:09.000000000 +0100
+++ mm06/fs/proc/task_mmu.c 2005-10-11 23:54:33.000000000 +0100
@@ -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);
--- mm05/include/linux/mm.h 2005-10-11 12:16:50.000000000 +0100
+++ mm06/include/linux/mm.h 2005-10-11 23:54:33.000000000 +0100
@@ -946,9 +946,6 @@ static inline void vm_stat_account(struc
}
#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)
--- mm05/include/linux/sched.h 2005-09-30 11:59:11.000000000 +0100
+++ mm06/include/linux/sched.h 2005-10-11 23:54:33.000000000 +0100
@@ -245,6 +245,16 @@ extern void arch_unmap_area_topdown(stru
#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 {
--- mm05/kernel/exit.c 2005-09-30 11:59:12.000000000 +0100
+++ mm06/kernel/exit.c 2005-10-11 23:54:33.000000000 +0100
@@ -839,7 +839,10 @@ fastcall NORET_TYPE void do_exit(long co
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);
--- mm05/kernel/sched.c 2005-09-30 11:59:12.000000000 +0100
+++ mm06/kernel/sched.c 2005-10-11 23:54:33.000000000 +0100
@@ -2603,8 +2603,6 @@ void account_system_time(struct task_str
cpustat->idle = cputime64_add(cpustat->idle, tmp);
/* Account for system time used */
acct_update_integrals(p);
- /* Update rss highwater mark */
- update_mem_hiwater(p);
}
/*
--- mm05/mm/fremap.c 2005-10-11 23:54:15.000000000 +0100
+++ mm06/mm/fremap.c 2005-10-11 23:54:33.000000000 +0100
@@ -140,8 +140,10 @@ int install_file_pte(struct mm_struct *m
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;
--- mm05/mm/hugetlb.c 2005-09-30 11:59:12.000000000 +0100
+++ mm06/mm/hugetlb.c 2005-10-11 23:54:33.000000000 +0100
@@ -309,6 +309,9 @@ void unmap_hugepage_range(struct vm_area
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)
--- mm05/mm/memory.c 2005-10-11 23:53:35.000000000 +0100
+++ mm06/mm/memory.c 2005-10-11 23:54:33.000000000 +0100
@@ -820,6 +820,7 @@ unsigned long zap_page_range(struct vm_a
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 @@ unsigned long vmalloc_to_pfn(void * vmal
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)
--- mm05/mm/mmap.c 2005-10-11 12:16:50.000000000 +0100
+++ mm06/mm/mmap.c 2005-10-11 23:54:33.000000000 +0100
@@ -1636,6 +1636,8 @@ find_extend_vma(struct mm_struct * mm, u
*/
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);
@@ -1664,6 +1666,7 @@ static void unmap_region(struct mm_struc
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,
@@ -1949,6 +1952,7 @@ void exit_mmap(struct mm_struct *mm)
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);
--- mm05/mm/mremap.c 2005-10-11 23:53:55.000000000 +0100
+++ mm06/mm/mremap.c 2005-10-11 23:54:33.000000000 +0100
@@ -167,6 +167,7 @@ static unsigned long move_vma(struct vm_
unsigned long new_pgoff;
unsigned long moved_len;
unsigned long excess = 0;
+ unsigned long hiwater_vm;
int split = 0;
/*
@@ -205,9 +206,15 @@ static unsigned long move_vma(struct vm_
}
/*
- * 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 @@ static unsigned long move_vma(struct vm_
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) {
--- mm05/mm/nommu.c 2005-09-30 11:59:12.000000000 +0100
+++ mm06/mm/nommu.c 2005-10-11 23:54:33.000000000 +0100
@@ -928,6 +928,8 @@ int do_munmap(struct mm_struct *mm, unsi
realalloc -= kobjsize(vml);
askedalloc -= sizeof(*vml);
kfree(vml);
+
+ update_hiwater_vm(mm);
mm->total_vm -= len >> PAGE_SHIFT;
#ifdef DEBUG
@@ -1075,19 +1077,6 @@ void arch_unmap_area(struct mm_struct *m
{
}
-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)
--- mm05/mm/rmap.c 2005-10-11 12:16:50.000000000 +0100
+++ mm06/mm/rmap.c 2005-10-11 23:54:33.000000000 +0100
@@ -538,6 +538,9 @@ static int try_to_unmap_one(struct page
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 @@ static void try_to_unmap_cluster(unsigne
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) {
-
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