Re: [PATCH, RESEND] introduce get_mm_hiwater_xxx(), fixtaskstats->hiwater_xxx accounting

[Hugh Dickins]

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@xxxxxxxxxx>

Acked-by: Hugh Dickins <hugh@xxxxxxxxxxx>

> 
> --- 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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