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Date: Fri, 12 Dec 2008 15:56:02 +0000 (GMT)
From: Hugh Dickins <hugh@...itas.com>
To: Oleg Nesterov <oleg@...hat.com>
cc: Andrew Morton <akpm@...ux-foundation.org>,
Balbir Singh <balbir@...ux.vnet.ibm.com>,
Jay Lan <jlan@....com>, Jiri Pirko <jpirko@...hat.com>,
Jonathan Lim <jlim@....com>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH, RESEND] introduce get_mm_hiwater_xxx(), fix
taskstats->hiwater_xxx accounting
On Fri, 12 Dec 2008, Oleg Nesterov wrote:
> (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@...hat.com>
Acked-by: Hugh Dickins <hugh@...itas.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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