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Subject[PATCH, RESEND] introduce get_mm_hiwater_xxx(), fix taskstats->hiwater_xxx accounting
(changes: update the changelog/comments)

xacct_add_tsk() relies on do_exit()->update_hiwater_xxx() and uses
mm->hiwater_xxx directly, this leads to 2 problems:

- taskstats_user_cmd() can call fill_pid()->xacct_add_tsk()
at any moment before the task exits, so we should check the
current values of rss/vm anyway.

- do_exit()->update_hiwater_xxx() calls are racy. An exiting
thread can be preempted right before mm->hiwater_xxx = new_val,
and another thread can use A_LOT of memory and exit in between.
When the first thread resumes it can be the last thread in the
thread group, in that case we report the wrong hiwater_xxx
values which do not take A_LOT into account.

Introduce get_mm_hiwater_rss() and get_mm_hiwater_vm() helpers and
change xacct_add_tsk() to use them. The first helper will also be
used by rusage->ru_maxrss accounting.

Kill do_exit()->update_hiwater_xxx() calls. Unless we are going to
decrease rss/vm there is no point to update mm->hiwater_xxx, and
nobody can look at this mm_struct when exit_mmap() actually unmaps
the memory.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>

--- K-28/include/linux/sched.h~HIWATER 2008-12-02 17:12:40.000000000 +0100
+++ K-28/include/linux/sched.h 2008-12-03 18:17:18.000000000 +0100
@@ -388,6 +388,9 @@ extern void arch_unmap_area_topdown(stru
(mm)->hiwater_vm = (mm)->total_vm; \
} while (0)

+#define get_mm_hiwater_rss(mm) max((mm)->hiwater_rss, get_mm_rss(mm))
+#define get_mm_hiwater_vm(mm) max((mm)->hiwater_vm, (mm)->total_vm)
+
extern void set_dumpable(struct mm_struct *mm, int value);
extern int get_dumpable(struct mm_struct *mm);

--- K-28/kernel/tsacct.c~HIWATER 2008-10-10 00:13:53.000000000 +0200
+++ K-28/kernel/tsacct.c 2008-12-03 18:24:28.000000000 +0100
@@ -90,8 +90,8 @@ void xacct_add_tsk(struct taskstats *sta
mm = get_task_mm(p);
if (mm) {
/* adjust to KB unit */
- stats->hiwater_rss = mm->hiwater_rss * PAGE_SIZE / KB;
- stats->hiwater_vm = mm->hiwater_vm * PAGE_SIZE / KB;
+ stats->hiwater_rss = get_mm_hiwater_rss(mm) * PAGE_SIZE / KB;
+ stats->hiwater_vm = get_mm_hiwater_vm(mm) * PAGE_SIZE / KB;
mmput(mm);
}
stats->read_char = p->ioac.rchar;
--- K-28/kernel/exit.c~HIWATER 2008-12-02 17:12:40.000000000 +0100
+++ K-28/kernel/exit.c 2008-12-03 18:21:06.000000000 +0100
@@ -1048,10 +1048,7 @@ NORET_TYPE void do_exit(long code)
preempt_count());

acct_update_integrals(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) {
hrtimer_cancel(&tsk->signal->real_timer);
--- K-28/mm/mmap.c~HIWATER 2008-12-02 17:12:40.000000000 +0100
+++ K-28/mm/mmap.c 2008-12-11 09:13:07.000000000 +0100
@@ -2103,7 +2103,7 @@ void exit_mmap(struct mm_struct *mm)
lru_add_drain();
flush_cache_mm(mm);
tlb = tlb_gather_mmu(mm, 1);
- /* Don't update_hiwater_rss(mm) here, do_exit already did */
+ /* 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);


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